Metal nanomaterials: Immune effects and implications of physicochemical properties on sensitization, elicitation, and exacerbation of allergic disease

Figures & data

Figure 1. Different morphologies of nanomaterials are shown: (a) graphene sheets, (b) silver nanoparticles, (c) silver nanowires, (d) gold nanorods, (e) gold nanoparticles, (f) nickel oxide nanoparticles, and (g) copper oxide nanoparticles.

Table 1. Metal nanomaterial production rates and corresponding applications.

Nanomaterial	Global production volume (tons)	Applications
Silicon dioxide	185,000–1,400,000	Nanocomposite filler, cement additive, drug delivery, cosmetics
Titanium dioxide	60,000–150,000	Ceramics, sunscreens, construction, energy, cosmetics
Zinc oxide	32,000–36,000	Sunscreen, LED and LCD displays, antimicrobial, water filtration
Aluminum oxide	5000–10,100	Drilling equipment, energetic fuels, and additives, filtration
Cerium oxide	880–1400	Catalysts, slurry polishing, UV absorption, anti-corrosion additive
Copper oxide	290–570	Heat transfer, batteries, antimicrobials, sensors, semiconduction
Silver	135–420	Biomedicine, antimicrobial textiles, cosmetics, conductive inks
Antimony tin oxide	120–225	Electronics, composites, coatings, research
Zirconium oxide	80–300	Heat-resistant coatings, ceramics, catalysts, dental composites
Iron oxide	9–45	Ground and wastewater cleanup, color imaging, drug delivery
Nickel	5–20	Ceramic additive, catalyst, energy absorption, electronics
Cobalt oxide	5–10	Electronics, catalysts, drug delivery, solar energy absorption
Quantum dots	4.5–9	Photovoltaic devices, photodetecting devices, electronics
Manganese oxide	2–3.5	Bleaching agent, biomedical diagnostics, plastics additive
Gold	1–3	Data storage, gene therapy, biosensors, fuel cell additive
Palladium	–	Hydrogen sensor, antimicrobial activity, catalysts

Metal nanomaterials, various applications, and reported global production volume for 2014, reported in tons. Adapted from Metal and Metal Oxide Nanomaterials Future Markets Report, Table 1 (Nanomaterials Future Markets 2015).

Figure 2. Steps of the Adverse Outcome Pathway (AOP) for dermal sensitization adapted from the Organization for Economic Cooperation and Development (OECD).

Figure 3. Potential adverse outcomes with respect to the sensitization and elicitation phases of allergy following exposure to immunotoxic agents. Adjuvant effects resulting from exposure prior to allergen sensitization can manifest as increased susceptibility to sensitization. Exposure concurrent to sensitization may lower the threshold of allergen exposure required to induce sensitization. Following sensitization to allergen, exposure to an immunotoxic agent either in the absence or presence of allergen may result in a lower threshold of exposure required to induce elicitation reactions or increased severity of elicitation symptoms. These effects may further increase susceptibility to elicitation reactions as result of physiological alterations such as compromised skin barrier integrity. Furthermore, isolated exposure to immunotoxic agents or concurrent to allergens in established allergic disease conditions may also contribute to the progression of chronic effects, such as airway remodeling, which can also further contribute to elicitation reactions.

Table 2. Summary of major findings from studies characterizing the effect of metal nanomaterials on dermal allergy grouped by metal.

Metal	Author/year	Material	Size	Animal or cell type	Model	Exposure route	Dose	Findings
Aluminum	Varlamova et al. 2015	Al2O3	–	M/F BALB/c, CBA/CaLac, outbred mice and guinea pig	LLNA	Subcutaneous, intramuscular, intravenous, intradermal injection	–	No intensification of anaphylaxis systemic reaction, no inflammatory reaction to ConA, no delayed allergic reaction, no redness or edema at site of application
	Brown et al. 2008	Al2O3	50–120 nm	HaCaT human keratinocytes	In vitro		10–10,000 µg/mL	24 h exposure resulted in IL-8 expression, IL-1α release, indicating potential for irritation or sensitization
Cobalt	Cho et al. 2012	Co3O4	18.4 ± 5.0 nm	F C57BL/6 mouse	OVA	Subcutaneous injection	25 µg	Balanced Th1/Th2 response when used as adjuvant, causing higher specific IgG2c and IgG1 and less IgE
Gold	Ishii et al. 2008	Au	5.2 ± 1.3 nm	F Japan White Rabbit	–	Intradermal injection	1 mg	Azobenzene dye hapten conjugation to AuNP led to high yield of IgG specific to the agent indicating the capacity for AuNP to act as both a carrier and adjuvant
Iron	Shen et al. 2012	Fe3O4	58.7 nm	M BALB/c mouse	OVA	Intravenously	0.2–10 mg/kg	Decreased footpad swelling, infiltration of macrophages and T-cells, and IFN-y, IL-6, TNF-α levels
	Hsiao et al. 2018	Fe3O4	58.7 nm	M BALB/c mouse	OVA	Intravenously	1–100 µg	Attenuation in TH17 responses
Silica	Choi et al. 2011	SiO2	7 nm	CBA/N mouse	HSEM LLNA	Dermal	10–1,000 µg	SiO2NP did not induce phototoxicity or skin sensitization
	Hirai et al. 2015	SiO2	30 nm	F NC/Nga slc mouse	HDM	Dermal	20 µL @ 12.5 mg/mL	Concurrent exposure to allergen and particles resulted in low-level production of allergen-specific IgG subtypes and increased sensitivity to anaphylaxis
	Ostrowski et al. 2014	SiO2	55 ± 6 nm	M SKH1 mouse	Oxazolone	Dermal	–	Functionalized nanoparticles had no impact on allergic response to oxazolone in an ACD model
	Smulders et al. 2015	SiO2	19 nm	M BALB/c mouse	DNCB	Dermal	0.4, 4.0, or 40 mg/mL×3 d	SiO2NP exposure prior to sensitization with DNCB did not alter the stimulation index
Silver	Kim et al. 2013	Ag	10 nm	M SPF guinea pig	GPMT	Intradermal injection	0.1 mL @ 1:1 (v/v)	No eye or skin irritation or corrosion. 1/20 guinea pigs developed erythema following subcutaneous injection, leading to its classification as a weak skin sensitizer
				M New Zealand White rabbit	–	Occular application	100 mg	No eye irritation effects 1–72 hours after exposure
	Bhol et al. 2005	Ag	<50 nm	F BALB/c mouse	DNFB	Dermal	100 mg 1% nanocrystalline	Reductions in ear swelling, erythema, and inflammation were seen after 4 days of treatment with nanoparticle-containing cream
	Smulders et al. 2015	Ag	25–85 nm	M BALB/c mouse	DNCB	Dermal	0.4, 4.0, or 40 mg/mL×3 d	Exposure prior to sensitization with DNCB did not alter the stimulation index
	Zelga et al. 2016	Ag	–	Guinea pig	GPMT	Dermal	2%	AgNP-containing dressings for chronic wounds were tested via GPMT, wherein 2/10 animals developed slight erythema that resolved after 72 hours, leading to classification as a mild sensitizer
	Korani et al. 2011	Ag	<100 nm	M Harley Albino guinea pig	–	Dermal	100–10,000 µg/ml	Dose-dependent increase in number of Langerhans cells recruited to skin
Titanium	Park et al. 2011	TiO2	<25 nm	F CBA/N mouse	LLNA	Dermal	10–1000 µg/mL	TiO2 did not induce skin sensitization
				F Hartley Albino guinea pig	–	Dermal	50 µg	TiO2 did not induce phototoxicity or acute cutaneous irritation
	Hussain et al. 2012	TiO2	12 ± 2 nm	M BALB/c mouse	DNCB	Subcutaneous Injection	0.004–0.4 mg/mL	TH2 adjuvancy, increased DNCB dermal sensitizer potency
	Auttachoat et al. 2014	TiO2	<25 nm	F BCC3F1 mouse	–	Dermal, Subcutaneous Injection	1.25–250 mg/kg	Dermal exposure did not induce auricular lymph node expansion, despite irritancy response at 5% and 10%, no ear swelling, but lymph node cell proliferation resulted following subcutaneous injection
	Smulders et al. 2015	TiO2	15 nm	M BALB/c mouse	DNCB	Dermal	0.4, 4.0, or 40 mg/mL×3 d	Exposure to 4.0 mg/mL of TiO2 prior to sensitization with DNCB resulted in increased stimulation index
	Piasecka-Zelga et al. 2015	TiO2	–	New Zealand albino rabbit	Acute Dermal Irritation	Dermal	0.5 g	5 UV-absorbers containing nano-sized particles were assessed for irritation and sensitization potential. Anatase TiO2–containing agent did not induce irritation, but caused mild sensitization
				Dunkin-Hartley guinea pig	GPMT	Dermal	0.1 mL/site
Zinc	Piasecka-Zelga et al. 2015	ZnO	APS 396 nm, containing nanoparticles	New Zealand albino rabbit	Acute Dermal Irritation	Dermal	0.5 g	5 UV-absorbers containing nano-sized particles were assessed for irritation and sensitization potential. Z11 modifier caused minor dermal irritation and mild sensitization
				Dunkin-Hartley guinea pig	GPMT	Dermal	0.1 mL/site
	Kim et al. 2016	ZnO	20–50 nm, 13.1 m^2/g	M Sprague-Dawley Rat, M New Zealand White rabbit, M guinea pig	GPMT	Dermal	50%	ZnONP did not induce dermal sensitization, acute dermal toxicity, irritation, or corrosion

Summary of studies investigating metal nanomaterial immune effects in the skin and select in vitro studies using dermal cells, grouped by metal. APS: average particle size, DNCB: dinitrochlorobenzene; GPMT: guinea pig maximization test; HDM: house dust mite; HSEM: Human Skin Equivalent Model; LLNA: Local Lymph Node Assay; OVA: ovalbumin; UV: ultraviolet.

Table 3. Summary of major findings from studies comparing the effects of various physicochemical properties of metal nanomaterials on dermal allergy grouped by property of interest.

Property investigated			Author/year	Metal	Study design	Property variations	Findings
Size			Kang H et al. 2017	Ag	RBL-2H3 mast cells F NC/Nga mouse, HDM AD: 40 µg	5, 100 nm AgNP	5 nm AgNP induced increases in ROS levels, intracellular calcium, and granule release in mast cells in vitro and earlier and more severe lesions in an AD model in vivo
			Nabeshi et al. 2010	Si	XS52 mouse epidermal Langerhans cell, 0.1–1000 µg/mL	70, 300, 1000 nm SiNP	Cellular uptake and cytotoxicity increased with reductions in particle size
			Yoshida et al. 2010	Si	XS52 mouse epidermal Langerhans cell, 0–100 µg/mL	70, 300, 1000 nm SiNP	ROS generation by LC was higher following exposure to the smaller amorphous SiNP
			Hirai et al. 2012b	Si	M NC/Nga mouse HDM ACD Intradermal injection: 250 µg	1136 nm SiO2NP: 33.2 mV, 264 nm SiO2NP: 25.8 mV, 106 nm SiO2NP: 24.3 mV, 76 nm SiO2NP: 19.5 mV, 39 nm SiO2NP: 14.0 mV	Reduction in size of SiO2NPs caused enhanced IL-18 and TSLP production, leading to an enhanced systemic Th2 response and aggravation of skin lesions following challenge with house dust mite
			Kang S et al. 2017b	Au	Mouse footpad injection OVA	7, 14, 28 nm AuNP	Size-dependent increase in cellular uptake by DC, T-cell cross-priming, and activation.after injection into footpad, higher delivery efficiency to lymph nodes was associated larger NPs
			Yanagisawa et al. 2009	Ti	M NC/Nga mouse HDM Intradermal injection: 20 µg	15 nm TiO2NP–110 m^2/g 50 nm TiO2NP–20–25 m^2/g 100 nm TiO2NP–10–15 m^2/g	TiO2NP aggravated AD skin lesions, caused increased IL-4 production, IgE levels, and histamine levels, but decreased IFN-γ expression. Effects were not dependent on size
			Ilves et al. 2014	Zn	F BALB/c mice, OVA ACD Dermal application: 16.67 mg/mL	20, 240 nm ZnONP	Smaller sized ZnONPs were able to penetrate the skin, whereas larger particles were not. Both particles diminished local skin inflammation, but ZnONPs exhibited higher suppressive effects and increased IgE production
	CRG		Jang et al. 2012	Zn	CBA/N Mouse LLNA: 25, 50, or 100 µg/mL ZnONP HSEM EpiDerm skin irritation Draize skin irritation: 50 µg/mL	20 nm, 29 mV or 40 mV ZnONP 100 nm, 24 mV or 29 mV ZnONP	ZnO are not dermal sensitizers and do not induce skin irritation irrespective of size and zeta potential, but may induce phototoxicity
			Jatanaet al 2017b	Si	M/F hairless C57BL6 mouse DNFB ACD Dermal application	32.7 nm SiO2 nanosphere: 25.4 mV 66.5 nm SiO2 nanosphere: 45.7 mV 69.3 nm SiO2 nanosphere: 17.7 mV 184.9 SiO2 nanosphere: 33.5 mV 440.0 nm SiO2 nanosphere: 66.0 mV	Small negative and neutral-charged nanoparticles exhibited an immunosuppressive effect, whereas positively-charged particles did not. Positively-charged nanoparticles penetrated skin to a lesser extent. Studies also included 100nm TiO2NP, 20 nm AgNP, and 20 nm AuNP
			Schaeublin et al. 2010	Au	HaCaT human keratinocyte cells 10 µg/mL–25 µg/mL	1.5 nm AuNP Positive, neutral, or negatively-charged	Cell morphology was disrupted by AuNPs of all 3 charges in a dose-dependent manner. Charged AuNPs caused dose-dependent cytotoxicity and mitochondrial stress
	CRY	SA	Lee et al. 2011	Si	J774A.1 mouse macrophages: 0–1,000 µg/mL, 1 or 3 d LLNA: F BALB/c, 1 mg/ear x 3 tx	100 nm spherical: mesoporous SiO2 1150 m^2/g colloidal SiO2–40 m^2/g	Higher surface area caused decreased cytotoxic and poptotic cell death. Similarly, higher surface area induced lower expression of pro-inflammatory cytokines. Lower surface area Si particles acted as an immunogenic sensitizer in the LLNA
Size			Maquieira et al. 2012	Al	Mice and rabbits Intradermal injection	40, 3000 nm amorphous Al2O3, 300 nm crystalline Al2O3	AlNP served as both carrier and adjuvant leading to hapten-specific antibody production dependent on size and crystallinity
			Braydich-Stolle et al. 2009	Ti	HEL-30 mouse keratinocytes 0–150 µg/mL 24 h exposure	100% anatase TiO2: 6.3, 10, 40, 50, 100 nm 61% anatase, 39% rutile TiO2: 39 nm 40% anatase, 60% rutile TiO2: 39 nm 75% anatase, 25% rutile TiO2: 26 nm Amorphous TiO2: 40 nm 100% rutile TiO2: 51 nm	Both size and crystal structure contributed to toxicity in vitro. Smaller size and less agglomeration increased cytotoxicity. 100% anatase TiO2 particles, regardless of size, induced cell necrosis, whereas the rutile TiO2 nanoparticles initiated apoptosis through formation of ROS
		MOD	Orlowski et al. 2013	Ag	291.03C mouse keratinocyte 1–10 µg/mL 24 h exposure	Tannic acid-modified AgNP: 13, 33, and 46 nm Unmodified AgNP: 10 -65 nm	Unmodified, but not modified, AgNP increased production of MCP-1 by keratinocytes and upregulation of TNF-α, attributable to increased ROS production
			Li et al. 2016	Si	F C57BL/6 mouse 5 mg injection	Unmodified mesoporous SiNP PEG, PEG-RGD, PEG-RDG- modified SiNP	PEG modification significantly enhanced DC activation in vitro and innate immune cell infiltration in vivo. PEG-modification resulted in less recruitment of DC to area of injection

Summary of study design and major findings from studies comparing the effects of various physicochemical properties of metal nanomaterials on dermal allergy grouped by study property of interest. Properties of interest: size, CRY (crystallinity), CRG (surface charge), SA (surface area), and MOD (surface modification). Reported particle size (nm), specific surface area (m²/g), zeta potential (mV), pore volume (cm³/g), in vitro dose concentration (µg/mL). DC: dendritic cell; DNFB: dinitrofluorobenzene; HDM: house dust mite; LC: Langerhans cell; LLNA: Local Lymph Node Assay; HSEM: Human Skin Equivalent Model; OVA: ovalbumin; PEG: poly(ethylene glycol) modification, PEG-RDG/RGD; ROS: reactive oxygen species; TSLP: thymic stromal lymphopoietin.

Table 4. Metal nanomaterials and corresponding physicochemical properties shown to influence immunological processes involved in the development and augmentation of ACD.

AOP Step	Metal nanomaterial effect	Metal	Properties implicated	Source
Sensitization
Bioavailability	Increased potential for nanomaterial penetration of intact skin	Au	size, crg	Labouta et al. 2011
	Increased potential for nanomaterial penetration of damaged skin	Ti	size, cry	Monteiro-Riviere et al. 2011
	Increased release of ions from parent nanomaterials	Pd	size	Filon et al. 2016
	Accumulation of nanomaterial in follicles and skin folds	Zn	mod	Leite-Silva et al. 2013
Molecular initating event	Increased potential for metal antigen formation	Ti	size	Vamanu et al. 2008
	Adsorbed protein conformational changes	Au	size	Bastus et al. 2009
Cellular response	Selective uptake by LC	Si	size	Nabeshi et al. 2010
	Direct activation of DC	Ti	size, cry, mor	Schanen et al. 2009
	Release of DAMPs from skin epithelial cells > activation of DC	Fe	size	Murray et al. 2013
	Release of DAMPs from dermal immune cells > activation of DC	Si	size, SA	Lee et al. 2011
	Altered immunogenicity from adsorption of LPS to surface	Au	size, mod, hyd	Li et al. 2017
Organ response	Depot formation > altered delivery kinetics	Si	agg	Hirai et al. 2015
	Nanomaterial antigen vehicle > altered delivery kinetics	Ti	–	Smulders et al. 2015
	Accumulation in DC endocytic compartments >  interference with antigen processing	Si	mod, crg	Shahbazi et al. 2014
	Enhanced capacity for cross-presentation to CD8+ T-cells	Fe	crg	Mou et al. 2017
	Increased TH1 signaling	Co	–	Cho et al. 2012
Elicitation
Organism response	Increased permeability of endothelial cells	Al	–	Oesterling et al. 2008
	Increased effector T-cell recruitment	many	–	Lozano-Fernandez et al. 2014
	Increased number of DC for T-cell activation	Si	mod	Li et al. 2016
	Increased number of skin macrophages	Fe	–	Yun et al. 2015
	Increased neutrophil influx to the skin	Ti	–	Goncalves, 2011
	Increased number of skin mast cells	Ag	size	Kang H et al. 2017
	Altered T-cell response to mitogens/allergens	Pd	size, sol	Reale et al. 2011
	Increased IgE-independent mast cell degranulation	many	size, SA, crg	Johnson et al. 2017
Chronic effects	Compromised skin repair mechanisms	Ag	–	Vieira et al. 2017
	Aggravation of allergic lesion severity	Si	size	Hirai et al. 2012b
	Compromised barrier integrity > increased penetration of allergens	Ag	size, sol	Koohi et al. 2011

Adverse Outcome Pathway (AOP) steps in the sensitization and elicitation phases of allergic contact dermatitis, metal nanomaterials shown to impact individual steps and cells involved, and physicochemical properties associated with effects are shown. Physicochemical properties of interest include size, agglomeration (agg), surface modification (mod), surface area (SA), solubility (sol), surface charge (crg), morphology (mor), crystallinity (cry), hydrophobicity (hyd), surface chemistry (SC). ND (not determined) notation in metal column indicates a study demonstrating a critical role for a specific nanomaterial physicochemical property on the cellular event, but was demonstrated using nonmetal nanomaterials. Findings may be applicable to metals, but have not been demonstrated with individual metal nanomaterials.

Table 5. Summary of major findings from studies characterizing the effect of metal nanomaterials on respiratory allergy grouped by metal.

Metal	Author/year	Material	Size	Animal or cell type	Model	Exposure route	Dose	Findings
Aluminum	Braydich-Stolle et al. 2010	Al	48.08 ± 21.0 nm	Human A549 type II pneumocyte U937 alveolar macrophage 3:1 co-culture	In vitro		5–500 µg/mL 24 h	Exposure impaired bacterial phagocytic function
		Al2O3	32.71 ± 28.3 nm					Exposure impaired bacterial phagocytic function, induction of NFκB pathway
Cerium	Park E-J et al. 2009	CeO2	130 nm	M ICR mouse	–	Intratracheal Instillation	50, 100, 200, 400 mg/kg	Differentiation of naïve T-cells and TH1 cytokine production
	Meldrum et al. 2018	CeO2	<25 nm APS 166.5 nm agglomerates	F BALB/c mouse	HDM	Intranasal Instillation	75 or 750 µg/kg	Repeated exposure to CeO2NP in the presence of HDM caused increased lung eosinophils, mast cells, plasma IgE, IL-4, and goblet cell metaplasia
Cobalt	Cho et al. 2012	Co3O4	18.4 ± 5.0 nm	F Wistar rat	–	Intratracheal Instillation	150 cm^2 SA	Exposure caused pulmonary alveolar proteinosis and TH1/TH17 dominant response
	Verstaelen et al. 2014	CoO	7.1 nm	BEAS-2B, A549 epithelial cells	In vitro		1–60 µg/mL	Alterations in expression of genes associated with innate immunity, T-cell activation, and leukocyte adhesion
Copper	Cho et al. 2012	CuO	23.1 ± 7.2 nm	F Wistar rat	–	Intratracheal Instillation	150 cm^2 SA	No immunoinflammatory reaction
	Park et al. 2015	CuO	<50 nm	F BALB/c mouse	OVA	Intranasal Instillation	25, 50, 100 µg/kg	Increased AHR, IgE and mucus production
	Lai et al. 2018	CuO	46.5 nm	C57BL/6 mouse	–	Intranasal delivery	1, 2.5, 5, 10 mg/kg	Aggravated pulmonary inflammation, collagen accumulation and expression of progressive fibrosis markers in lungs
Iron	Park et al. 2015	Fe2O3	101.3 ± 4.2 nm	M ICR mouse	–	Intratracheal instillation	0.5, 1, or 2 mg/kg	TH1-polarized inflammatory response, GM-CSF, MCP-1, and MIP-1 increase, and increased expression of CD80, CD86, and MHC II expression on lung APCs
	Park et al 2010c	Fe3O4	5.3 ± 3.6 nm	M ICR mouse	–	Intratracheal instillation	250, 500, 1,000 µg/kg	Increases in TH1/TH2 cytokines, B cells, and IgE levels
Gold	Hussain et al. 2011	Au	40 nm	M BALB/c mouse	TDI	Aspiration	40 µL @ 0.8 mg/kg	3x AHR increase
	Baretto et al. 2015	Au	6.3 nm	Swiss Webster and A/J mouse	OVA	Intranasal Instillation	6, 60 µg/kg	Inhibited allergen-induced accumulation of inflammatory cells, pro-inflammatory cytokine production. In A/J mice, AuNPs prevented mucus production and AHR
Nickel	Cho et al. 2012	NiO	5.3 nm	F Wistar rat	–	Intratracheal Instillation	150 cm^2 SA	Exposure caused pulmonary alveolar proteinosis and TH1/TH17 dominant responses
	Baker et al. 2016	Ni	20 nm	M C57BL/6 WT or T-bet-/- mouse	–	Aspiration	4 mg/kg	Increased airway remodeling in T-bet knockout mice with susceptibility to TH2 responses
	Lee et al. 2016	NiO	5.3 ± 0.4 nm	F Wistar rat	–	Intratracheal Instillation	50, 100, 200 cm^2	Acute neutrophilic inflammation, and eosinophils recruited at days 3 and 4 via eotaxin release
	Chang et al. 2017	NiO	–	M Wistar rat	–	Intratracheal Instillation	0.015–0.24 mg/kg	Alterations in TH1/TH2 balance were indicative of nitrative stress and NFk-B activation
Platinum	Park et al. 2010b	Pt	20.9 ± 11.4 nm	M ICR mouse	–	Intratracheal Instillation	–	Increase in serum IgE, lung TH2 cytokines, and decrease in CD4/8 ratio
	Onizawa et al. 2009	Pt	2 ± 0.4 nm	DBA/2 mouse	–	Intranasal instillation	x3 d	PtNP exerted protective effects from cigarette smoke, prevented NFk-B activation, and neutrophilic inflammation
Silica	Brandenberger et al. 2013	Si	90 nm	F BALB/c mouse	OVA	Intranasal instillation	0, 10, 100, 400 µg	Co-exposure during sensitization caused dose-dependent enhancement of OVA-specific IgE, lung eosinophils, mucus cell metaplasia, and TH2/TH17 cytokine production
Silver	Park H et al. 2010	Ag	6 ± 0.29 nm	F C57BL/6 mouse	OVA	Inhalation	5 x 20 ppm, 40 mg/kg	Decreased AHR, TH2 cytokines, and ROS levels
	Jang et al. 2012	Ag	6.0 ± 0.29 nm	F BALB/c mouse	OVA	Inhalation	20 ppm/40 mg/kg 5x for 24 h	Suppressed mucus production via VEGF signaling alterations
	Su et al. 2013	Ag	33 nm	F BALB/c mouse	OVA	Inhalation	3.3 ± 0.7 mg/m^3 6h/7 x 7 d	Increased OVA IgE, proteins associated with immune processes were altered
	Chuang et al. 2013	Ag	33 nm	F BALB/c mouse	OVA	Inhalation	3.3 mg/m^3 6h/d x 7 d	Increased Penh, recruitment of neutrophils, lymphocytes, and eosinophils to the airways
	Xu et al. 2013	Ag	141 nm	F BALB/c mouse	OVA	IP Injection	0.4, 2, 10 mg/kg	Increased OVA-IgG and TH2 responses, local activation and recruitment of leukocytes
Titanium	Ahn et al. 2005	TiO2	0.29 µm	M Sprague-Dawley rat	–	Intratracheal Instillation	4 mg/kg	Increased BAL IL-13 levels, IL-13-producing mast cells, and goblet cell hyperplasia
	Park et al. 2009	TiO2	20 nm	ICR mouse	–	Intratracheal Instillation	5, 20, or 50 mg/kg	Increased BAL and serum IgE levels, altered TH1/TH2 cytokines, increased B cell distribution
	Larsen et al. 2009	TiO2	28 nm	F BALB/c mouse	OVA	IP Injection	2–250 µg	TH2 adjuvancy, increased IgE, IgG1, and eosinophil levels
	Rossi et al. 2010	TiO2	10 x 40 nm	F BALC/c/Sca mouse	OVA	Inhalation	2 h/d, 3 d/w, x4 w @ 10 mg/m^3	Allergic pulmonary inflammation suppressed by TiO2NP
	Gustafsson et al. 2011	TiO2	21 nm	M Dark Agouti rat	–	Intratracheal instillation	5 mg/kg	Increased eosinophil, DC numbers in lungs, lymphocytes recruited mostly CD4+, also included CD8+ T-cells, B-cells, and CD25+ T-cells
	Hussain et al. 2011	TiO2	15 nm	M BALB/c mouse	TDI	Aspiration	40 µL @ 0.8 mg/kg	2x increase AHR
	Scarino et al. 2012	TiO2	5 nm APS, 168/171 nm agg.	M Brown Norway rat	OVA	Inhalation	9.4 or 15.7 mg/m^3	Significantly decreased lung leukocytes and plasma/BAL IL-4, IL-6, and IFN-γ over OVA controls
	Jonasson et al. 2013	TiO2	21 nm	F BALB/c mouse	OVA	Inhalation	32 ± 1 µg	Aggravated allergic response dependent on dose and timing
	Fu et al. 2014	TiO2	21 nm	M Sprague-Dawley rat	–	Intratracheal Instillation	0.5, 4.0, 32 mg/kg 2x/w x 4 w	Deposition in lymph nodes, increased T and B-cell proliferation following mitogen stimulation, enhanced NK activity in spleen, increased B-cells in the blood
	Choi et al. 2014	TiO2	P25	M New Zealand White Rabbit	–	Intratracheal instillation	10, 50, 250 µg	Dose-dependent eosinophil influx and inflammation in the lung, but not neutrophil or lymphocyte influx
	Gustafsson et al. 2014	TiO2	21 nm	M Dark Agouti rat M Brown Norway rat	OVA	Inhalation	168–159 µg/d x 10 d	Exposure decreased eosinophilia in OVA-sensitized DA and BN rats, but neutrophils/lymphocyte increase in DA rats
	Mishra et al. 2016	TiO2	4–8 nm	BALB/c mouse	OVA	IP Injection	200 µg	Augmented AHR, biochemical markers of damage, and induced a mixed TH1/TH2 response
	Kim et al. 2017	TiO2	75 nm	F BALB/c mouse	OVA	Inhalation	50 µg/m^3X 3 d	Exposure exacerbated AHR and inflammation, increases in IL-1, IL-18
Zinc	Roy et al 2014b	ZnO	<50 nm	F BALB/c mouse	OVA	IP Injection	0.25, 0.5, 1, 3 mg	Administration with OVA caused increased OVA-IgG1, IgE, eosinophil, and mast cell numbers in lungs and spleen
	Roy et al 2014a	ZnO	<50 nm	F BALB/c mouse	OVA	IP Injection	1, 2, 4, and 12 mg/mL	Adjuvant effect on OVA allergy by signaling through TLRs and Src kinase leading to inflammatory responses
	Huang et al. 2015	ZnO	181.5 nm low dose 360.0 nm high dose	F BALB/c mouse	OVA	Aspiration	0.1/0.5 mg/kg	Exposure simultaneous to OVA sensitization resulted in eosinophil recruitment and TH2 adjuvancy

Summary of findings from in vivo studies investigating immune effects of metal nanomaterials in the lung and select in vitro studies in pulmonary cells, grouped by metal. AHR: airway hyperreactivity; APC: antigen-presenting cell; APS: average particle size; DC: dendritic cell; HDM: house dust mite; IP: intraperitoneal; LPS: lipopolysaccharide; MHC: major histocompatibility complex; OVA: ovalbumin; ROS: reactive oxygen species; RSV: respiratory syncytial virus; TLR: Toll-like receptor; WT: wild-type.

Table 6. Summary of major findings from studies comparing the effects of various physicochemical properties of metal nanomaterials on respiratory allergy grouped by property of interest.

Property investigated			Author/year	Metal	Study design	Property variations	Findings
Size			de Haar et al. 2006	Ti	F BALB/cANNCrl mouse Ovalbumin, 200 µg intranasal	Fine TiO2: 250 nm, 6.6 m^2/g Ultrafine TiO2: 29.0 nm, 49.8 m^2/g	Exposure to equal mass doses of fine and ultrafine TiO2 resulted in increased TH2 cytokines and serum OVA-specific IgE and IgG1 only in animals exposed to ultrafine TiO2
			Yoshida et al. 2011	Si	F BALB/c mouse, Ovalbumin Intranasal: 10, 50, or 250 µg/ mouse x3	Amorphous silica 30, 70, 300, or 1000 nm	Smaller particles induced higher levels of OVA-specific IgE, IgG, and IgG1. Splenocytes from mice exposed to the smallest particle produced higher levels of TH2 cytokines than other groups.
			Liu et al. 2010	Ti	Rats, Intratracheal instillation 0.5, 5, or 50 µg/mL	5 or 200 nm TiO2	Decreased chemotactic ability, expression of Fc receptors/MHC II by alveolar macrophages. Phagocytic function was increased at low doses and decreased at high doses
			Chang et al. 2014	Ti	M Sprague Dawley rat Intratracheal instillation: x2, x4 w 0.5, 4, 32 mg/kg	21 nm TiO2NP: 80% anatase, 20% rutile, 1–2 µm TiO2: anatase	Increased macrophage accumulation and alteration of TH1/TH2 status
			Ban et al. 2013	Fe	F BALB/c mouse, Ovalbumin Intratracheal instillation: 4x (100, 250, or 500 µg/mouse)	Submicron Fe2O3: 147 ± 48 nm, 6 m^2/g Fe2O3NP: 35 ± 14 nm, 39 m^2/g	High and medium doses of both Fe particles caused decreases in eosinophil influx and OVA-specific IgE levels. However, at the low dose, submicron particles had no effect on allergy, whereas nanoparticles had an adjuvant effect on the TH2 response to OVA
	SA		Rossi et al. 2010	Ti	F BALB/c/Sca mouse, Ovalbumin Inhalation: 10 ± 2 mg/m^3 x 12	Rutile TiO2NP: <5 µm, 2 m^2/g Rutile TiO2NP: 10 x 40 nm, 132 m^2/g	Allergic pulmonary inflammation was dramatically suppressed in asthmatic mice exposed to either size TiO2. Leukocyte number, cytokines, chemokines, and antibodies were significantly decreased.
			Park et al. 2015	Si	F BALB/c mouse, Ovalbumin Intranasal inoculation	Spherical SiNP: 12.7 m^2/g Mesoporous SiNP: 70.6 m^2/g PEGylated SiNP: 12.7 m^2/g	Acute SiNP exposure induced significant airway inflammation and AHR. Spherical SiNPs induced the greatest degree of exacerbation of allergic effects in the OVA model
			Han et al. 2016	Si	F BALB/c mouse Ovalbumin Intranasal inoculation: 10 mg/kg 6x	Spherical SiNP: 12.7 m^2/g, 119.6 nm Mesoporous SiNP: 70.6 m^2/g, 100.5 nm PEGylated SiNP: 12.7 m^2/g, 439.1 nm	Sensitized mice exposed to S-SiNP and M-SiNP exhibited elevated AHR over controls. M-SiNPs induced the greatest degree adjuvanticity, whereas PEG-SiNP caused the least toxic effects
	MOD	CRG	Seydoux et al. 2016	Au	F BALB/c mouse AuNP intranasal instillation: 10 µg	90 nm AuNP: NH2-PVA, 7.2 mV COOH-PVA 8.2 mV	APCs preferentially took up cationic AuNPs, causing upregulation of co-stimulatory molecules. Positive AuNPs enhanced OVA-specific CD4+ T-cell stimulation in the lung draining lymph nodes
			Marzaioli et al. 2014	Si	F BALB/c mouse, Ovalbumin Intratracheal instillation: 50 µg	Amorphous SiO2NP 15 nm: Uncoated 38 mV, PEGylated 26 mV, Phosphate-coated 43 mV, Amino-coated 0 mV	Uncoated SiO2NPs induced proinflammatory and immunomodulatory effects with increases in lung inflammatory cells, TH2 cytokines. Amino and phosphate surface modifications mitigated these effects, whereas PEG coating did not.
			Omlor et al. 2017	Au	F BALB/c mouse, Ovalbumin Intranasal instillation	5 nm AuNP, PEGylated or citrated	Asthmatic condition increased nanoparticle uptake. Systemic uptake is higher for PEGylated AuNP compared to citrated AuNPs, but both inhibited inflammatory infiltrates and AHR, wherein inhibition was more significant following exposure to citrated AuNPS
			Vennemann et al. 2017	Zr	F Wistar rat Intratracheal instillation	APTS, TODS, PGA, or acrylic acid coated 9–10 nm ZrO2NPs	Surface coating had minimal effects on inflammation in the lungs of rats, but had significant effects on allergic response.
Size	MOD		Alessandrini et al. 2017	Ag	F BALB/c mice, Ovalbumin Intratracheal instillation: 1–50 µg	PVP-coated AgNP: 97 nm, 6.2 m^2/g, 7 mV PVP-coated AgNP: 134 nm, 4.5 m^2/g, 7 mV Citrate-AgNP: 20 nm, 30 m^2/g, 45 mV	Ag50-PVP significantly reduced OVA-induced inflammatory infiltrate in sensitized mice. Lung microbiome was altered dependent on coating.
			Seiffert et al. 2015	Ag	Brown Norway and Sprague-Dawley rats Intratracheal instillation: 0.1 mg/kg	PVP-coated AgNP: 20 or 110 nm Citrate-capped AgNP: 20 or 110 nm	Smaller AgNPs increased AHR on d 1, which persisted to d 7 for the citrate AgNPs only. 20 nm AgNP was more pro-inflammatory but little difference between different surface coatings
		CRY	Horie et al. 2015	Zn Ti Si	F C57BL/6N mouse, Ovalbumin Pharyngeal aspiration: 50 µg	Rutile TiO2, Al(OH)3 surf: 30-50 nm 37.1 m^2/g ZnO: 21 nm, 49.6 m^2/g ZnO, SiO2 Surface: 25 nm, unknown SA, ZnCl2 Amorphous SiO2: 7 nm 300 m^2/g, 34 nm 80 m^2/g	Serum total and OVA IgE, IgG1 increased in mice treated with the uncoated ZnO particle. However, ZnCl2 did not produce similar exacerbations. TiO2 and SiO2 did not affect OVA-IgE or IgG levels.
	SA		Sandberg et al. 2012	Si	LPS-primed RAW264.7 mouse macrophages, primary rat lung macrophages 0, 50, 100, 250, 500 µg/mL, 6 h	64 nm Si, 650 cm^2/mg 369 nm Si, 90 cm^2/mg ∼20 nm Fumed Si (aerosol), 1880 cm^2/mg 500 nm–10 µm Fused Si (suprasil), 23 cm^2/mg	Non-crystalline SiO2 particles in both nano and micron size ranges induced IL-1β release from LPS-primed macrophages following uptake, phagosomal leakage, and activation of the NALP3 inflammasome. Particle surface area, reactivity, and uptake all influenced the degree of mediator release by cells
			Vandebriel et al. 2018	Ti	F BALB/c mouse, Ovalbumin Intranasal exposure: 120 µg TiO2	Uncoated TiO2NP: 10–30 nm rutile or 10–25 nm anatase	Rutile TiO2NP caused the greatest increase in OVA-specific serum IgE and IgG1. Neutrophils recruited by rutile, but not anatase
		SOL	Jeong et al. 2015	Co	F Rat, Intratracheal Instillation 80, 200, 800 µg/mL @ 0.5 mL	CoO: 65.4 ± 2.8 nm, 92.65% solubility Co3O4: 20.2 ± 0.4 nm, 11.46% solubility	Soluble CoNP induced eosinophilic inflammation, whereas insoluble CoONP induced neutrophilic inflammation
			Cho et al. 2011	Zn	F Wistar rat Intratracheal instillation	10.7 ± 0.7 nm ZnONP 50 or 150 cm^2/rat Zn^2+ ions 92.5 µg/rat	ZnONP induced eosinophilia, proliferation of airway epithelial cells, goblet cell hyperplasia, and increased IgE levels, and decreased IgA- findings which were also seen following instillation of Zn ions

Summary of study design and major findings from studies comparing the effects of various physicochemical properties of metal nanomaterials on respiratory allergy grouped by study property of interest. Properties of interest: size, CRY (crystallinity), MOR (morphology), MOD (surface modification), CRG (surface charge), and SA (surface area), and SOL (solubility). Reported particle size (nm), specific surface area (m²/g), zeta potential (mV), pore volume (cm³/g), in vitro dose concentration (µg/mL). AHR: airway hyperreactivity; APC: antigen-presenting cell; APTS: aminopropylsilane modification; DC-SIGN: dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin; MDDC: monocyte-derived dendritic cell; MHC: major histocompatibility complex; OVA: ovalbumin; PDI: polydispersity index; PEG: poly(ethylene glycol) modification; PGA: poly(lactic-co-glycolic acid) modification; PVA: PVP polyvinylpyrrolidone modification; ROS: reactive oxygen species; TODS: tetraoxidecanoic acid modification

Table 7. Metal nanomaterials and corresponding physicochemical properties shown to influence immunological processes involved in the development and augmentation of asthma.

AOP step	Metal nanomaterial effect	Metal	Properties implicated	Source
Sensitization
Bioavailability	Increased potential for inhalation	many	dustiness	Evans et al. 2003
	Evasion of uptake by pulmonary macrophages	Si	size, crg, mod	Oh et al. 2010
	Evasion of entrapment by pulmonary mucus	ND	size, crg	Murgia et al. 2016
	Prolonged retention in airways	Al	spec, mor	Park et al. 2017
	Direct translocation across lung epithelial tissue to lymphatics	Au	size, crg	Kreyling et al. 2014
Molecular initating event	Increased potential for metal antigen formation	Ti	size	Vamanu et al. 2008
	Increased protease activity of protein allergens	Au	–	Radauer-Preiml et al. 2016
Cellular response	Adsorption of LPS to nanomaterial surface	Au	size, hyd, mod	Li et al. 2017
	Increased recruitment of DC to lung	Al	mod	Li et al. 2010
	Direct activation of DC	Ti	size, cry	Winter et al. 2011
	Release of DAMPs from immune cells > activation of DC	Zn	size, mor, SA	Hsaio et al. 2011
	Release of DAMPs from epithelial cells > activation of DC	Ag	size, mod, SA, sol	Hamilton et al. 2014
Organ response	Increased CD4^+ T-cell presentation efficiency	Ti	size, mor, cry	Schanen et al. 2009
	Increased polarization of CD4^+ T-cells to TH2 phenotype	Si	size, mod, SA	Vallhov et al. 2012
	Increased number of B-cells	Ti	–	Park et al. 2009
	Alteration in B-cell expansion/maturation	Au	size	Lee et al. 2014
	Increased production of total IgE	Pt	–	Park et al. 2010b
	Increased production of allergen-specific IgE	Zn	size, sol, cry	Horie et al. 2015
Elicitation
Organism response-early phase reaction	Increased IgE-dependent mast cell degranulation	Au	size, mod	Huang et al. 2009
	Increased IgE-independent mast cell degranulation	many	size, SA, crg	Johnson et al. 2017
	Increased number of lung mast cells	Ce	–	Meldrum et al. 2018
	Altered mast cell exocytic function and granule release	Si	SA	Maurer-Jones et al. 2010
	Altered expression of Fc receptors on immune cells	Ti	size	Liu et al. 2010
Organism response- late phase reaction	Increased endothelial adhesion molecule expression	Al	–	Oesterling et al. 2008
	Increased neutrophil recruitment	Ag	size, sol	Arai et al. 2015
	Increased eosinophil recruitment	Co	sol	Jeong et al. 2015
	Increased lymphocyte recruitment	Zr	mod	Vennemann et al. 2017
	Increased AHR	Ag	size, mod	Seiffert et al. 2015
	Increased airway smooth muscle contractility	Co/Fe	–	Kapilevich et al. 2012
	Mucus cell metaplasia/muus hyeprsecretion	Ti	–	Chen et al. 2011
Chronic effects	Epithelial cell proliferation	Zn	sol	Cho et al. 2011
	Increased fibroblast MMP activity extracellular matrix remodeling	Ti	size, cry, mor	Armand et al. 2012
	Myofibroblast accumulation	Cu	–	Lai et al. 2018

Adverse Outcome Pathway (AOP) steps involved in the sensitization and elicitation phases of asthma, metal nanomaterials shown to impact individual steps, and physicochemical properties associated with effects are shown. Physicochemical properties of interest include size, metal speciation (spec), agglomeration (agg), surface modification (mod), surface area (SA), solubility (sol), surface charge (crg), morphology (mor), crystallinity (cry), and hydrophobicity (hyd). ND (not determined) notation in metal column indicates a study demonstrating a critical role for a specific nanomaterial physicochemical property on the cellular event, but was demonstrated using nonmetal nanomaterials. Findings may be applicable to metals, but have not been demonstrated with individual metal nanomaterials.

Nanomaterials Future Markets. 2015. Metal & Metal Oxide: Forecast from 2010 to 2025. Future Markets, Inc.

 Google Scholar

Ishii N, Fitrilawati F, Manna A, Akiyama H, Tamada Y, Tamada K. 2008. Gold nanoparticles used as a carrier enhance production of anti-hapten IgG in rabbit: A study with azobenzene-dye as a hapten presented on the entire surface of gold nanoparticles. Biosci Biotechnol Biochem. 72:124–131.

 PubMed Web of Science ®Google Scholar

Shen C, Liang H, Wang C, Liao M, Jan T. 2012. Iron oxide nanoparticles suppressed T-helper-1 cell-mediated immunity in a murine model of delayed-type hypersensitivity. Int J Nanomed. 7:2729–2737.

 PubMed Web of Science ®Google Scholar

Hsiao Y, Shen C, Huang C, Lin Y, Jan T. 2018. Iron oxide nanoparticles attenuate T helper 17 cell responses in vitro and in vivo. Int Immunopharmacol. 58:32–39.

 PubMed Web of Science ®Google Scholar

Choi J, Park Y, Lee E, Jeong S, Kim S, Kim M, Son S. 2011. A safety assessment of phototoxicity and sensitization of SiO2 nanoparticles. Mol Cell Toxicol. 7:171–176.

 Web of Science ®Google Scholar

Hirai T, Yoshioka Y, Takahashi H, Ichihashi K, Udaka A, Mori T, Nishijima N, Yoshida T, Nagano K, Kamada H, et al. 2015. Cutaneous exposure to agglomerates of silica nanoparticles and allergen results in IgE-biased immune response and increased sensitivity to anaphylaxis in mice. Particle Fibre Toxicol. 12:16.

 PubMed Web of Science ®Google Scholar

Ostrowski A, Nordmeyer D, Mundhenk L, Fluhr J, Lademann J, Graf C, Rühl E, Gruber A. 2014. AHAPS-functionalized silica nanoparticles do not modulate allergic contact dermatitis in mice. Nanoscale Res Lett. 9:524.

 PubMed Web of Science ®Google Scholar

Smulders S, Golanski L, Smolders E, Vanoirbeek J, Hoet P. 2015. Nano-TiO2 modulates the dermal sensitization potency of dinitrochlorobenzene after topical exposure. Br J Dermatol. 172:392–399.

 PubMed Web of Science ®Google Scholar

Kim J, Song K, Sung J, Ryu H, Choi B, Cho H, Lee J, Yu I. 2013. Genotoxicity, acute oral and dermal toxicity, eye and dermal irritation and corrosion and skin sensitisation evaluation of silver nanoparticles. Nanotoxicology. 7:953–960.

 PubMed Web of Science ®Google Scholar

Zelga PJ, Górnicz MM, Głuszkiewicz JM, Piasecka-Zelga J. 2016. Outcomes of acute dermal irritation and sensitisation tests on active dressings for chronic wounds: A comparative study. J Wound Care. 25:722–729.

 PubMed Web of Science ®Google Scholar

Korani M, Rezayat S, Gilani K, Bidgoli S, Adeli S. 2011. Acute and subchronic dermal toxicity of nanosilver in guinea pig. Int J Nanomedicine. 6:855.

 PubMed Web of Science ®Google Scholar

Park Y, Jeong S, Yi S, Choi B, Kim Y, Kim I, Kim M, Son S. 2011. Analysis for the potential of polystyrene and TiO2 nanoparticles to induce skin irritation, phototoxicity, and sensitization. Toxicol In Vitro. 25:1863–1869.

 PubMed Web of Science ®Google Scholar

Hussain S, Smulders S, de Vooght V, Ectors B, Boland S, Marano F, van Landuyt KL, Nemery B, Hoet P, Vanoirbeek J. 2012. Nano-titanium dioxide modulates the dermal sensitization potency of DNCB. Particle Fibre Toxicol. 9:15.

 PubMed Web of Science ®Google Scholar

Auttachoat W, McLoughlin C, White K, Smith M. 2014. Route-dependent systemic and local immune effects following exposure to solutions prepared from titanium dioxide nano-particles. J Immunotoxicol. 11:273–282.

 PubMed Web of Science ®Google Scholar

Piasecka-Zelga J, Zelga P, Górnicz M, Strzelczyk P, Sójka-Ledakowicz J. 2015. Acute dermal toxicity and sensitization studies of novel nano-enhanced UV absorbers. J Occup Health. 57:275–284.

 PubMed Web of Science ®Google Scholar

Kim S, Heo Y, Choi S, Kim Y, Kim M, Kim H, Jo E, Song C, Lee K. 2016. Safety evaluation of zinc oxide nanoparticles in terms of acute dermal toxicity, dermal irritation and corrosion, and skin sensitization. Mol Cell Toxicol. 12:93–99.

 Web of Science ®Google Scholar

Kang H, Kim S, Lee K, Jin S, Kim S, Lee K, Jeon H, Song Y, Lee S, Seo J, et al. 2017. 5-nm Silver nanoparticles amplify clinical features of atopic dermatitis in mice by activating mast cells. Small. 13(9). DOI:10.1002/smll.201602363.

 Web of Science ®Google Scholar

Nabeshi H, Yoshikawa T, Matsuyama K, Nakazato Y, Arimori A, Isobe M, Tochigi S, Kondoh S, Hirai T, Akase T, et al. 2010. Size-dependent cytotoxic effects of amorphous silica nanoparticles on Langerhans cells. Pharmazie. 65:199–201.

 PubMed Web of Science ®Google Scholar

Hirai T, Yoshikawa T, Nabeshi H, Yoshida T, Tochigi S, Ichihashi K, Uji M, Akase T, Nagano K, Abe Y, et al. 2012b. Amorphous silica nanoparticles size-dependently aggravate atopic dermatitis-like skin lesions following an intradermal injection. Particle Fibre Toxicol. 9:3.

 PubMed Web of Science ®Google Scholar

Kang S, Ahn S, Lee J, Kim J, Choi M, Gujrati V, Kim H, Kim J, Shin E, Jon S. 2017. Effects of gold nanoparticle-based vaccine size on lymph node delivery and cytotoxic T-lymphocyte responses. J Control Rel. 256:56–67.

 PubMed Web of Science ®Google Scholar

Yanagisawa R, Takano H, Inoue K, Koike E, Kamachi T, Sadakane K, Ichinose T. 2009. Titanium dioxide nanoparticles aggravate atopic dermatitis-like skin lesions in nc/nga mice. Exp Biol Med. 234:314–322.

 Web of Science ®Google Scholar

Ilves M, Palomaki J, Vippola M, Lehto M, Savolainen K, Savinko T, Alenius H. 2014. Topically-applied ZnO nanoparticles suppress allergen induced skin inflammation but induce vigorous IgE production in the atopic dermatitis mouse model. Particle Fibre Toxicol. 11:38.

 PubMed Web of Science ®Google Scholar

Jang S, Park J, Cha H, Jung S, Lee J, Jung S, Kim J, Kim S, Lee C, Park H. 2012. Silver nanoparticles modify VEGF signaling pathway and mucus hypersecretion in allergic airway inflammation. Intl J Nanomed. 7:1329–1343.

 PubMed Web of Science ®Google Scholar

Jatana S, Palmer B, Phelan S, Gelein R, DeLouise L. 2017b. In vivo quantification of quantum dot systemic transport in C57BL/6 hairless mice following skin application post-ultraviolet radiation. Particle Fibre Toxicol. 14:12.

 PubMed Web of Science ®Google Scholar

Lee S, Yun H, Kim S. 2011. The comparative effects of mesoporous silica nanoparticles and colloidal silica on inflammation and apoptosis. Biomaterials. 32:9434–9443.

 PubMed Web of Science ®Google Scholar

Maquieira Á, Brun EM, Garcés-García M, Puchades R. 2012. Aluminum oxide nanoparticles as carriers and adjuvants for eliciting antibodies from non-immunogenic haptens. Anal Chem. 84:9340–9348.

 PubMed Web of Science ®Google Scholar

Braydich-Stolle L, Schaeublin N, Murdock R, Jiang J, Biswas P, Schlager J, Hussain S. 2009. Crystal structure mediates mode of cell death in TiO2 nanotoxicity. J Nanopart Res. 11:1361–1374.

 Web of Science ®Google Scholar

Labouta H, el-Khordagui L, Kraus T, Schneider M. 2011. Mechanism and determinants of nanoparticle penetration through human skin. Nanoscale. 3:4989–4999.

 PubMed Web of Science ®Google Scholar

Monteiro-Riviere N, Wiench K, Landsiedel R, Schulte S, Inman A, Riviere J. 2011. Safety evaluation of sunscreen formulations containing titanium dioxide and zinc oxide nanopar-ticles in UVB-sunburned skin: An in vitro and in vivo study. Toxicol Sci. 123:264–280.

 PubMed Web of Science ®Google Scholar

Filon F, Crosera M, Mauro M, Baracchini E, Bovenzi M, Montini T, Fornasiero P, Adami G. 2016. Palladium nanoparticles exposure: Evaluation of permeation through damaged and intact human skin. Environ Pollut. 214:497–503.

 PubMed Web of Science ®Google Scholar

Leite-Silva VR, Le Lamer M, Sanchez WY, Liu DC, Sanchez WH, Morrow I, Martin D, Silva HDT, Prow TW, Grice JE, et al. 2013. The effect of formulation on the penetration of coated and uncoated zinc oxide nanoparticles into the viable epidermis of human skin in vivo. Eur J Pharm Biopharm. 84:297–308.

 PubMed Web of Science ®Google Scholar

Vamanu C, Høl P, Allouni Z, Elsayed S, Gjerdet N. 2008. Formation of potential titanium antigens based on protein binding to titanium dioxide nanoparticles. Int J Nanomed. 3:69–74.

 PubMed Web of Science ®Google Scholar

Murray AR, Kisin E, Inman A, Young S-H, Muhammed M, Burks T, Uheida A, Tkach A, Waltz M, Castranova V, et al. 2013. Oxidative stress and dermal toxicity of iron oxide nanoparticles in vitro. Cell Biochem Biophys. 67:461–476.

 PubMed Web of Science ®Google Scholar

Li Y, Shi Z, Radauer-Preiml I, Andosch A, Casals E, Luetz-Meindl U, Cobaleda M, Lin Z, Jaberi-Douraki M, Italiani P, et al. 2017. Bacterial endotoxin (lipopolysaccharide) binds to the surface of gold nanoparticles, interferes with biocorona formation and induces human monocyte inflammatory activation. Nanotoxicology. 11:1157–1175.

 PubMed Web of Science ®Google Scholar

Shahbazi M, Almeida P, Makila E, Kaasalainen M, Salonen J, Hirvonen J, Santos H. 2014. Augmented cellular trafficking and endosomal escape of porous silicon nanoparticles via zwitterionic bilayer polymer surface engineering. Biomaterials. 35:7488–7500.

 PubMed Web of Science ®Google Scholar

Mou Y, Xing Y, Ren H, Cui Z, Zhang Y, Yu G, Urba WJ, Hu Q, Hu H. 2017. Effect of super-paramagnetic iron oxide nanoparticle surface charge on antigen cross-presentation. Nanoscale Res Lett. 12:52.

 PubMed Web of Science ®Google Scholar

Reale M, Vianale G, Lotti L, Mariani-Costantini R, Perconti S, Cristaudo A, Leopold K, Anto-nucci A, di Giampaolo L, Iavicoli I, et al. 2011. Effects of Palladium nanoparticles on the cytokine release from peripheral blood mononuclear cells of palladium-sensitized women. J Occup Environ Med. 53:1054–1060.

 PubMed Web of Science ®Google Scholar

Johnson M, Mendoza R, Raghavendra A, Podila R, Brown J. 2017. Contribution of engineered nanomaterials physicochemical properties to mast cell degranulation. Sci Rep. 7:43570.

 PubMed Web of Science ®Google Scholar

Braydich-Stolle L, Speshock J, Castle A, Smith M, Murdock R, Hussain S. 2010. Nanosized aluminum altered immune function. ACS Nano. 4:3661–3670.

 PubMed Web of Science ®Google Scholar

Park E, Yoon J, Choi K, Yi J, Park K. 2009. Induction of chronic inflammation in mice treated with titanium dioxide nanoparticles by intratracheal instillation. Toxicology. 260:37–46.

 PubMed Web of Science ®Google Scholar

Meldrum K, Robertson S, Römer I, Marczylo T, Dean L, Rogers A, Gant T, Smith R, Tetley T, Leonard M. 2018. Cerium dioxide nanoparticles exacerbate house dust mite-induced Type II airway inflammation. Particle Fibre Toxicol. 15:24.

 PubMed Web of Science ®Google Scholar

Park E, Kim H, Kim Y, Yi J, Choi K, Park K. 2010c. Inflammatory responses may be induced by a single intratracheal instillation of iron nanoparticles in mice. Toxicology. 275:65–71.

 PubMed Web of Science ®Google Scholar

Hussain S, Vanoirbeek J, Luyts K, de Vooght V, Verbeken E, Thomassen L, Martens J, Dinsdale D, Boland S, Marano F, et al. 2011. Lung exposure to nanoparticles modulates an asthmatic response in a mouse model. Eur Respir J. 37:299–309.

 PubMed Web of Science ®Google Scholar

Lee S, Hwang S, Jeong J, Han Y, Kim S, Lee D, Lee H, Chung S, Jeong J, Roh C. 2016. Nickel oxide nanoparticles can recruit eosinophils in the lungs of rats by the direct release of intracellular eotaxin. Particle Fibre Toxicol. 13.

 Web of Science ®Google Scholar

Park E, Kim H, Kim Y, Park K. 2010b. Intratracheal instillation of platinum nanoparticles may induce inflammatory responses in mice. Arch Pharm Res. 33:727–735.

 PubMed Web of Science ®Google Scholar

Brandenberger C, Rowley N, Jackson-Humbles D, Zhang Q, Bramble L, Lewandowski R, Wagner J, Chen W, Kaplan B, Kaminski N, et al. 2013. Engineered silica nanoparticles act as adjuvants to enhance allergic airway disease in mice. Part Fibre Toxicol. 10:26.

 PubMed Web of Science ®Google Scholar

Park H, Kim K, Jang S, Park J, Cha H, Lee J, Kim J, Kim S, Lee C, Kim J. 2010. Attenuation of allergic airway inflammation and hyper-responsiveness in a murine model of asthma by silver nanoparticles. Int J Nanomed. 5:505–515.

 PubMed Web of Science ®Google Scholar

Su C, Chen T, Chang C, Chuang K, Wu C, Liu W, Ho K, Lee K, Ho S, Tseng H, et al. 2013. Comparative proteomics of inhaled silver nanoparticles in healthy and allergen-provoked mice. Int J Nanomed. 8:2783–2799.

 PubMedGoogle Scholar

Chuang H, Hsiao T, Wu C, Chang H, Lee C, Chang C, Cheng T. 2013. Allergenicity and toxicology of inhaled silver nanoparticles in allergen-provocation mice models. Int J Nanomed. 8:4495–4506.

 PubMed Web of Science ®Google Scholar

Xu Y, Tang H, Liu J, Wang H, Liu Y. 2013. Evaluation of the adjuvant effect of silver nanoparticles both in vitro and in vivo. Toxicol Lett. 219:42–48.

 PubMed Web of Science ®Google Scholar

Rossi E, Pylkkanen L, Koivisto AJ, Nykasenoja H, Wolff H, Savolainen K, Alenius H. 2010. Inhalation exposure to nanosized and fine TiO2 particles inhibits features of allergic asthma in a murine model. Particle Fibre Toxicol. 7:35.

 PubMed Web of Science ®Google Scholar

Jonasson S, Gustafsson A, Koch B, Bucht A. 2013. Inhalation exposure of nano-scaled titanium dioxide (TiO2) particles alters the inflammatory responses in asthmatic mice. Inhal Toxicol. 25:179–191.

 PubMed Web of Science ®Google Scholar

Gustafsson A, Jonasson S, Sandstrom T, Lorentzen J, Bucht A. 2014. Genetic variation influences immune responses in sensitive rats following exposure to TiO2 nanoparticles. Toxicology. 326:74–85.

 PubMed Web of Science ®Google Scholar

Mishra V, Baranwal V, Mishra R, Sharma S, Paul B, Pandey A. 2016. Titanium dioxide nanoparticles augment allergic airway inflammation and Socs3 expression via NF-κB pathway in murine model of asthma. Biomaterials. 92:90–102.

 PubMed Web of Science ®Google Scholar

Kim B, Lee P, Lee S, Park M, Jang A. 2017. Effect of TiO2 nanoparticles on inflammasome-mediated airway inflammation and responsiveness. Allergy Asthma Immunol Res. 9:257–264.

 PubMed Web of Science ®Google Scholar

Roy R, Kumar S, Verma AK, Sharma A, Chaudhari B, Tripathi A, Das M, Dwivedi P. 2014b. Zinc oxide nanoparticles provide an adjuvant effect to ovalbumin via a TH2 response in Balb/c mice. Int Immunol. 26:159–172.

 PubMed Web of Science ®Google Scholar

Roy R, Kumar D, Sharma A, Gupta P, Chaudhari B, Tripathi A, Das M, Dwivedi P. 2014a. ZnO nanoparticles induced adjuvant effect via toll-like receptors and Src signaling in Balb/c mice. Toxicol Lett. 230:421–433.

 PubMed Web of Science ®Google Scholar

Huang K, Lee Y, Chen H, Liao H, Chiang B, Cheng T. 2015. Zinc oxide nanoparticles induce eosinophilic airway inflammation in mice. J Hazard Mat. 297:304–312.

 PubMed Web of Science ®Google Scholar

de Haar C, Hassing I, Bol M, Bleumink R, Pieters R. 2006. Ultrafine but not fine particulate matter causes airway inflammation and allergic airway sensitization to co-administered antigen in mice. Clin Exp Allergy. 36:1469–1479.

 PubMed Web of Science ®Google Scholar

Yoshida T, Yoshioka Y, Fujimura M, Yamashita K, Higashisaka K, Morishita Y, Kayamuro H, Nabeshi H, Nagano K, Abe Y, et al. 2011. Promotion of allergic immune responses by intranasally-administrated nanosilica particles in mice. Nanoscale Res Lett. 6:195.

 PubMed Web of Science ®Google Scholar

Liu R, Yin L, Pu Y, Li Y, Zhang X, Liang G, Li X, Zhang J, Li Y, Zhang X. 2010. The immune toxicity of titanium dioxide on primary pulmonary alveolar macrophages relies on their surface area and crystal structure. J Nanosci Nanotechnol. 10:8491–8499.

 PubMed Web of Science ®Google Scholar

Hanley C, Thurber A, Hanna C, Punnoose A, Zhang J, Wingett D. 2009. The influences of cell type and ZnO nanoparticle size on immune cell cytotoxicity and cytokine induction. Nanoscale Res Lett. 4:1409.

 PubMed Web of Science ®Google Scholar

Marzaioli V, Aguilar-Pimentel J, Weichenmeier I, Luxenhofer G, Wiemann M, Landsiedel R, Wohlleben W, Eiden S, Mempel M, Behrendt H. 2014. Surface modifications of silica nanoparticles are crucial for their inert versus pro-inflammatory and immunomodulatory properties. Int J Nanomed. 9:2815–2832.

 PubMed Web of Science ®Google Scholar

Omlor AJ, Le DD, Schlicker J, Hannig M, Ewen R, Heck S, Herr C, Kraegeloh A, Hein C, Kautenburger R, et al. 2017. Local effects on airway inflammation and systemic uptake of 5-nm PEGylated and citrated gold nanoparticles in asthmatic mice. Small. 13:1603070.

 Web of Science ®Google Scholar

Vennemann A, Alessandrini F, Wiemann M. 2017. Differential effects of surface-functionalized zirconium oxide nanoparticles on alveolar macrophages, rat lung, and a mouse allergy model. Nanomaterials. 7:pii E280.

 Web of Science ®Google Scholar

Alessandrini F, Vennemann A, Gschwendtner S, Neumann A, Rothballer M, Seher T, Wimmer M, Kublik S, Traidl-Hoffmann C, Schloter M. 2017. Pro-Inflammatory versus immuno-modulatory effects of silver nanoparticles in the lung: Critical role of dose, size, and surface modification. Nanomaterials. 7:300–311.

 Web of Science ®Google Scholar

Seiffert J, Hussain F, Wiegman C, Li F, Bey L, Baker W, Porter A, Ryan M, Chang Y, Gow A, et al. 2015. Pulmonary toxicity of instilled silver nanoparticles: Influence of size, coating and rat strain. PloS One. 10:e0119726.

 PubMed Web of Science ®Google Scholar

Horie M, Stowe M, Tabei M, Kuroda E. 2015. Pharyngeal aspiration of metal oxide nanoparticles showed potential of allergy aggravation effect to inhaled ovalbumin. Inhal Toxicol. 27:181–190.

 PubMed Web of Science ®Google Scholar

Sandberg W, Låg M, Holme J, Friede B, Gualtieri M, Kruszewski M, Schwarze P, Skuland T, Refsnes M. 2012. Comparison of non-crystalline silica nanoparticles in IL-1β release from macrophages. Particle Fibre Toxicol. 9:1.

 PubMed Web of Science ®Google Scholar

Vandebriel R, Vermeulen J, van Engelen L, de Jong B, Verhagen L, de la Fonteyne-Blankestijn L, Hoonakker M, de Jong W. 2018. The crystal structure of titanium dioxide nanoparticles influences immune activity in vitro and in vivo. Part Fibre Toxicol. 15:9.

 PubMed Web of Science ®Google Scholar

Jeong J, Han Y, Poland C, Cho WS. 2015. Response-metrics for acute lung inflammation pattern by cobalt-based nanoparticles. Part Fibre Toxicol. 12:13.

 PubMed Web of Science ®Google Scholar

Cho W, Duffin R, Howie S, Scotton C, Wallace W, Macnee W, Bradley M, Megson I, Donaldson K. 2011. Progressive severe lung injury by zinc oxide nanoparticles; the role of Zn2+ dissolution inside lysosomes. Part Fibre Toxicol 8:27.

 PubMed Web of Science ®Google Scholar

Oh W, Kim S, Choi M, Kim C, Jeong Y, Cho B, Hahn J, Jang J. 2010. Cellular uptake, cyto-toxicity, and innate immune response of silica-titania hollow nanoparticles based on size and surface functionality. ACS Nano. 4:5301–5313.

 PubMed Web of Science ®Google Scholar

Murgia X, Pawelzyk P, Schaefer U, Wagner C, Willenbacher N, Lehr C. 2016. Size-limited penetration of nanoparticles into porcine respiratory mucus after aerosol deposition. Bio-macromolecules. 17:1536–1542.

 Google Scholar

Radauer-Preiml I, Andosch A, Hawranek T, Luetz-Meindl U, Wiederstein M, Horejs-Hoeck J, Himly M, Boyles M, Duschl A. 2016. Nanoparticle-allergen interactions mediate human allergic responses: Protein corona characterization and cellular responses. Particle Fibre Toxicol. 13:3.

 PubMed Web of Science ®Google Scholar

Winter M, Beer H, Hornung V, Kramer U, Schins R, Forster I. 2011. Activation of the inflammasome by amorphous silica and TiO2 nanoparticles in murine dendritic cells. Nanotoxicology. 5:326–340.

 PubMed Web of Science ®Google Scholar

Hamilton R, Buckingham S, Holian A. 2014. The effect of size on Ag nanosphere toxicity in macrophage cell models and lung epithelial cell lines is dependent on particle dissolution. Int J Mol Sci. 15:6815–6830.

 PubMed Web of Science ®Google Scholar

Vallhov H, Kupferschmidt N, Gabrielsson S, Paulie S, Strømme M, Garcia‐Bennett A, Scheynius A. 2012. Adjuvant properties of mesoporous silica particles tune the development of effector T cells. Small. 8:2116–2124.

 PubMed Web of Science ®Google Scholar

Lee C, Syu S, Chen Y, Hussain S, Aleksandrovich Onischuk A, Chen W, Steven Huang G. 2014. Gold nanoparticles regulate the blimp1/pax5 pathway and enhance antibody secretion in B-cells. Nanotechnology. 25:125103.

 PubMed Web of Science ®Google Scholar

Huang Y, Liu H, Xiong X, Chen Y, Tan W. 2009. Nanoparticle-mediated IgE-receptor aggregation and signaling in RBL mast cells. J Am Chem Soc. 131:17328–17334.

 PubMed Web of Science ®Google Scholar

Maurer-Jones M, Lin Y, Haynes C. 2010. Functional assessment of metal oxide nanoparticle toxicity in immune cells. ACS Nano. 4:3363–3373.

 PubMed Web of Science ®Google Scholar

Arai Y, Miyayama T, Hirano S. 2015. Difference in the toxicity mechanism between ion and nanoparticle forms of silver in the mouse lung and in macrophages. Toxicology. 328:84–92.

 PubMed Web of Science ®Google Scholar

Kapilevich L, Zaitseva T, Nosarev A, D'Iakova E, Petlina Z, Ogorodova L, Ageev B, Magaeva A, Itin V, Terekhova O. 2012. Influence of nanosize particles of cobalt ferrite on contractile responses of smooth muscle segment of airways. Ross Fiziol Zh Im Sechenova. 98:228–235.

 PubMedGoogle Scholar

Chen E, Garnica M, Wang Y, Chen C, Chin W. 2011. Mucin secretion induced by titanium dioxide nanoparticles. PloS One. 6:e16198.

 PubMed Web of Science ®Google Scholar