β-1,3-glucan-lacking Aspergillus fumigatus mediates an efficient antifungal immune response by activating complement and dendritic cells

ABSTRACT

Complement system and dendritic cells (DCs) form – beside neutrophils and macrophages – the first line of defense to combat fungal infections. Therefore, we here studied interactions of these first immune elements with Aspergillus fumigatus lacking ß-1,3-glucans (fks1_tetOn^rep under repressed conditions) to mechanistically explain the mode of action of echinocandins in more detail. Echinocandins are cell wall active agents blocking β-glucan synthase, making the A. fumigatus fks1_tetOn mutant a good model to study immune-modulatory actions of these drugs. We now demonstrate herein, that complement was activated to significantly higher levels by the fks1-deficient strain compared to its respective wild type. This enhanced covalent linking of complement fragments to the A. fumigatus fks1_tetOn^rep mutant further resulted in enhanced DC binding and internalization of the fungus. Additionally, we found that fks1_tetOn^rep induced a Th1-/Th17-polarizing cytokine profile program in DCs. The effect was essentially dependent on massive galactomannan shedding, since blocking of DC-SIGN significantly reduced the fks1_tetOn^rep-mediated induction of an inflammatory cytokine profile.

Our data demonstrate that lack of ß-1,3-glucan, also found under echinocandin therapy, results in improved recognition of Aspergillus fumigatus by complement and DCs and therefore not only directly affects the fungus by its fungistatic actions, but also is likely to exert indirect antifungal mechanisms by strengthening innate host immune mechanisms.

Abbreviations: C: complement; CR:complement receptor; DC: dendritic cell; iDC: immature dendritic cell; DC-SIGN: Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin; ERK: extracellular signal–regulated kinases; JNK : c-Jun N-terminal kinases; MAPK: mitogen-activated protein kinase; NHS: normal human serum; PRR: pattern recognition receptor; Th :T helper; TLR :Toll-like receptor; WT: wild type.

KEYWORDS:

• Fungal infection
• dendritic cell
• complement
• T helper cells
• β-1
• 3-glucan

Acknowledgments

We thank our technician Karolin Thurnes, Dr. Michael Blatzer, Dr. Paul Hörtnagl and Dr Annelies Mühlbacher, Central Institute for Blood Transfusion & Immunological Department, Medical University of Innsbruck, Austria, for their valuable help and support regarding this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the Austrian Science Fund [W1253-B24 HOROS]; Christian Doppler Forschungsgesellschaft [CDL for Invasive Fungal Infections]; Oesterreichische Nationalbank [17633].