Active CD4⁺ helper T cells directly stimulate CD8⁺ cytotoxic T lymphocyte responses in wild-type and MHC II gene knockout C57BL/6 mice and transgenic RIP-mOVA mice expressing islet β-cell ovalbumin antigen leading to diabetes

Abstract

CD4⁺ helper T (Th) cells play crucial role in priming, expansion and survival of CD8⁺ cytotoxic T lymphocytes (CTLs). However, how CD4⁺ Th cell's help is delivered to CD8⁺ T cells in vivo is still unclear. We previously demonstrated that CD4⁺ Th cells can acquire ovalbumin (OVA) peptide/major histocompatibility complex (pMHC I) and costimulatory CD80 by OVA-pulsed DC (DC_OVA) stimulation, and then stimulate OVA-specific CD8⁺ CTL responses in C57BL/6 mice. In this study, we further investigated CD4⁺ Th cell's effect on stimulation of CD8 CTL responses in major histocompatibility complex (MHC II) gene knockout (KO) mice and transgenic rat insulin promoter (RIP)-mOVA mice with moderate expression of self OVA by using CD4⁺ Th cells or Th cells with various gene deficiency. We demonstrated that the in vitro DC_OVA-activated CD4⁺ Th cells (3 × 10⁶ cells/mouse) can directly stimulate OVA-specific CD8⁺ T-cell responses in wild-type C57BL/6 mice and MHC II gene KO mice lacking CD4⁺ T cells. A large amount of CD4⁺ Th cells (12 × 10⁶ cells/mouse) can even overcome OVA-specific immune tolerance in transgenic RIP-mOVA mice, leading to CD8⁺ CTL-mediated mouse pancreatic islet destruction and diabetes. The stimulatory effect of CD4⁺ Th cells is mediated by its IL-2 secretion and CD40L and CD80 costimulations, and is specifically delivered to OVA-specific CD8⁺ T cells in vivo via its acquired pMHC I complexes. Therefore, the above elucidated principles for CD4⁺ Th cells will have substantial implications in autoimmunity and antitumor immunity, and regulatory T-cell-dependent immune suppression.

• CD4⁺ Th
• pMHC I
• dendritic cells
• membrane acquisition
• diabetes

Abbreviations
DC	=	dendritic cells
DCOVA	=	OVA-pulsed DC
FITC	=	fluorescein isothiocyanate
PE	=	R-phycoerythrin
TCR	=	T-cell receptor
DMEM	=	Dulbecco's modified eagles medium
pMHC I	=	peptide/major histocompatibility complex
OT-I	=	OVA-specific class I-restricted TCR transgenic
OT-II	=	OVA-specific class II-restricted TCR transgenic
RIP	=	rat insulin promoter
Th	=	helper T-cell
CFES	=	cardoxyfluorescein diacetate succinimidyl ester
CTL	=	cytotoxic T lymphocyte
CFA	=	complete Freund's Adjuvant

Abbreviations
DC	=	dendritic cells
DCOVA	=	OVA-pulsed DC
FITC	=	fluorescein isothiocyanate
PE	=	R-phycoerythrin
TCR	=	T-cell receptor
DMEM	=	Dulbecco's modified eagles medium
pMHC I	=	peptide/major histocompatibility complex
OT-I	=	OVA-specific class I-restricted TCR transgenic
OT-II	=	OVA-specific class II-restricted TCR transgenic
RIP	=	rat insulin promoter
Th	=	helper T-cell
CFES	=	cardoxyfluorescein diacetate succinimidyl ester
CTL	=	cytotoxic T lymphocyte
CFA	=	complete Freund's Adjuvant

Acknowledgements

This work was supported by research grants (MOP 79415 and 81228) from the Canadian Institute of Health Research (CIHR). Zhenmin Ye was supported by Postdoctoral Fellowship of Saskatchewan Health Research Foundation.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.