Expression of CD40L on CD8 T cells and its role in influenza A infection (IRC5P.618)

Abstract

CD8 T cells play an important role in protective immunity against a wide range of pathogens and the factors that control their activation are clearly important. CD40L-mediated CD40 licensing of dendritic cells by CD4 T cells is known to be necessary for the generation of a robust CD8 T cell response. Less clear is the contribution of CD40L on CD8 T cells to their activation. We have previously shown that CD8 T cells are able to induce the production of IL-12 p70 by dendritic cells in a CD40L-dependent manner. To better understand the role of CD40L on CD8 T cells responses, we generated and characterized CD40L-expressing CD8 T cells both in vitro and in vivo. We found that CD40L is expressed on 30-50% of activated effector CD8 T cells and the differentiation of CD8 T cells into CD40L-expressing cells is strongly induced by IL-12, suggesting the presence of a positive feedback mechanism mediated by CD40L and IL-12. Using an influenza A mouse model, we examined whether this mechanism is involved in the primary expansion of CD8 T cells during an infection and whether CD40L-expressing CD8 T cells are able to license dendritic cells for optimal memory CD8 T cell programming. In the absence of CD40L signaling, the ability to upregulate CD25 and downregulate CD62L is diminished in CD8 T cells, causing an impairment in their primary expansion and also their ability to accumulate at the site of infection.