CD40 function in immune development and response: Cell type requirements and cytoplasmic domain function

Abstract

Abstract CD40 is a TNFR family member and serves as a costimulatory molecule expressed on multiple antigen presenting cell (APC) lineages. The functional significance of CD40 expression is illustrated by human disease and mouse models of life-threatening immune deficiency. CD40-CD40L deficiency affects multiple aspects of immune development and response. However, cell type-specific requirements for CD40 and requirements for CD40 signaling domains have not been comprehensively analyzed. In this study, we use conditional CD40 knockout mice to study cell type requirements and generated CD40 intracellular domain mutants by CRISPR to determine domain-specific functions. CD40 expression on B cells but not DC is required for CD40 dependent superantigen-specific negative selection and for T-cell dependent class-switched antibody responses. TRAF2/3 binding domains of CD40 are critical for these CD40 functions, while deletion of putative TRAF6 binding domain had minimal effect. In contrast, in vivo priming of cytokine-producing T cells depends on CD40 expression on DC but not B cells and requires both TRAF2/3 and TRAF6 domains. CD40 expression on both B cells and DC is required for maximal autoimmune EAE disease induced by recombinant human MOG (rhMOG), and both TRAF2/3 and TRAF6 domains of CD40 are required for this autoimmune response. Initial results indicate that CD40 on thymic epithelial cells and DC contributes to negative selection of tissue restricted antigen-binding T cells. These results identify different CD40-dependent APC requirements and suggest distinct CD40 signaling pathways for specific immune responses. Analysis of the linkage between cell type-specific CD40 function and intracellular signaling is under study.