B Cells and TCR Avidity Determine Distinct Functions of CD4+ T Cells in Retroviral Infection

Abstract

The T cell-dependent B cell response relies on cognate interaction between B cells and CD4+ Th cells. However, the consequences of this interaction for CD4+ T cells are not entirely known. B cells generally promote CD4+ T cell responses to pathogens, albeit to a variable degree. In contrast, CD4+ T cell responses to self- or tumor Ags are often suppressed by B cells. In this study, we demonstrated that interaction with B cells dramatically inhibited the function of virus-specific CD4+ T cells in retroviral infection. We have used Friend virus infection of mice as a model for retroviral infection, in which the behavior of virus-specific CD4+ T cells was monitored according to their TCR avidity. We report that avidity for Ag and interaction with B cells determine distinct aspects of the primary CD4+ T cell response to Friend virus infection. Virus-specific CD4+ T cells followed exclusive Th1 and T follicular helper (Tfh) differentiation. High avidity for Ag facilitated expansion during priming and enhanced the capacity for IFN-γ and IL-21 production. In contrast, Tfh differentiation was not affected by avidity for Ag. By reducing or preventing B cell interaction, we found that B cells promoted Tfh differentiation, induced programmed death 1 expression, and inhibited IFN-γ production by virus-specific CD4+ T cells. Ultimately, B cells protected hosts from CD4+ T cell-mediated immune pathology, at the detriment of CD4+ T cell-mediated protective immunity. Our results suggest that B cell presentation of vaccine Ags could be manipulated to direct the appropriate CD4+ T cell response.