Follicular Helper T Cell Differentiation Requires Continuous Antigen Presentation that Is Independent of Unique B Cell Signaling

Effective humoral immunity depends on the support of B cell responses by T follicular helper (Tfh) cells. Although it has been proposed that Tfh cell differentiation requires T-B interactions, the relative contribution of specific populations of Ag-presenting cells remains unknown. We employed three independent strategies that compromised interactions between CD4 + T cells and activated B cells in vivo. Whereas the expansion of CD4 + T cells was relatively unaffected, Tfh cell differentiation was completely blocked in all scenarios. Surprisingly, augmenting antigen presentation by non-B cells rescued Tfh cell differentiation, as determined by surface phenotype, gene expression, and germinal center localization. We conclude that although Ag presentation by responding B cells is typically required for the generation of Tfh cells, this does not result from the provision of a unique B cell-derived signal, but rather because responding B cells rapidly become the primary source of antigen. [Display omitted] ► SAP deficiency impairs Tfh cell development ► Lack of Ag presentation by activated B cells impairs Tfh cell development ► Ag presentation by DCs is short-lived ► Prolonging Ag presentation by DCs abolishes the need for B cells in Tfh cell development