Cooperation between platelet-derived CD154 and CD4+ T cells for enhanced germinal center formation

It has been demonstrated previously that platelet‐derived CD154 communicates with the adaptive immune compartment, enhancing B and T cell responses in CD154−/− mice. The presence of platelets was also shown to be necessary for optimal production of immunoglobulin G (IgG) in normal C57BL/6 mice. These data led us to hypothesize that platelets perform a sentinel function, quickly relaying activating signals to the adaptive immune compartment. Here, we report that platelet‐derived CD154 increases serum IgG levels and germinal center formation under conditions where antigen‐specific CD4+ T cell numbers are limiting. We propose that in the physiologic setting where antigen‐specific B and T cells are rare, platelets function to enhance signals required for robust adaptive humoral immunity.