CD40LG and infection: Physiological roles of mA3 protein in GC B cells are currently unknown; however, B cells have long been implicated as a reservoir of persistent Friend retrovirus infection [43] and recent analyses utilizing a newly developed fluorescent virus revealed that follicular B cells are initially infected with FV in the acute phase and the infection persisted in IgM−, IgD− class-switched B cells in late phase [44].