CD40 and atherosclerosis: The primary costimulatory ligand by which TFH cells provide help to activated B cells is CD40L, and ligation of its receptor CD40 in B cells is required for GC responses against T cell–dependent protein antigens.39 Using a mixed BM Ldlr−/− chimera model, Tay et al10 found B cell–selective CD40 deletion decreased TFH and GC B cells without changing IgM levels, leading to decreased early atherosclerosis in comparison to nonlittermate WT mice.