CD4 and type 1 diabetes mellitus: To date, the role for B cells in T1D progression has been linked to their peripheral APC function—their ability to present β cell antigens to β-reactive CD4+ T cells (28) enhances CD4+ T helper cell activation of CD8+ T cells, and in islets B cells provide survival signals for activated CD8+ T cells enabling a sustained cytotoxic attack on β cells (29).