FIGURE 2

Costimulatory signals for class switch recombination (CSR) to IgA. BAFF and APRIL are expressed by dendritic cells, monocytes, and human colonic epithelial cells (following Toll-like receptor signaling, not shown), whereas APRIL can also be secreted by macrophages and activated T cells. These cytokines bind to their receptors, BAFF-R, TACI, or BCMA, which are all expressed by B cells. APRIL, A proliferation-inducing ligand; BAFF, B-cell activating factor of the TNF family; BCMA, B-cell maturation antigen; TACI, transmembrane activator and CAML interactor.