Brief Report IMMUNOBIOLOGY A functional BCR in human IgA and IgM plasma cells

B cells express clonotype-specific surface immunoglobulins (Ig’s), which associate to the Iga/Igb heterodimer to constitute the B-cell receptor (BCR). Binding of the specific antigen to the BCR triggers a signaling cascade that leads, in concert with other signals, to cell activation, proliferation, and generation of memory B cells and plasma cells (PCs). BCR expression is required for the survival of memory B cells but is thought to be lost on mature PCs due to a secretory switch in the Ig messenger RNA (mRNA). Long-lived PCs persist in bone marrow (BM) and, in the case of IgA PCs, in mucosal tissues, homing to specific niches and continually secreting antibodies, thus maintaining serological memory. Serum IgG antibodies and consequently IgG PCs can persist for a lifetime, although displacement by newly generated PCs and susceptibility to Fcg Receptor IIB-mediated apoptosis increase their turnover. In contrast, the IgA PCs present in the lamina propria (LP) show a high turnover rate. These findings suggest different mechanisms of regulation of IgG and IgA PCs.