A functional BCR in human IgA and IgM plasma cells.

Plasma cells (PCs) are terminally differentiated cells of the B-cell lineage that secrete antibodies at a high rate and are thought to lack the expression of the B-cell receptor (BCR). Here, we report that human IgA and IgM, unlike IgG, PCs express a membrane functional BCR associated with the Igα/Igβ heterodimer. BCR cross-linking on IgA and IgM PCs led to Ca(2+) mobilization and extracellular signal-regulated kinase 1/2 and AKT phosphorylation and impacted survival of IgA PCs. These findings demonstrate a significant difference between human IgG, IgM, and IgA PCs and suggest that the IgA PC repertoire may be modulated by specific antigens with implications for the regulation of the mucosal immune system.