Secreted IgM modulates the pool of IL-10 producing B Cells

Regulatory B cells (Bregs) are critical for maintaining immune tolerance, and alterations in Breg numbers has detrimental effects in inflammatory diseases, infection, and cancer. Bregs are found among most B cell subsets and act primarily by producing IL-10. Despite their importance, the signals that control Breg differentiation and maintenance are not well defined. Here, we demonstrate that mice incapable of secreting IgM (sIgM−/−) have drastically increased IL-10+ Bregs in lymphoid organs compared to wildtype (WT) mice. These IL-10+ Bregs are polyclonal and increased among all major B cell subsets. While newborn WT mice ( Supported by grants from NIH (T32AI134646, R01AR067751, R01AI127389, R01AI148652)