IL-10 Production in Murine IgM CD138 Cells is Driven by Blimp-1 and Downregulated in Class-switched Cells

In contrast to antibody-induced inflammatory responses, some B-cell subpopulations suppress inflammation through the production of interleukin (IL)-10. However, the mechanisms underlying Il10 gene expression during B-cell development is elusive. Here, we identify IgM B220 CD138 cells responsible for marked IL-10 production in the bone marrow and spleen of mice. These murine IL-10-producing cells predominantly secrete IgM and have unique characteristics of long-lived plasma cells in spite of high expression of surface IgM. We found that IL-10 production is strongly correlated with the expression level of Prdm1 (encoding the Blimp-1 protein), an essential regulator of plasma cell development. Furthermore, overexpression of Prdm1 induces Il10 expression in naïve B cells. Immunoglobulin class-switching recombination events resulted in the downregulation of both Il10 and Prdm1 expression in differentiating B cells. Thus, the prolonged elevation of Blimp-1 expression during the formation of IgM CD138 cells without class-switching elicits IL-10 production. Adoptive transfer of Il10-deficient B cells into B-cell-deficient mice demonstrated that IgM CD138 cell-derived IL-10 supports the survival of class-switched plasma cells and their antibody production in response to antigen challenge. These findings reveal an important role for IL-10 secretion by IgM CD138 cells in the complete and efficient humoral response.