Loss of TET2 Increases B-1 Cell Number and IgM Production While Limiting CDR3 Diversity

Ten-Eleven Translocation-2 (TET2) is an epigenetic modifier and potent regulator of immune cells, yet its role in B-1 cell biology is largely unknown. B-1 cells protect against infection and clear apoptotic cells via the production of natural Immunoglobulin M (IgM). Our study analyzed B-1 cell subsets from mice with global knockout (KO) of TET2 compared to wildtype (WT) controls using flow cytometry to determine the frequency and number of B cell subsets, RNA sequencing to determine differences in global gene expression as well as B cell receptor (BCR) repertoire analysis, and enzyme-linked immunosorbent assay (ELISA) to evaluate plasma IgM levels. Mice with TET2-KO had elevated numbers of B-1a and B-1b cells in their primary niche, the peritoneal cavity, as well as in the bone marrow and spleen. Consistent with this finding, circulating IgM was elevated in TET2-KO mice compared to WT. We observed reduced expression in both heavy and light chain immunoglobulin genes, predominantly in B-1a cells from TET2-KO mice compared to WT controls. As expected, IgM was by far the most abundant isotype expressed by genes in B-1 cells. Yet, only in B-1a cells was there a significant increase in the proportion of IgM isotypes in TET2-KO mice compared to WT. Analysis of the complementarity determining region 3 (CDR3) revealed an increased abundance of replicated CDR3 sequences in B-1 cells from TET2-KO mice, which was more clearly pronounced in B-1a compared to B-1b cells. The results from our study suggest that TET2 may regulate the pool of antigen-specific IgM-producing cells.