Loss of TET2 increases B-1 cell number and IgM production while limiting CDR3 diversity

Recent studies have demonstrated a role for Ten-Eleven Translocation-2 (TET2), an epigenetic modulator, in regulating germinal center formation and plasma cell differentiation in B-2 cells, yet the role of TET2 in regulating B-1 cells is largely unknown. Here, B-1 cell subset numbers, IgM production, and gene expression were analyzed in mice with global knockout of TET2 compared to wildtype (WT) controls. Results revealed that TET2-KO mice had elevated numbers of B-1a and B-1b cells in their primary niche, the peritoneal cavity, as well as in the bone marrow (B-1a) and spleen (B-1b). Consistent with this finding, circulating IgM, but not IgG, was elevated in TET2-KO mice compared to WT. Analysis of bulk RNASeq of sort purified peritoneal B-1a and B-1b cells revealed that heavy and light chain immunoglobulin gene expression was significantly reduced, predominantly in B-1a cells from TET2-KO mice compared to WT controls. As expected, the expression of IgM transcripts was the most abundant isotype in B-1 cells. Yet, only in B-1a cells was there a significant increase in the proportion of IgM transcripts in TET2-KO mice compared to WT. Analysis of the CDR3 of the BCR 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. V-D-J usage and circos plot analysis of V-J combinations showed enhanced usage of VH11 and VH12 pairings. Taken together, our study is the first to demonstrate that loss of TET2 increases B-1 cell number and IgM production and reduces CDR3 diversity, which could impact many biological processes and disease states that are regulated by IgM to self or other antigens. To investigate the role of global TET2-KO in function and BCR repertoire of different B cell subtypes.

已有研究证实，表观遗传调控因子十易位蛋白2（Ten-Eleven Translocation-2, TET2）可调控B-2细胞的生发中心形成与浆细胞分化，但目前关于TET2对B-1细胞的调控作用仍知之甚少。本研究以全身性敲除TET2的小鼠为模型，并以野生型（WT）小鼠作为对照，分析了B-1细胞亚群数量、免疫球蛋白M（IgM）产生情况以及基因表达谱。结果显示，与野生型小鼠相比，TET2全身性敲除（TET2-KO）小鼠的原发微环境腹膜腔中，以及骨髓（B-1a细胞）和脾脏（B-1b细胞）内的B-1a与B-1b细胞数量均显著升高。与上述结果一致，TET2-KO小鼠的循环IgM水平显著升高，而免疫球蛋白G（IgG）水平无明显变化。对分选纯化的腹膜腔B-1a、B-1b细胞进行批量RNA测序（bulk RNASeq）分析后发现，与野生型对照相比，TET2-KO小鼠的B-1a细胞中免疫球蛋白重链与轻链基因的表达显著下调，该现象在B-1a细胞中尤为突出。正如预期，在B-1细胞中，IgM转录本的表达丰度最高；但仅在B-1a细胞中，TET2-KO小鼠的IgM转录本占比相较于野生型小鼠显著升高。对B细胞受体（BCR）的互补决定区3（CDR3）进行分析后发现，TET2-KO小鼠B-1细胞中重复出现的CDR3序列丰度升高，且该现象在B-1a细胞中较B-1b细胞更为显著。对V-D-J基因片段使用偏好及V-J组合的环状图谱（circos plot）分析显示，VH11与VH12的配对使用频率显著升高。综上，本研究首次证实，TET2缺失可增加B-1细胞数量与IgM产生水平，并降低CDR3序列多样性，这可能影响诸多由IgM介导的针对自身抗原或其他抗原的生物学过程与疾病状态。本研究旨在探究全身性TET2敲除对不同B细胞亚群功能及B细胞受体库的调控作用。