Expression of <scp>RAG</scp> and secondary gene rearrangement of <scp>BCR</scp> in mature peripheral B lymphocytes in <scp>Takayasu</scp> arteritis

To evaluate the expression of recombinant activating gene (RAG) and B cell receptor (BCR) gene rearrangements in mature peripheral B lymphocytes in Takayasu arteritis (TA) to explore the possible mechanism of humoral immune response in TA. Ten patients with TA and 10 age- and sex-matched healthy volunteers (control group) from Beijing Shijitan Hospital, Capital Medical University and Peking Union Medical College Hospital, between 2022 and 2023, were included in this study. The mRNA of the RAG was measured using real-time quantitative PCR (RT-PCR). Western blotting was used to detect RAG protein expression levels. NGS technology was used to detect BCR gene rearrangement. The mRNA expression level of RAG1 and RAG2 in peripheral mature B lymphocytes in patients with TA was significantly higher than in the control group (RAG1 5.56 ± 1.71 vs. 1.94 ± 0.86, p < 0.05; RAG2 5.26 ± 1.59 vs. 1.65 ± 0.64, p < 0.05), respectively. The protein expression level of the RAG1 and the RAG2 in peripheral mature B lymphocytes in patients with TA was significantly higher than in the healthy control group (RAG1 4.33 ± 1.58 vs. 1.52 ± 0.59, p < 0.001; RAG2 4.67 ± 1.88 vs. 1.59 ± 0.56, p < 0.001). The number of peripheral B lymphocyte BCR clonotypes in the group of patients with TA was significantly higher than in the normal control group (1574 ± 317.7 vs. 801.3 ± 202.1, p < 0.05). The abundance of IGHV clones in patients with TA was higher than in the normal control group (31.185% vs. 13.449%), which was positively correlated with the expression levels of RAG1 and RAG2 (correlation coefficient r = 1.00, p < 0.001), respectively. High expression of the RAG gene coexists with secondary BCR gene rearrangement in mature peripheral B lymphocytes in patients with TA, providing important clues regarding the potential humoral response in TA; however, further studies with larger samples are needed.