Characterization of human IgA+ memory B cells using spectral flow cytometry and bulk transcriptomic analysis

IgA is the most produced immunoglobulin by the human body, mainly in secretions at mucosal surface and exerts important functions of activation and regulation of immune system. Despite its importance, the phenotype of circulating IgA+ B cells is remains poorly described. Here, we deeply explored the phenotype of IgA+ memory B cells compared to IgG+ memory B cells from healthy donors using spectral flow cytometry. A bulk transcriptomic analysis was performed on isolated IgA+ and IgG+ memory B cells. While IgA+ memory B cells expressed moreincrease d levels of a variety of gut homing markers (CCR9, CCR10, integrin a4ß7) and CD11b, and GPR183, whereas IgG+ memory B cells expressed more CXCR3, CXCR4 and VLA4 at protein level. Three other markers were discriminant: CD43 and PD-L1, more expressed by IgA+ memory B cells and CD25 by IgG+ memory B cells. At the RNA level, we confirmed the overexpression of CD11b in IgA+ memory B cells. Interestingly, the transcription factor RUNX2 was dominant in IgA+ memory B cells whereas Tbet was overexpressed in IgG+ memory B cells The mRNA ARHGAP20 was upregulated in IgA+ memory B cells and miR4432 was associated to IgG+ memory B cells. Altogether, we showed specific markers of blood IgA+ memory B cells and we hope that this approach will allow for a deeper understanding of IgA+ B cell biology.

免疫球蛋白A（IgA）是人体产生量最多的免疫球蛋白（immunoglobulin），主要分布于黏膜表面的分泌物中，在免疫系统的激活与调控过程中发挥关键作用。尽管IgA具备重要生物学意义，但循环IgA+ B细胞的表型仍未得到充分描述。本研究借助光谱流式细胞术（spectral flow cytometry），对比健康供体来源的IgA+记忆B细胞与IgG+记忆B细胞，深入探究了二者的表型差异。研究团队对分离得到的IgA+与IgG+记忆B细胞开展了批量转录组学分析。在蛋白表达层面，IgA+记忆B细胞高表达多种肠道归巢标志物（CCR9、CCR10、整合素α4β7）、CD11b以及GPR183；而IgG+记忆B细胞则高表达CXCR3、CXCR4与VLA4。另有三种标志物可用于区分两类细胞：IgA+记忆B细胞高表达CD43与PD-L1，IgG+记忆B细胞则高表达CD25。在RNA转录水平上，本研究证实了IgA+记忆B细胞中CD11b的过表达现象。值得关注的是，转录因子RUNX2在IgA+记忆B细胞中表达占优，而Tbet则在IgG+记忆B细胞中呈高表达状态。ARHGAP20的mRNA在IgA+记忆B细胞中上调，miR4432则与IgG+记忆B细胞密切相关。综上，本研究明确了血液IgA+记忆B细胞的特异性标志物，我们期望该研究方法能够为深入解析IgA+ B细胞的生物学特性提供助力。