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.