Activated B cells that differentiate into plasmablast downregulate the CD23 marker and IL4 pathway, after an initial IL4 response.
CD23-negative cells, which are pre-plasmablasts, also loose CBLB expression and increase IRF4 levels to promote plasmablast differentiation
The terminal differentiation of B cells into antibody-secreting cells (ASCs) is a critical component of adaptive immune responses. However, it is a very sensitive process, which dysfunctions lead to a great variety of lymphoproliferative neoplasia including germinal center-derived lymphomas. To better characterize the late genomic events driving the ASC differentiation of human primary naive B cells, we used our in vitro differentiation system and a combination of RNA sequencing with ATAC-seq. Our results evidenced two mechanisms driving human terminal B cell differentiation. Firstly, after an initial response to IL-4, cells that committed to an ASC fate downregulated the CD23 marker and IL-4 signaling, whereas cells that maintained IL-4 signaling did not differentiate. Secondly, human CD23-negative cells also increased IRF4 protein to levels required for ASC differentiation, but independently of the ubiquitin-mediated degradation process previously described in the mouse. Finally, we showed that CD23-negative cells (i) carried the imprint of their previous activated B-cell status, (ii) were precursors of plasmablasts, and (iii) had a similar phenotype to in vivo pre-plasmablasts. Altogether, our results provide an unprecedented genomic characterization of the fate decision between activated B cells and plasmablast, which gives new insights in pathological mechanisms driving lymphoma biology.