Summary
The overall picture of IgA B cell differentiation to emerge from these studies is that sIgM-bearing ‘virgin’ B cells entering the Peyer's patches are subject to a microenvironment (most probably organ-specific stromal cells) which brings about initial or primary IgA switch differentiation. For reasons mentioned, this probably does not involve TGF-β, which instead appears to operate on a cell, such as the CH12.LX B cell, which has already undergone the initial steps of IgA isotype switching. The next stage of IgA B cell differentiation involves a cell which expressed both sIgM and sIgA simultaneously and appears to produce Cμ and Cα mRNA transcripts in the absence of a deletional rearrangement. Whether this involves a ‘transplicing’ mechanism or some other mechanism has yet to be determined. Finally, committed IgA B cells emerge from teh dual-bearing cell population which express only sIgA. These cells can migrate out of Peyer's patches and respond to various terminal differentiation factors such as IL-5, Il-6 and IFN-γ.
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Strober, W., Harriman, G.R. & Kunimoto, D.R. Early steps of IgA B cell differentiation. Immunol Res 10, 386–388 (1991). https://doi.org/10.1007/BF02919726
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DOI: https://doi.org/10.1007/BF02919726