Molecular genetic features reflecting the preference for isotype switching to IgA expression by Peyer′s patch germinal center B cells

• Published in: International immunology 1991-12, Vol.3 (12), p.1253-1263
• Main Authors: Weinstein, Peter D., Schweitzer, Peter A., Cebra-Thomas, Judith A., Cebra, John J.
• Format: Article
• Language: English
• Subjects: germinal center(s); IgA; mRNA for IgA; Peyer′s patch(es); pre-plasmablasts
• ISSN: 0953-8178; 1460-2377
• DOI: 10.1093/intimm/3.12.1253

It has proven difficult to evaluate the functional potential of germinal center (GC) B cells, including those from Peyer′s patches (PP), by either in vivo or in vitro methods. Thus, rather than assess secreted Ig product as an indicator of functional potential we have instead sought to detect mRNAs related to the various Ig heavy chains in GC B cells from PP by in situ hybridization. We have found that the GCs of PP contain the vast majority of B cells with easily detectable levels of mRNAα. These levels are intermediate between those of small resting B cells and plasmablasts. When PP B cells are enriched for cells bearing GC markers, ∼50% contain mRNAα and 40% mRNAα. Similar enrichment for sigA+ B cells gave 50% of cells with easily detectable mRNAα and few if any positive for mRNAμ. The sizes of these mRNAs were similar to those encoding the membrane and secretory form of μ and α chains. No Cα germ-line transcripts could be detected by Northern analyses using a probe for sequences 5′ to the α switch regions. Finally, GC and slgA+ cells from PP also showed the absence of a portion of their genomic DNA for CH genes 5′ of Cα. Thus, it seems likely that most of the GC cells expressing mRNAα have undergone conventional VDJ recombination to Cα at the DNA level in order to switch to the expression of IgA. Our findings reflect the extraordinary preference for switching to IgA by GC cells in PP.