RESTRICTION OF GENE EXPRESSION IN B LYMPHOCYTES AND THEIR PROGENY : III. Endogenous IgA and IgM on the Membranes of Different Plasma Cell Precursors

Fluorescent antibody staining with antibodies to the f and g locus allotype markers present on rabbit α-chains revealed that the α-chain is the heavy chain on the Peyer's patch lymphocytes which previously had been shown to be the precursors of IgA-producing plasma cells. In addition, lymphocytes which had been stripped of membrane Ig with pronase and then cultured overnight to allow the sole expression of endogenous membrane Ig were found to have either the µ-chain or the α-chain on their membranes, but not both. These results suggest that most lymphocytes are restricted to the synthesis of one class of heavy chains at a time and that the commitment to synthesizing that particular heavy chain is maintained during the differentiation of lymphocytes into plasma cells. The proportion of lymphocytes with membrane α-chains is higher in the Peyer's patch and appendix, two gut-associated lymphoid tissues (GALT), than in other lymphoid tissues. Since the GALT are enriched sources of precursors for IgA-producing plasma cells compared to nongut-associated tissues, the presence of cells bearing membrane α-chains correlates well with the relative abilities of these tissues to generate IgA plasma cells.