Comparative characteristics of mu chain and alpha chain transcripts expressed by individual tonsil plasma cells

Plasma cells (PCs) are one of the two major cell types generated during germinal center reactions. To test the hypothesis that PCs express a unique repertoire of immunoglobulin (Ig) genes resulting from intensive antigenic stimulation and selection, the mutational pattern and distribution of V(H) gene segments within 178 transcripts amplified from individual IgM and IgA secreting tonsil PCs were analyzed. The results demonstrated that both mu and alpha transcripts expressed repertoires with limited diversity. Moreover, both mu and alpha transcripts were heavily mutated, with a significantly increased mutational frequency noted for alpha compared to mu transcripts (5.0 x 10(-2) vs 1.8 x 10(-2), P<0.001). In addition, both mu and alpha transcripts showed significantly greater targeting of mutations to RGYW motifs (purine/guanine/pyrimidine/A or T) compared to memory B cells. Finally, clonally expanded cells were detected in alpha but not mu PC compartments. These results indicate that antigen driven stimulation and selection shape the entire expressed PC repertoire, but the impact is greater in alpha expressing PCs.