Functional characterization of mouse lymphocyte subpopulations identified by their natural binding of bacteria. I. Identification of the Ig-secreting cell subpopulation.

Three mouse B cell subpopulations (B1, B2 and B3) can be identified by their natural binding of bacteria. To determine whether these subpopulations have unique functions, we assayed the number of anti-SRBC-secreting cells and the number of Ig-secreting cells in unseparated populations and in populations in which the B2 and B3 cells were removed by immobilized monolayers of Escherichia coli-2, a bacteria that binds B2 and B3 cells. Essentially all of the plaque forming cells present in the unseparated population were found in the B1-enriched population, suggesting that most of the antibody-secreting and Ig-secreting cells were in the B1 subpopulation. To show conclusively that the anti-SRBC-secreting cells resided in the B1 subpopulation, the Jerne plaque assay was performed on slides by using lymphocytes prelabeled with various bacteria and the cells that gave rise to the plaques were directly examined. Essentially all of the secreting cells were labeled with Corynebacterium xerosis, which binds to the B1 and B2 cells, whereas very few of the secreting cells were labelled with Arizona hinshawii, which binds to the B2 cells, or with Escherichia coli-2, which binds to the B2 and B3 cells. Thus, the B1 subpopulation contained essentially all of the antibody-secreting cells, which indicates that the B cell subpopulations identified by bacteria are functionally different.