In vitro immune response of human peripheral lymphocytes. V. PHA- and protein A-induced human B colony formation and analysis of the subpopulations of B cells.

Human B colony formation was observed with PHA or protein A as a mitogen. Preculture of B cells with mitogens in the presence of irradiated T cells for 3 days was a prerequisite for the induction of B cell colonies. About 300 to 700 colonies per 10(6) seeded cells were detected and a linear relationship between the number of cells seeded and the number of colonies developed was observed. Cells in PHA-induced colonies had surface IgM and/or IgD but no cytoplasmic Ig, whereas cells recovered from protein A-induced colonies had cytoplasmic Igs that were not only IgM but IgG and IgA. In each of the protein A-induced colonies, a sequential appearance of IgM-, IgG-, and IgA-producing cells was observed from day 3 to day 5, showing that IgM-, IgG-, and IgA-producing cells were derived from a single precursor cell. PHA and protein A had an additive effect on the number of colonies induced. About 50% of colonies induced in the presence of both PHA and protein A had Ig-producing cells. These results suggest that PHA and protein A may stimulate distinct subsets of B cells into colony formation.