Analysis of the antigen-induced in vitro differentiation of human peripheral blood B cells: stimulation with ovalbumin induces the transition from the resting state into the excited state.

Human peripheral blood B lymphocytes, when cultured for 6 days with ovalbumin in the presence of T cells and monocytes, can differentiate into plaque-forming cells (PFC) secreting small amounts of antigen-specific IgM. Phenotype analysis using Ig-isotype and B-cell specific monoclonal antibodies revealed that the PFC precursor is a sIgM+ IgD+IgG- B lymphocyte. The PFC itself also carries the B-cell specific membrane antigens B1 and BA-1; it expresses only IgM on its surface. When apart from the antigen a Concanavalin A-induced, T-cell derived growth factor preparation was added to the cultures, we observed the disappearance of sIgM from the membrane. Furthermore, it was demonstrated by means of density gradient centrifugation that the differentiation of the PFC-precursor into a PFC is accompanied by a decrease in cellular density. Finally, it was shown using hydroxyurea as an inhibitor of DNA-synthesis, that the PFC-precursor passes several cycles of cell division during the process of differentiation into a PFC.