In vitro antigen-mediated clonal expansion of memory B lymphocytes.

An in vitro model for the propagation and expansion of the memory B lymphocyte population is described. DNP-BGG immune cells were mixed with OVA immune cells and challenged immediately with DNP-OVA. After the 1st response had begun to wane, the cells were rechallenged with DNP-OVA (day 11 of culture). An average of 13-fold more PFC were observed after delayed challenge (day 11). This expansion in the PFC response was an antigen-dependent process and did not involve recruitment of new memory cells from the virgin lymphocyte pool. The level of expansion of the memory cell pool was also calculated using limiting dilution analysis and was found to fall in a range of 16- to 67-fold increase in precursor frequency. In addition to the expansion of the memory B cell population, we also observed the development of 2 immunoregulatory cycles previously observed only in vivo. First, in the presence of persistent antigen, a cyclical PFC response was seen. Second, after day 10 of culture, optimal PFC numbers were observed only when DNP-lysine was added to the plaque assay. Such hapten-augmentable PFC responses have been reported by other investigators as indicative of anti-idiotypic regulation. This possibility is examined more extensively in the following communication.