Concanavalin A-induced B-cell proliferation mediated by allogeneically derived helper factors

Highly purified, small, resting murine Ig-positive spleen cells could be induced to proliferate by concanavalin A (Con A) if the activation was supported by allogeneic helper factors (AHF). Con A or AHF alone was unable to induce cell proliferation as determined by incorporation of [methyl-3H] thymidine. However, if AHF produced by a mixed lymphocyte culture was present together with Con A, the B lymphocytes were strongly activated exhibiting a stimulation index of approximately 2000 as compared to Con A alone. The dose-response maximum was obtained after a 4-day culture using 25% of a supernatant from a mixed lymphocyte culture as a source of AHF. The kinetics of the AHF-supported B-cell activation was also investigated. The activation could be completely inhibited by the addition of 100 mM methyl alpha-D-mannopyranoside at the initiation of the culture, but, if added 14-18 hr later, the cells have had the necessary induction period and a proliferation could be recorded. AHF had to be present at the initiation of the cultures, otherwise the response immediately diminished, whereas Con A could be added up to 6 hr after initiation without affecting the proliferative response.