Inhibition of antigen-induced B lymphocyte activation in vitro by cytochalasin B

Cytochalasin B (CB), a fungal metabolite which disrupts microfilaments. and will inhibit capping and other events requiring membrane movement, suppressed the production of antibody-forming cells (AFC) in both mouse whole spleen cultures immunized with sheep erythrocytes (SRBC) and in mouse B lymphocyte cultures immunized with the thymic independent antigen DNP-Ficoll (DF). CB at a concentration of 1 mug/ml inhibited the AFC response by more than 90% in spleen cell cultures immunized with SRBC. This inhibition was completely reversible by removal of CB up to 24 hr after the start of culture. Spleen cells cultured in the presence of CB for the first 48 to 72 hr had a decreased AFC response similar to that of cultures in which SRBC had been withheld for thocyte the same period of time. Incubating whole spleen cell or B lymphocyte cultures immunized with DF for as short as 6 hr decreased the AFC response more than 60%. Antibody secretion, cell viability, and antigenicity of the SRBC and DF were not affected by CB. The results of these experiments favor the concept that movement of surface receptors is necessary in activating lymphocytes to differentiate into AFC. The differential response to CB observed in SRBC and DF stimulated cultures makes the technique employed a useful tool to study membrane events occuring between antigen interaction with surface receptor and the initiation of differentiative events.