Effect of chlorpromazine on the in vitro immune response

The effect of chlorpromazine at concentrations from 10(-7) to 5 X 10(-5)M on the in vitro plaque-forming cell responses to sheep erythrocytes was tested. If CPZ was present in cultures during the whole incubation period, concentrations of CPZ more than 5 X 10(-6)M inhibited the PFC responses, whereas concentrations between 5 X 10(-7) and 5 X 10(-6)M had a slightly enhancing effect. If a defined concentration of CPZ (1.3 or 1.5 X 10(-5)M) was added to cultures for a brief period of time (12 or 24 h) at various intervals after the initiation of culture and antigenic stimulation, PFC responses were inhibited most effectively during the first brief periods of incubation. The later the drug was added, the more the extent of inhibition decreased. On the other hand, CPZ had no effect or a slightly enhancing effect when added in the very late period (72--95 h) of incubation. These findings suggest that the observed immunosuppression could be attributed mainly to the impairment of early cellular events, presumably cell interaction events, preceding the process of DNA synthesis and cell proliferation of antibody-forming cells and their precursors.