Stimulation of cAMP levels and modulation of antibody formation in mice immunized with cholera toxin.

Injection of mice with 1.0 mu g of a purified exotoxin derived from Vitro cholerae together with a challenge injection of sheep erythrocytes (SRBC)P OR E. coli LPS markedly influenced the immune response to these antigens. Simultaneous injection of the toxin with antigen resulted in a delayed appearance of antibody-forming cells during the first few days after immunization, followed by a marked enhancement of the peak numbers of antibody-forming cells. In the case of the immune response to SRBC, both 19S and 7S plaque-forming cells (PFC) were enhanced on the peak day of response after simulataneous immunization of toxin-injected mice. The secondary immune response to SRBC was also similarly affected when cholera toxin was given along with a second injection of erythrocytes: i.e. a delay in appearance of the first antibody-forming cells followed by a marked enhancement of the peak 19S and 7S PFC response. Injection of cholera toxin 103 days prior to SRBC or LPS was immunosuppressive. The effect of cholera toxin on the level of splenic cyclic AMP appeared related to the effects on antibody formation.