Modulation of in vivo antibody responses by cholera toxin.

Treatment of mice with an exotoxin (0.01 mug to 1.0 mug) purified from Vibrio cholerae culture filtrates markedly influenced the immune response to sheep erythrocytes (SRBC) and the Escherichia coli lipopolysaccharide (LPS). Simultaneous administration of the toxin (CT) with antigen resulted in a delayed appearance of antibody plaque-forming cells (PFC) during the first few days after immunization, followed by a marked enhancement of both IgM and IgG PFC. The secondary immune response to SRBC was also similarly affected when CT was given together with a second inoculation of SRBC; i.e., a delay in appearance of hemolytic PFC followed by a markedly enhanced IgM and IgG PFC response. Treatment of mice with cholera toxin 1 to 3 days before SRBC or LPS was immunosuppressive. The effect of CT on the level of splenic cyclic AMP appeared related to the effects on antibody formation.