Modulating action of Escherichia coli heat-stable enterotoxin (STa) on the humoral immune response

The effect of Escherichia coli enterotoxin STa on the primary and secondary immune response in F1 (CBA × C57 B1/10) mice immunized against sheep red blood cells (SRBC) was investigated. Modulating action on the IgM and IgG response was found to be dependent on the dose-time administration of the toxin. Immunosuppression of the primary response on the 4th day after immunization was observed when the toxin was injected 15 min before the SRBC, followed by immunostimulation on the 6th day after antigen (Ag) injection. Moreover, toxin administration 48 h before SRBC caused immunosuppression of the primary immune response on the 4th and 6th days. On the other hand, the IgM and IgG secondary immune response, determined 6 days after boosting, was greatly enhanced by toxin administration 15 min before priming (day 0) or boosting (day 26) and 48 h before priming. The same response was suppressed by toxin administration 48 h before booster antigen injection.