Experimental studies on cholera immunization. II. Evidence for protective antitoxic immunity mediated by serum antibodies as well as local antibodies.

By use of the ileal loop technique, the resistance to challenge with cholera enterotoxin was compared between unimmunized rabbits and rabbits immunized with toxin or toxoids. It was shown that subcutaneous as well as intraintestinal immunization induced protective immunity, the toxin being a better immunogen than Formalin-induced toxoid and much better than heat-induced toxoid. The relation between protection and serum antitoxin titer was poor, e.g., protection was seen in the absence of demonstrable serum antibodies. However, intravenous administration of antitoxic antiserum conferred some protection, suggesting that local as well as serum-mediated antitoxic immunity is operating in the host defence against cholera.