Neutralization of Poliovirus by IgA Corpoantibodies

Summary Extracts of stools from normal children and adults neutralized the infectivity of poliovirus. The virus neutralizing activity was associated with IgA, the predominant immunoglobulin detected in fecal extracts. Two adult volunteers demonstrated IgA virus neutralizing copro-antibodies following oral infection with live attenuated poliovirus vaccine. The appearance of the intestinal antibodies coincided with reduction in the fecal excretion of vaccine virus. The infectivity of the excreted virus was significantly increased following reactivation of neutralized virus by antibody dissociation at pH 2.2, indicating the in vivo role of IgA coproantibodies as neutralizing agents. As a result of the degradation of coproantibodies by intestinal enzymes, stool extracts also contained antibody fragments which, although capable of only weak virus neutralization, demonstrated significant levels of specific poliovirus-combining activities. Specific attachment of antibody fragments was demonstrated by the reduction of infectivity of virus-fragment mixtures following reaction with anti-human globulin sera. The recovery of polio antibody fragments suggested the presence of significantly greater levels of virus neutralizing coproantibodies at the site of local antibody development than that reflected by conventional virus neutralizing techniques.