The role of secretory immunity in hepatitis A virus infection

Because the role of intestinal immunity remains uncertain in hepatitis A, samples of feces and saliva from infected primates and humans were tested for virus neutralizing activity. Only two of eight owl monkeys infected by the intragastric route developed neutralizing antibody detectable in extracts of feces collected up to 88 days after viral challenge, although serum neutralizing antibody was present in all monkeys by day 33. Similarly, neutralizing antibody was detected in fecal extracts from none of three experimentally infected human volunteers and only 1 of 15 naturally infected humans. The single positive human specimen contained occult blood. Only 2 of 19 saliva samples from naturally infected humans had significant viral neutralizing activity. In contrast, neutralizing antibody to type 2 poliovirus was present in most human fecal or saliva specimens tested. These data suggest that intestinal immunity does not play a significant role in protection against hepatitis A.