IgE in Paragonimus ohirai-Infected Rats: Relationship between Titer, Migration Route, and Parasite Age

In rats infected with Paragonimus ohirai (P.o.), IgE response against the parasite was influenced by both the site of metacercarial inoculation and the age of the inoculated worms, whereas the IHA response was not influenced by these variables. Intraperitoneal infection and oral infection with 10 metacercariae induced a high level of P.o.-specific IgE (maximum PCA titer of 1:128 and 1:111, respectively). In contrast, intrapleural infection induced little IgE (1:496, maximum titer). Thus migration of the parasite in the peritoneal cavity and the liver, or the former alone, was an important event in the production of IgE, because intrapleurally inoculated metacercariae normally develop into mature worms without migrating into the abdominal cavity. Intraperitoneal transplantation of five immature or adult worms produced significantly lower IgE levels and correlated with the age of the transplanted worms. Four-week-old worms were observed to induce negligible or no P.o.-specific, IgE antibody. The stage-specific, IgE resonse observed in infections established by transplantation appears to be partly dependent on migration of the parasite in the abdominal cavity. Worms in the pleural cavity may have suppressed IgE production.