Reagin-like antibodies in rats infected with the nematode parasite Nippostrongylus brasiliensis.

The immune response to in rats is closely associated with the formation of antibodies resembling human reagins. These are detected in some rats immediately after acquiring resistance to the parasite after an initial infection and in all rats 1 week later. Further infections stimulate an anamnestic rise in reagin' production. Reagin' formation is due to the living worms, primarily the adult stage. Reagins' were detected by passive cutaneous anaphylaxis in the rat (homologous passive cutaneous anaphylaxis=PCA) with a 72-hour interval between intradermal injection of antibody and intravenous injection of antigen, which was a saline extract of adult worms. Reagin' production in rats vaccinated with worm extracts contrasts sharply with reagin' production in rats infected with living worms. Vaccination with worm extracts stimulates reagin' production in only some rats during the primary response only; after second and later vaccinations, reagins' were not detected in any rats. Prolonged vaccination induces the formation of blocking' antibodies and a further type of antibody capable of inducing 6-hour PCA, but not 72-hour PCA in rats. Even after prolonged vaccination, however, a subsequent infection stimulates an anamnestic rise in reagin' production in some rats. Vaccination did not induce resistance to infection in any rats. Rats recovered from an initial infection become increasingly susceptible to anaphylactic shock when challenged with worm antigen, but the sensitivity of rats to systemic anaphylaxis is not closely correlated to the level of circulating reagins'. Heterologous anaphylactic reactions did not induce expulsion of worms from the intestine and anaphylaxis is not directly related to the ability of rats to resist infection.