Immunological and pharmacological analysis of the primary and secondary reagin response to Nippostrongylus brasiliensis in the rat

When systemic anaphylaxis has been induced in rats infected once with the nematode, Nippostrongylus brasiliensis, the gross pathological lesions are found in the small intestine (`early' anaphylaxis). When systemic anaphylaxis is induced in rats infected four times, these lesions appear predominantly in the lungs (`late' anaphylaxis). The reasons for the change in localization of the lesions have been studied.

Reaginic antibodies are involved in both `early' and `late' anaphylaxis but there was no difference in the physicochemical and biological properties of circulating reagins taken after one or after four infections. In particular, no differences in their preference for a distinct tissue structure was detected because, in rats given either `early' or `late' reaginic antibody, passive systemic anaphylaxis resulted in lesions restricted to the small intestine. The amount of `blocking' antibody increased after several successive infections and did not explain the decrease in sensitivity to systemic anaphylaxis which occurred in rats infected twice or three times.

Differences in the degree of anaphylactic sensitization of a given tissue were assessed by measuring titres of local reaginic antibody and concentrations of tissue histamine. Following an initial infection, anaphylactic sensitization is highest along the small intestine; following several successive infections, anaphylactic sensitization is especially high in lung tissue. It is suggested that the changes in the local site and degree of anaphylactic sensitization are due to the increase in immunity of the host which allows the parasite to migrate to the lungs but not to reach the intestine.