Generation of a long-lived IgE response in high and low responder strains of rat by co-administration of ricin and antigen.

Certain strains of rats infested with the nematode parasite Nippostrongulus brasiliensis mount vigorous, persistent immunoglobulin E (IgE) responses. In the absence of parasites, adjuvants such as Bordatella pertussis or Al(OH)3 are needed to produce IgE responses to soluble antigens. These are short-lived, even in high IgE responder strains. In this study we have produced long-lived IgE responses in both low (Wistar) and high (Brown Norway) IgE responder strains of rats by repeated injections of ricin, a toxic lectin from castor beans, and phospholipase A2 (PLA2), a bee venom protein. Total IgE levels rose from 30 +/- 20 ng/ml to 39,000 +/- 7500 ng/ml in the Wistar rats compared with an increase from 120 +/- 100 ng/ml to 47,000 +/- 8000 ng/ml in the Brown Norway rats. An even greater (10(4)-fold) increase was seen in PLA2-specific IgE antibody levels. total and PLA2-specific IgE started to fall 6 weeks after treatment was stopped in the Wistar and after 12 weeks in the Brown Norway rats. The duration of the response was 204 and 248 days, respectively. The IgE-enhancing properties of ricin were compared in low, mid (Hooded Lister) and high IgE responder rats. Total IgE and PLA2-specific IgE but not IgG antibody (Ab) responses were enhanced in all animals given ricin and PLA2 but not in animals given ricin or PLA2 alone. The increase was greater in Wistar rats (48-fold) than in Brown Norway rats (eightfold) and by Day 24 the levels of both total and PLA2-specific IgE in three different strains were indistinguishable. PLA2-specific IgE antibody-secreting cells were detected in the spleen at a frequency of 1:5000. These results show: (i) that repeated immunization of rats with antigen and ricin produce a very large IgE response which was long-lived; (ii) that this response was indistinguishable in different IgE responder strains of rat; and (iii) that the IgE response declines earlier in low IgE responder strains of rats.