Induction of adjuvant-independent IgE responses in inbred mice: primary, secondary, and persistent IgE responses to ovalbumin and ovomucoid.

Immunization of a number of inbred mouse strains intraperitoneally with low levels (1-100 micrograms) of ovalbumin (OA) or ovomucoid (OM) in the absence of adjuvant, revealed marked strain differences in IgE responsiveness. High-OA-responder strains such as Balb/c exhibited PCA titre up to 256 in the primary response, and up to 1,280 in the secondary, while non-responders such as SJL and NZB remained PCA negative; similar variations were found in the response of the strains to OM. Repeated immunization of high-OA-responder mice with low doses of antigen without adjuvant elicited anamnestic second and tertiary HA antibody responses. In contrast, IgE responses exhibited anamnestic secondary responses, but were not further boosted by tertiary stimulation. Instead, a 'persistent' high IgE response of the type previously associated with the use of specialized adjuvants, developed in these mice. Fractionation of the OA antigen by gel filtration yielded molecular species (dimers pentamers) of considerably greater IgE-immunogenicity than either monomeric OA or very highly aggregated forms. Immunization of high-OA-responder mice with the former permitted lowering of the threshold for induction of adjuvant-independent primary OA-IgE responses to a single 1.0 microgram dose, and the threshold for priming to 0.1 microgram.