An assay, the paper radioallergosorbent test (PRAST), for the measurement of specific serum IgE antibody in the rat is described in detail. This assay has been used, in conjunction with a modified PRAST for the determination of relative specific serum IgG antibody and the PRIST assay for total serum IgE [13], to measure specific IgE and IgG and total IgE immune responses in normal parasite infected rats immunized using various protocols. The results indicate that there is a relationship between the basic IgE level and the immune response, i.e. a rat strain with a low constitutive IgE level demonstrates a weak response whereas a high level strain reacts strongly. When PRAST and passive cutaneous anaphylaxis (PCA) were compared, using standardized IgE antibody containing sera, the results were in good agreement. However, PRAST is the preferable assay as it shows less intrinsic variation, is more sensitive than PCA, and is not influenced by high serum IgE levels in the recipient animal.

A/SN mice infected with N. Brasiliensis showed depressed anti-DNP antibody responses following immunization with DNP-Asc in alum. The immunosuppression was only observed when infection preceded immunization by between 2 and 7 days, and was not achieved when the interval was extended to 10 days. The suppression lasted at least 50 days, and affected IgE levels more than IgG1 or IgG agglutinating anti-DNP antibodies. A high dose of infective larvae (500-1000 per mouse) was necessary to induce suppression. Use of low dose irradiation indicated a parasite-induced radiosensitive component of the mouse immune system which negatively regulated the anti-DNP IgE response. These results suggested that the parasite could induce suppression in an analogous manner to sequential antigen-induced suppression (AIS).