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An assay, the paper radioimmunosorbent test (PRIST) for the measurement of total serum IgE in the rat, that allows the measurement of IgE down to a level of 0.25 ng/ml, is described. With this assay it has been demonstrated that significant differences exist in normal serum IgE levels in non-immunized rats. These differences are strain-dependent, and strains may be classified as to low (less than 50 ng/ml), medium (50--300 ng/ml) or high (greater than 300 ng/ml) serum levels. The serum IgE level is not sex-dependent. Environmental factors have a pronounced influence, optimal housing conditions resulting in low and stable levels while suboptimal conditions result in high levels with great fluctuations. Hybridization experiments suggest a multigenic control, with low IgE strains having a dominating suppressor effect.

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.