A study of the rat passive cutaneous anaphylaxis (PCA) reaction for the assay of mouse IgE antibody

The rat PCA reaction for assay of mouse IgE antibody was investigated. PCA reactivity was examined in rats with different characteristics in terms of strain, sex, age and rearing conditions. Sprague-Dawley (S-D), Fischer and Wistar strain rats were almost equally appropriate for the assay. The male rat was recommended in spite of the comparable PCA reactivity to the female since the male showed less non-specific bluing. PCA reactivity of the germ-free rat was comparable to that of the conventional animal. PCA reactivity appeared at 3 weeks of age, increased up to 11–13 weeks and remained constant until 40 weeks of age. PCA titers assayed in the rostral, caudal, lateral or central side of the back were comparable. The PCA reaction was poor when elicited with a 15 min sensitization period, became progressively stronger to reach a plateau at 4 h and remained constant until 72 h. Heating conditions required to demonstrate thermolability of IgE antibodies were studied. Incubation of undiluted antiserum at 56°C for 2 h abolished the reaginic activity. Reaginic activity of an antiserum diluted in saline was relatively resistant to heat, but diluted reaginic antibody was equally sensitive to heat in the presence of normal mouse serum (NMS) or HGG in the dileunt. NMS must be coexistent with reaginic antibody on heating to confer thermolability since preheated NMS used for dilution had no effect on the PCA titer of an antiserum.