Properties of mouse homocytotropic and heterocytotropic antibodies

Mouse antisera were analyzed for the presence of homocytotropic and heterocytotropic antibodies. Two distinct populations of antibodies were detected by the homologous passive cutaneous anaphylaxis (PCA) reaction. The first was active 2 hr after injection, heat-stable, and partially reactive with antisera to mouse IgG1. The second was active 48 hr after injection, was heat-labile, and probably belonged to the IgE class of mouse immunoglobulins. In addition, it was demonstrated that there were also two antibodies active in the heterologous PCA reaction in rats, a heat-stable antibody and a heat=labile antibody. Contrary to results obtained with homocytotropic antibodies, none of the heterocytotropic antibodies detected reacted with antisera to mouse IgG1 or IgG2. These studies suggest that in addition to IgE there may exist another heterocytotropic antibody in mouse antisera and that caution should be employed when using the 2-hr PCA reaction in the rat as a sole criterion for detection of mouse IgE.