Specificity of fixation loci for homocytotropic antibodies.

The heat-stable, homocytotropic antibody synthesized by guinea pigs to highly purified dextran has been studied by passive cutaneous anaphylaxis (PCA). Antibody arising in single guinea pigs was found to give PCA in some homologous recipients but not in others. Data are presented which indicate that the antibodies are bound in the skin of some animals to a greater degree than in that of others. This suggests some type of variability, perhaps allotypic, in the Fc portion of these immunoglobulins which relates to specificities of the loci where Fc becomes fixed in skin.