Eosinophilia. I. Eosinophilia in guinea-pigs mediated by passive anaphylaxis and by antigen-antibody complexes containing homologous IgG1a and IgG1b.

There was an eight- to eleven-fold increase in the number of eosinophils in the peritoneal cavity of guinea-pigs repeatedly sensitized and subsequently challenged by that route. Peripheral blood eosinophilia was less and inconsistent. There were fewer eosinophils in the peritoneal cavity of guinea-pigs challenged intraperitoneally but sensitized by other routes, than in animals both sensitized and challenged peritoneally. Thus eosinophils were attracted to sites of antigenic challenge in anaphylactically sensitized tissue, particularly when sensitization occurred in the same tissue. In tissues repeatedly injected with antigen, there was an increase of mononuclear cells preceding and greater than the number of eosinophils. The relation between eosinophilia and anaphylaxis was substantiated by evoking eosinophilia in normal guinea-pigs challenged after passive sensitization with homologous IgG1a (conferring PCA sensitivity for 3 to 4 days), and with IgG1b (conferring PCA sensitivity for 7 to 9 days) which mediate anaphylaxis, but not in animals treated with IgG2, which does not. Similarly complexes containing IgG1 antibodies evoke eosinophilia in normal animals, but complexes containing IgG2 do not. Despite the association of eosinophilia with anaphylaxis, the number of peritoneal eosinophils following challenge is not greatly influenced by the susceptibility to fatal anaphylaxis, or by the serum PCA titre. Moreover it is doubtful whether passive sensitizing antibody mediates all the changes evoking eosinophilia on challenge, because guinea-pigs passively sensitized with IgG1 antibody for 16 hours had less eosinophilia on challenge than actively sensitized animals, though both passively and actively sensitized animals had the same titre of PCA antibody.