Investigations on Eosinophilia*.

SUMMARY.— Eosinophilia in guinea‐pigs and mice is mediated by antibodies that sensitize tissues anaphylactically. In the guinea‐pig these are guinea‐pig γ1 globulin antibodies and rabbit passive sensitizing antibodies; in the mouse, mouse γ1 globulin and reagin. The γ2 globulin antibodies in both species, mediate Arthus reactions without eosinophilia. However, in vitro, there is no difference between eosinophils and neutrophils in their response to antigen‐antibody complexes containing either γ2 or γ1 globulin, which are ingested by both types of cell. Eosinophils in anaphylactic or parasitized tissues are particularly attracted to large, basophilic mononuclear cells which are found in mesenteric milk spots, around parasitic granulomata and probably in lymph nodes. Histamine fails to evoke eosinophilia in guinea‐pigs and rats, though it traps eosinophils in the tissues, forming an apparent eosinophilia. Anti‐histamine drugs fail to suppress the eosinophilia of anaphylaxis in guinea‐pigs. Though generalized or local anaphylaxis results in eosinophilia, it is not known whether complexes of antigen with tissue passive sensitizing antibody on the cell surface attract the eosinophils, or whether they are attracted by some vascular permeability factor released from the anaphylactic cells.