Cellular Characteristics of the Eosinophil Compatible with a Dual Role in Host Defense in Parasitic Infections *

Peripheral blood and tissue hypereosinophilia are characteristics of diverse invasive parasitic infestations in animals and humans. As the initial development of peripheral blood eosinophilia after exposure to the parasites exhibits a latent period which is markedly reduced upon the subsequent reintroduction of parasites, an immunological reaction to parasite antigens has been considered a prerequisite for peripheral blood eosinophilia. Both humoral and cellular immunological reactions have been implicated in the peripheral blood hypereosinophilia of parasitic infestations. The oral administration of Taenia taeniaeformis eggs to rats leads to eosinophilia which reaches a peak level 3 wk after a primary infection and a heightened eosinophilia 3 to 7 days after a secondary challenge. The passive transfer of anti-T. taeniaeformis antisera, or fractions rich in antibodies of the IgG2a or IgE class, followed by the oral administration of eggs produces a peripheral blood eosinophilia exhibiting comparable features to those of challenged naturally immune rats.