Recombinant interferon-gamma inhibits cell invasion by Eimeria tenella

Treatment of primary chicken kidney (CK) cultures with supernatants from concanavalin A-treated Eimeria tenella-immune avian splenic T cells significantly inhibited the invasion of the cells by sporozoites of E. tenella. Biochemical evaluation of this T-cell factor is consistent with the idea that this anti-Eimeria activity in the avian lymphokines is due to interferon-gamma (IFN-gamma). We then studied the effect of recombinant bovine and human IFN-gamma on the invasion of sporozoites of E. tenella in cultures of bovine and human cell lines, respectively. The initial infection of either the Madin-Darby bovine kidney cell line (MDBK) or the human larynx epidermoid carcinoma cell line (HEp-2) by the obligate intracellular protozoan parasite E. tenella was inhibited following a 24-h pretreatment with recombinant bovine or human IFN-gamma, respectively. The IFN-gamma-mediated inhibition was dose-dependent for both cell lines. Incubation of sporozoites of E. tenella with IFN-gamma alone before infection had no detectable inhibitory effect on cell invasion of either cell line by the parasite. In addition, the establishment of the antiinfective cellular state by IFN-gamma required at least a 16- to 24-h preincubation for significant inhibitory effects. These results are suggestive of a direct effect of the IFN-gamma on the host cells and not on the parasite themselves. Taken together these studies provide evidence for a role for IFN-gamma as a nonspecific mediator of host protection against coccidiosis.