Immune responses to infections with coccidia in chickens: gut hypersensitivity.

Sporulated oocysts or oocyst hulls of Eimeria acervulina given via the crop, and oocyst juice or sporozoites inoculated directly into the intestinal lumen, were tested for their effects on the hypersensitivity of the intestines of immunized and susceptible birds. Only viable sporozoites consistently caused an increase in the permeability of the immunized intestine to macromolecules, shown by the leakage of intravenously injected dye. Repulsion of epithelium and disruption of the villi were seen more often in immunized than in susceptible chickens but there was no correlation with treatment or with dye leakage. The hypersensitive response of immune intestines challenged with a heterologous organism was approximately half as intense as the response to homologous challenge. The significance of these findings in relation to immunity to coccidiosis is discussed.