Parasite exposure elicits a preferential T-cell response involved in protective immunity against Eimeria species in chickens primed by an internal-image anti-idiotypic antibody.

Polyclonal anti-idiotype 1073 (anti-Id 1073), raised against a monoclonal antibody specific for the protective epitope(s) of Eimeria tenella sporozoites, induced cell-mediated immune (CMI) responses in bursectomized chickens. Whereas alhydrogel-adsorbed anti-Id 1073 was sufficient to engender the CMI response at 4 h after injection, induction of the CMI response at 24 h required both alhydrogel and muramyl dipeptide sterol. Exposure of immunized chickens to live parasites prompted a dichotomous effect on the CMI response engendered by anti-Id in that the 4-h CMI response was preferentially stimulated and the 24-h CMI response was down regulated. Both types of CMI response were transferable to naive chickens by T cells from anti-Id 1073 immune donors or by parasite-specific T cells from clones 21 and 27. These T-cell clones were generated from chickens immunized by repeated infections with E. tenella and showed in vitro proliferative responses to anti-Id 1073. The abilities of T cells from clone 21 to selectively transfer the 4-h CMI response and to generate gamma interferon to activate macrophages for their cytotoxic effects on Eimeria sporozoites correlate with the preferential stimulation by parasites of the 4-h CMI response in chickens immunized with anti-Id 1073. These data show that anti-Id 1073 mimics the protective epitope(s) of the parasite and primes chickens for protective CMI responses. Cytotoxic T cells, equivalent to the mammalian T-cell subset of the Lyt2+ phenotype, appear to be the primary effector T cells in the CMI response engendered by anti-Id 1073 against Eimeria parasites.