Characterization of cell-mediated responses to Eimeria acervulina antigens

In order to identify antigens from Eimeria acervulina eliciting cell-mediated as well as humoral immune responses, merozoite and sporozoite fractions were separated by electrophoresis and injected into chickens. Coccidia-specific antibody titers, lymphocyte proliferation, and interferon production were measured to determine whether the inoculations sensitized the chickens to merozoites and sporozoites. Several fractions from merozoites and sporozoites induced humoral or cell-mediated responses. Merozoite fraction 4 (molecular weight [MW] 12,700-18,400) had the most consistent high interferon production; it also had good antibody production after challenge but not before challenge. Merozoite fraction 3 (MW 18,400-29,000) elicited high antibody titers and modest proliferation. Merozoite fraction 2 (MW 29,000-43,000) elicited consistently high proliferation; however, antibody responses were normal and interferon production was lower than that in the control. Merozoite fraction 5 (MW 6000-12,700) results were modest for all three parameters. Sporozoite fractions 5 and 6 (MW 12,700-29,000) elicited good antibody titers after challenge. The only sporozoite fraction that showed any interferon induction, fraction 2 (MW 69,000-200,000), also elicited good proliferation, although it did not stimulate antibody production. Sporozoite fraction 1 (> 200,000 MW) had very high proliferation potential. These findings support the hypothesis that different antigens preferentially elicited different T-cell responses.