Immunity to Eimeria tenella in young fowls (Gallus domesticus).

Complete immunity to a challenge dose of 100,000 sporulated oocysts of was developed in fowls 14 days after they had received the last of three graded doses of oocysts of this species, whereas uninfected fowls of comparable age were fully susceptible. In fowls similarly immunized, no detectable first-generation schizogony developed from challenge doses of 10 million oocysts administered to each fowl 21 days after the last of the three graded doses had been administered. Precipitating antibodies were demonstrated in some but not all of these immune fowls by the agar-gel diffusion technique. Precipitin bands, developed as the result of infection, showed a reaction of identity with those induced by parenteral injection of schizont antigen and most of the bands appeared to be directed against protein antigens. Cross reactions were observed between antiserum and antigens prepared from the species of coccidia, from the fowl and the species from the rabbit. Electrophoretic analysis of serum from immune birds showed an albumin component and four globulin fractions (I-IV); antibody activity was confined to the fraction with the slowest mobility (IV). No significant differences were shown between the electrophoretic analyses at comparable ages of serum from the infected and control groups of fowls between 7 and 63 days of age. The components in both groups altered significantly with time, showing a general rise in protein concentrations. Infected fowls repeatedly showed numerous pyroninophilic cells in the gut mucosa and cells closely resembling globular leucocytes in the deep glands of the caeca.