CHARACTERIZATION OF IMMUNE-RESPONSE TO EIMERIA-TENELLA ANTIGENS IN A NATURAL IMMUNITY MODEL WITH HOSTS WHICH DIFFER SEROLOGICALLY AT THE B-LOCUS OF THE MAJOR HISTOCOMPATIBILITY COMPLEX

A model to simulate natural immunity to Eimeria tenella was developed in three chicken lines which differ at the B locus of the major histoc ompatibility complex, Homozygous, 1-day-old chicks of the (BB19)-B-19, (BB24)-B-24, or (BB30)-B-30 genotype were trickle immunized by being orally fed a small infectious dose of E. tenella oocysts for 5 consecu tive days, These naturally exposed birds were then challenged at diffe rent times between 5 and 24 days after the final dose, and the level o f protection was assessed 6 days after challenge, using body weight ga in and intestinal lesion scores, The duration of immunity in naturally exposed birds differed among the major histocompatibility complex lin es, Trickle immunization of the (BB19)-B-19 haplotype afforded the lon gest and strongest level of protection compared to the other two haplo types tested, In addition, in vitro splenic and peripheral blood lymph ocyte proliferative responses in trickle-immunized birds were measured against sporozoite, merozoite, and tissue culture-derived B. tenella parasite antigens isolated from the recently described SB-CEV-1/F7 est ablished cell line, The lymphocytes obtained from (BB19)-B-19 birds tr ickle immunized responded in vitro to the E. tenella-infected SB-CEV-1 /F7 tissue culture derived parasite antigen, Furthermore, antigen-spec ific immune responses appeared earlier in immune, challenged (BB19)-B- 19 birds than in their naive, challenged counterparts, The development of a model simulating natural immunization will serve as a foundation to further characterize both humoral and cell-mediated responses to E . tenella tissue culture-derived parasite antigens and to better under stand host protective immune responses to avian coccidiosis.