Characterization of resistance and immunity to Eimeria tenella among major histocompatibility complex B-F/B-G recombinant hosts.

The relative influence of the B-F vs. B-G chromosomal regions on innate resistance and immunity to Eimeria tenella was studied among six B-F/B-G recombinants, designated BR1, BR3, BR4, BR5, BR6, and BR8. In one experiment, resistance was studied among 340 F1 chicks each carrying the B17 allele derived from Line UCD.003 and therefore also heterozygous for one of the B recombinant haplotypes. In a second experiment, acquired immunity was studied among 161 F2 chicks each carrying one B17 allele and segregating for one of the recombinant alleles. In Experiment 1, F1 chicks of similar haplotypes, BR3 and BR4 (BF2-G23), gained significantly more weight than those with BR1 (BF24-G23) and BR5 (BF21-G19) following exposure to a single high dose of 25,000 oocysts, although no differences in lesion scores were detected among the six recombinants. Following exposure to a single low dose of 2,500 oocysts, F1 chicks BR3 and BR4 also gained significantly more weight and had significantly lower lesion scores than BR1 or BR5 F1 chicks. To study acquired immunity in the F2 homozygous chicks, five consecutive daily exposures of 500 oocysts were followed 21 days later by challenge with 10,000 oocysts. The BR5 (BF21-G19) and BR6 (BF21-G23) homozygous chicks, both carrying the B-F21 allele, showed significant protection in terms of reduced lesion scores. These results demonstrate that E. tenella parasitism manifests itself to varying degrees in chicken hosts possessing different recombinant major histocompatibility complex haplotypes.