Ea-A and Ea-E cellular antigen genes in Leghorn lines resistant and susceptible to acute cecal coccidiosis.

The purpose of the work was to explore the diversity and function of alloantigens in chickens differing in genetic resistance to acute cecal coccidiosis, Eimeria tenella (ACC). This paper describes A and E alloantigens, products of linked loci Ea-A and Ea-E, worked out in Leghorn lines R and S, previously selected for respective resistance and susceptibility to ACC. The R line possesses high frequency haplotypes A7E5 and A9E1 with very low frequencies of the recombinants. The S line possesses almost totally different haplotypes ranging from high to low frequency, respectively: A9E3, A9E5, A9E2, and A11E1. Alleles A7 and A11 were differentiated only by fortuitous production of an A reagent in other work on a commercial broiler line, suggesting that alloantigen variability in chickens is a continuum spanning varietal differences. The AE recombinants in both lines remained at very low frequencies for many generations after selection was suspended. Discussion is given for selection having been the most probable force producing nearly unique AE haplotypes in each of the two lines, largely from different cis-trans relations between similar A and E alleles. Thus, interactions of the A and E regions appeared to have been essential to the seeming action of AE on genetic resistance to ACC. The A and E antigens are shown to develop contemporaneously in ontogeny in the earliest generations of embryonic erythrocytes, further suggesting that AE is a coordinated functional complex.