Genetic control of immunity to Eimeria tenella. Interaction of MHC genes and non-MHC linked genes influences levels of disease susceptibility in chickens.

The relative importance of MHC genes and background genes in the genetic control of disease susceptibility and the development of protective immunity to E. tenella infection was investigated in eight different strains of 15I5-B congenic and four inbred chicken strains. RPRL 15I5-B congenic chickens that share a common genetic background but express different B haplotypes demonstrated wide variations in disease susceptibility and the development of acquired resistance to E. tenella infection. Infection of chickens sharing a common B haplotype but expressing different genetic backgrounds showed quite contrasting levels of susceptibility to secondary E. tenella infection. In all chicken strains examined, infected chickens developed high levels of serum and biliary anti-coccidial antibodies regardless of their B haplotypes. Furthermore, no correlation between antibody levels and the phenotypically expressed levels of disease resistance was demonstrated. These findings lend support to the view that interaction of MHC genes and non-MHC genes influences the outcome of host response to E. tenella infection.