Immune response and disease resistance in chickens. I. Selection for high and low titer to Salmonella pullorum antigen.

A selection experiment for high and low anti-Salmonella pullorum antibody titer was carried out over four generations within the B1B1 blood group genotype in chickens. The study was aimed primarily at identifying different response patterns controlled by immune response genes linked to the B system, the major histocompatibility complex of the chicken. Maximal divergence was obtained in the third generation of selection when agglutination titers of 1/320 and 1/80 in B1B1 high and low responders, respectively, were reached. Immune response of S. pullorum was deduced to be controlled by polygenes. The B1B1 population, selected for high immune response to S. pullorum antigen, consistently had greater total mortality as well as greater susceptibility to challenge with Marek's disease virus compared with B1B1 population selected for low response. This, however, is believed to be a consequence of random drift of genes for disease resistance in the relatively small populations and not a direct consequence of selection for high or low S. pullorum titer.