Sheep red blood cell and Brucella abortus antibody responses in chickens selected for multitrait immunocompetence

Chickens from replicated lines divergently selected for multitrait immunocompetence were tested for their antibody responses to sheep red blood cells and Brucella abortus antigen. All birds were injected with sheep red blood cells and B. abortus antigens at 4 and 9 wk of age, and blood samples were taken 6, 8, and 10 d postimmunization. Antibody titers were determined by using agglutination assays. For sheep red blood cell responses, the most marked difference was between the high and low lines postsecondary immunization. The high line titer was still rising at 10 d, whereas the low line had reached its peak at 8 d and was decreasing. This may be a result of the selection process in which the high line is selected for a high, persistent response to two T cell-dependent antigens at 3 wk postimmunization. For B. abortus responses, the only differences were between high and low lines postsecondary immunization. The high lines were always higher than the low lines, with differences getting smaller as time postimmunization increased. In summary, selection for multitrait immunocompetence resulted in changes in antibody response to unrelated antigens.