"Natural" antibodies to chicken MHC antigens are present in mice, rats, humans, alligators and allogeneic chickens.

In the absence of any deliberate immunization, mice, rats, humans and alligators all have detectable titers of antibody against chicken red blood cells (CRBC's). Remarkably, this antibody is directed predominantly against private or public determinants of MHC proteins on the CRBC's, and little or no antibody is directed against species-specific determinants on MHC or other proteins, including other polymorphic blood group antigens. In chickens, "natural" antibody can be detected against CRBC's from all chickens differing at the MHC locus, but "natural" antibodies against other polymorphic antigens are not detected. Using a rosette-forming cell (RFC) assay, we have also shown that a large percentage of mouse spleen cells will rosette with chicken erythrocytes, and that the majority of these RFC's also recognize polymorphic antigens.