Antibody-mediated inhibition of immune responsiveness in baby chicks

An experimental model for the analysis of antibody-mediated regulation of specific immune responsiveness in chickens is described. Chick embryos and day-old chicks were passively administered homologous serum with high anti-mouse erythrocyte (MRBC) activity and then tested for immune responsiveness to MRBC several weeks later. Compared to the untreated controls, the hemagglutinin titers of experimental birds were obviously depressed for 2 to 3 weeks but near normal by the 4th week. The inhibitory property of homologous serum appeared directly related to the anit-MRBC activity; serum samples collected on day 1 and 2 after immunization were ineffective and low in specific activity, whereas those collected after the 3rd day were progressively more inhibitory as the anti-MRBC activity increased.