Persistence of primary antibody formation caused by the absence of antigen of microbial origin in the germ-free chicken.

Germ-free chickens showed a prolonged formation of primary anti-BSA and anti-HGG precipitating antibody after peak concentrations had been reached. This was indicated by the half-value times of the antibody concentration which in the germ-free birds showed 60–80 per cent higher values than in conventional controls (Germ-free anti-BSA: 8.0 and 7.5 days; conventional: 4.0, 4.1 and 4.4 days). Treatment of germ-free BSA-stimulated chickens with HGG 7 days later reduced the half-value time of anti-BSA precipitins from 7.5±0.6 to 5.0±0.1 days, bringing it in the range found in comparable conventional birds (4.4±0.2). Anti-HGG precipitins in these animals again showed the characteristic difference in antibody half-value time between germ-free and conventional birds. Prolonged precipitin production in germ-free chickens appears related to the lack of antigenic competition that occurs in animals harbouring a viable microflora. Treatment of the BSA-stimulated germ-free chickens with HGG suppresses the otherwise prolonged antibody formation supposedly by competing for potential immunocompetent cells.