The bursa of Fabricius: a trapping site for environmental antigens.

The entry of environmental antigens into the lumen of the bursa of Fabricius was prevented by ligating the bursal duct prior to hatching (BDL: bursal duct ligation). The development of 'natural' serum agglutinins for bacteria and heteroerythrocytes was markedly suppressed by BDL. The antigen-specific recovery was observed by simultaneous administration of sterile antigens into the bursal lumen at the time of BDL. These results strongly suggest that the bursa of Fabricius is a major channel through which environmental antigens stimulate the immune system and induce the formation of 'natural' serum agglutinins.