Effects of Exogenous Proteins Injection into the Bursa of Fabricius on Humoral Immunity in Neonatal Chickens

Early researches have shown that the bursa of Fabricius is a critical organ for development of B lymphocytes in birds. Exogenous proteins from the gut lumen or the environment are taken up by the follicle-associated epithelium and enter into the bursal follicle. Not all of the B lymphocytes in the bursal follicle mature and emigrate to the periphery and antigen-dependent selection for B lymphocytes may occur in the bursa. However, the actual impact of antigens in the bursa on B cells is not clear. In this study, dinitrophenyl (DNP) or 2,4,6-trinitrophenyl (TNP) coupled bovine serum albumin (BSA) was injected into the bursa of one-day-old chickens, a time when most B lymphocytes in the bursal follicles begun to emigrate from the medulla to the cortex. Immunohistochemical analysis showed that DNP-BSA was only distributed in the bursal medulla. By injecting TNP-BSA into the bursa of one-day-old chickens, and immunizing the chickens with TNP-HSA 3 weeks later, we found that injection of TNP-BSA increased anti-TNP titers in the sera of chickens after immunization. Taken together, the results suggest that the bursa is the site of B cell-antigen interaction and is capable of causing Ag-specific B cell emigration and increasing an antigen-specific immune response at the B cell level.