Normal and neoplastic B cell development in the bursa of fabricius.

Abstract

The bursa of Fabricius plays a central role in the development of B lymphocytes in avian species (Grossi 1976; Lydyard 1976; Ratcliffe 1985). The bursal anlage becomes populated with lymphoid stem cells between 8 to 14 days of embryogenesis. These cells begin to express histocompatibility class II antigens (Ia) from day 10 (Ewert 1984) and surface immunoglobulin (slgM) from day 12 of embryonic life (Grossi 1976). By the time of hatching at day 21 of embryogenesi s, nearly all (>95%) of bursal lymphocytes express the phenotype of a mature B cell (sIa+, sIgM+). After hatching, the bursa continues to increase in size as the number of cells in an individual follicle increases and B cells begin to seed to other organs. The bursa reaches its maximum size between 8 to 12 weeks of age and then begins to involute. By 6 months of age all that is left is a sclerotic remnant of the bursa. Several lines of evidence suggest that the bursa plays a central role in the development of B cells. Birds bursectomized at 17 days of embryogenesis fail to develop B cells and become completely agammaglobulinemic (Cooper 1969), suggesting that normally B cell differentiation occurs exclusively in the bursa. If, however, one ablates the bursal epithelium at 60 hours of incubation, the resulting chickens lack a bursa but do develop some circulating B cells and serum Ig (Jalkanen 1983).