CHICKEN B-CELLS UNDERGO DISCRETE DEVELOPMENTAL-CHANGES IN SURFACE CARBOHYDRATE STRUCTURE THAT APPEAR TO PLAY A ROLE IN DIRECTING LYMPHOCYTEMIGRATION DURING EMBRYOGENESIS

The migration of progenitor cells to specific microenvironments is ess ential for the development of complex organisms. Avian species possess a unique primary lymphoid organ, the bursa of Fabricius, that plays a central role in the development of B cells. B cell progenitors, howev er, arise outside the bursa of Fabricius and, during embryonic develop ment, must migrate through the vasculature to the bursa of Fabricius. In this report, we demonstrate that these progenitor B cells express t he sialyl Lewis x carbohydrate structure previously shown to be a liga nd for the selectin family of vascular adhesion receptors. Soon after migration to the bursa of Fabricius, B cell progenitors are induced to undergo a developmental switch and terminate the expression of sialyl Lewis x in a temporal pattern that correlates with the developmental decline in the ability of these cells to home to the bursa of Fabriciu s upon transplantation. The induction of the developmental switch in t he glycosylation pattern of developing B cells requires the bursal env ironment, In addition, sialyl Lewis x carbohydrate determinants or str ucturally similar determinants on the surface of immortalized bursal l ymphoid stem cells participate in the adherence of these cells to the vascular regions of the bursal microenvironment, These data demonstrat e that the carbohydrate structure sialyl Lewis x is developmentally re gulated during chicken B cell development and may facilitate the migra tion of B cell progenitors to the bursal microenvironment by serving a s a ligand for a lectin-like adhesion receptor.