B cells in epithelial and perivascular compartments of human adult thymus

The thymus is the site of T-cell differentiation. However, the relatively r ecent observation that B cells are also present in the human thymus has pro mpted studies to determine the origin and function of these B cells. Our st udies show that phenotypically distinguishable B cell populations are locat ed within both the thymic medulla and the thymic perivascular space and tha t cellular trafficking occurs between these compartments, including B cells trafficking from the periphery. The numbers of thymic B cells increase wit h age, correlating with increases in lymphocyte-rich regions of thymic peri vascular space that are prominent between ages 10 and 50 years. B cells wit hin. both thymic epithelial and perivascular compartments contain mutated i mmunoglobulin V-H sequences characteristic of post-germinal center B cells, suggesting that the B cells that most often give rise to thymic B-cell lym phomas may originate from either the thymic medulla or perivascular space. Copyright (C) 2001 by W.B. Saunders Company