DIFFERENTIAL EXPRESSION OF ADHESION MOLECULES WITHIN THE HUMAN THYMUS

Development of a diverse, MHC-restricted yet self-tolerant T-cell repe rtoire occurs within the thymus, and requires contact between developi ng T cells and their stromal microenvironment. Such interactions are l ikely to depend on the combinatorial effect of specific adhesion molec ules. As a preliminary step to determining their role in T-cell develo pment, we have studied the distribution of LFA-1/ICAM-1, CD2/LFA-3, VL A-4/VCAM-1, and HECA 452-antigen/E-Selectin ligand pairs on frozen sec tions of human thymus. Using two color-immunohistochemistry, and a var iety of cell-lineage markers that reveal the nature of the cells on wh ich these adhesion molecules are located, we find a differential distr ibution of adhesion molecules, with some being shared by both endothel ial and epithelial cells. We also identify the VCAM-1-positive subpopu lation as cortical macrophages. The relevance of these findings to thy mopoiesis is discussed.