Adhesion molecules involved in the interactions between early T cells and mesenchymal bone marrow stromal cells

We previously reported that among the various thymic lymphocyte subpopulati ons, the immature T cells preferentially adhere to mesenchymal bone marrow stroma, In the present study we examined the interactions between phenotypi cally defined populations of early T cells and stromal cell lines, The imma ture T cells segregated into two subpopulations according to their adhesive capacity. Whereas the majority of the adherent CD4(-)CD8(-) T cells were d evoid of CD3/TCR alpha beta, most of the nonadherent CD4(-)CD8(-) T cells e xpressed this receptor complex. The adhesion of T cells to bone marrow stro ma almost entirely was accounted for by CD49d and CD90, whereas that of adh erent CD4(-)CD8 cells also was dependent on CD44, CD62L, and CD117 receptor . Blocking antibody combinations failed to reduce the adherence of these ea rly T cells to less than 50% that of the control, On the other hand, the ad hesion of unselected thymocytes to the stroma was reduced by 80%, using the same blocking antibodies. Therefore, the participation of additional molec ules in the adhesion of early T cells to mesenchymal stroma is implicated. Comparison between the interaction of T cells with bone marrow mesenchymal or with thymus-derived epithelial stroma indicated that T cells utilize a s elected set of adhesion molecules under each situation. Although CD49d and CD90 participated in both cases, CD11a, CD18, and CD2 receptors played a do minant role in the adhesion of T cells to thymic epithelium only, This stud y may point to a role of mesenchymal stroma in the regulation of early T-ce ll lymphopoiesis in the bone marrow. (C) 1999 International Society for Exp erimental Hematology. Published by Elsevier Science Inc.