A ROLE FOR BP-3 BST-1 ANTIGEN IN EARLY T-CELL DEVELOPMENT/

In the mouse thymus, pre-T cells are defined by their CD3(-)CD4(-)CD8( -) triple-negative, CD44(lo)CD25(+) phenotype. We made a rat mAb IF-7, that, among all T cell subsets analyzed, reacted exclusively with pre -T cells. Molecular cloning revealed that the antigen recognized by IF -7 was identical to BP-3/BST-1, a glycosyl-phosphatidylinositol-linked , CD38-related molecule previously described as a possible co-activati on molecule of pm-a cells. we found that IF-7 cross-linking enhances t he proliferative response of sorted pre-T cells to anti-CD3 stimulatio n. In addition, IF-7 enhances and accelerates the development of fetal thymic organ culture (FTOC), although the gamma delta lineage is unaf fected by the treatment. In addition, sorted IF-7(+) pre-T cells give preferentially rise to alpha beta TCR(+) thymocytes in FTOC. Our obser vations strongly suggest that BP-3/BST-1 is implicated in both early B and T cell growth and development, and is an early marker for the alp ha beta lineage.