A LYMPHOSTROMAL MOLECULE, THYMIC SHARED AG-1, REGULATES EARLY THYMOCYTE DEVELOPMENT IN FETAL THYMUS ORGAN-CULTURE

Previously, we detailed the characterization of thymic shared Ag-1, a unique marker of immature thymocytes and isolated thymic stromal cells , defined by the mAb MTS 35. In this study, the functional relevance o f this molecule to thymopoiesis was investigated by the addition of pu rified MTS 35 to fetal thymus organ culture. It down-regulated thymic shared Ag-1 expression and dramatically reduced thymocyte cell yield t hrough inhibition of alphabeta-TcR+ T cell differentiation, post CD3-C D4-CD8- triple negative thymocytes. These effects were specific for th e mAb MTS 35, because controls, which include both isotype-matched and other lymphostromal mAb, showed no similar effects. These results dem onstrate that thymic shared Ag-1 is a functionally important marker of early thymocyte differentiation, particularly with regard to the alph abeta-TcR lineage.