CD81 EXPRESSED ON HUMAN THYMOCYTES MEDIATES INTEGRIN ACTIVATION AND INTERLEUKIN 2-DEPENDENT PROLIFERATION

Lymphocyte recognition of antigen by the antigen-specific T cell recep tor (TCR) and coreceptor complexes rapidly alters the cell's adhesive properties facilitating high avidity cell-ligand interactions necessar y for lymphocyte development and function. Here, we report the express ion of CD81 (target of antiproliferative antigen [TAPA]-1) on human th ymocytes and the physical association of CD81 with CD4 and CD8 T cell coreceptors. Antibody ligation of CD81 on thymocytes promotes the rapi d induction of integrin-mediated cell-cell adhesion via lymphocyte fun ction-associated molecule-1 (LFA-1). Cross-linking CD81 is also shown to be costimulatory with signaling through the TCR/CD3 complex inducin g interleukin 2-dependent thymocyte proliferation. These data suggest that a CD81-mediated pathway in thymocytes is involved in the regulati on of both cell adhesion and activation.