CUTTING EDGE - STIMULATION OF CD28 WITH B7-2 PROMOTES FOCAL ADHESION-LIKE CELL CONTACTS WHERE RHO FAMILY SMALL G-PROTEINS ACCUMULATE IN T-CELLS

Unless a costimulatory signal is provided, TCR recognition of Ag bound to the MHC is insufficient to induce optimal T cell proliferation or the production of IL-2, Here we show that the stimulation of CD28, a T cell costimulatory receptor, by a specific Ab increases F-actin conte nts in T cells, The interaction between T cells and B7-2-transfected C hinese hamster ovary cells expressing the CD28 ligand leads to the rea rrangement of the actin cytoskelton in the region of cell-cell contact , Within the Rho family of G proteins, Rac1, but not Rho, translocates to the sites of cell-cell contact where Tailin also accumulates, Thes e results indicate that the interaction between B7-2 and CD28 establis hes a focal adhesion-like cell contact between T cell and APCs. The re sults also suggest that CD28 signaling is primarily transduced by a cy toskeletal rearrangment/signaling pathway mediated by the Rho family G proteins.