T cells can use either T cell receptor or CD28 receptors to absorb and internalize cell surface molecules derived from antigen-presenting cells

At the site of contact between T cells and antigen-presenting cells (APCs), T cell receptor (TCR)-peptide-major histocompatibility complex (MHC) inter action is intensified by interactions between other molecules, notably by C D28 and lymphocyte function-associated antigen 1 (LFA-1) on T cells interac ting with B7 (B7-1 and B7-2), and intracellular adhesion molecule I (ICAM-1 ), respectively, on APCs. Here, we show that during T cell-APC interaction, T cells rapidly absorb various molecules from APCs onto the cell membrane and then internalize these molecules. This process is dictated by at least two receptors on T cells, namely CD28 and TCR molecules. The biological sig nificance of T cell uptake of molecules from APCs is unclear. One possibili ty is that this process may allow activated T cells to move freely from one APC to another and eventually gain entry into the circulation.