The immunological synapse and CD28-CD80 interactions

According to the two-signal model of T cell activation, costimulatory molec ules augment T cell receptor (TCR) signaling, whereas adhesion molecules en hance TCR-MHC-peptide recognition. The structure and binding properties of CD28 imply that it may perform both functions, blurring the distinction bet ween adhesion and costimulatory molecules. Our results show that CD28 on na ive T cells does not support adhesion and has little or no capacity for dir ectly enhancing TCR-MHC-peptide interactions. Instead of being dependent on costimulatory signaling, we propose that a key function of the immunologic al synapse is to generate a cellular microenvironment that favors the inter actions of potent secondary signaling molecules, such as CD28.