Cutting edge: TCR signaling induces selective exclusion of CD43 from the Tcell-antigen-presenting cell contact site

CD43, a large highly glycosylated molecule, is arguably the most abundant m olecule on the surface of T cells. Nevertheless, the function of CD43 remai ns unclear. Utilizing fluorescence microscopy, we find that CD43 is exclude d from the T cell-APC contact site. This exclusion is Ag dependent since op timal CD43 exclusion requires Ag-pulsed APC, and since signaling through CD 3, in the absence of any other receptor ligand interactions, can induce the modulation of CD43, These data suggest that CD43 may function as a barrier to nonspecific T cell-APC interactions that is removed as a result of T ce ll activation. Exclusion from the interaction site is a unique feature of C D43 and not universally found for all large highly glycosylated molecules s ince CD45 is not excluded. Thus, CD43 may represent a novel regulatory mole cule on the T cell surface that can direct T cell interactions by changing its location on the cell surface.