AUGMENTATION OF MATURE CD4(-CELL RESPONSES TO ISOLATED ANTIGENIC CLASS-II PROTEINS BY FIBRONECTIN AND INTERCELLULAR-ADHESION MOLECULE-1() T)

Mature CD4(+) T cells can undergo stable adhesion to isolated antigeni c MHC complexes, and upon TCR engagement exhibit up-regulated adhesion to the integrin ligands fibronectin (FN) and intercellular adhesion m olecule-1 (ICAM-1), Here, we have examined T cell responses to purifie d antigenic class II complexes, alone or coimmobilized in the presence of FN or ICAM-1, T cell adhesion to immobilized peptide-MHC complexes alone stimulated suboptimal, but marked levels of IFN-gamma and IL-2 secretion, and this was accompanied by cell proliferation, T cell adhe sion to both FN and ICAM-1 strongly augmented cytokine release and T c ell proliferation, Activation of V beta 3(+) and V beta 8(+) T cell li nes by isolated staphylococcal enterotoxin-MHC complexes was also exam ined, and surprisingly, a V beta 8(+) T cell line displayed significan t cell adhesion or later response to staphylococcal enterotoxin B-MHC complexes only when Ag was coimmobilized with ICAM-1 or FN, The result s demonstrate that adhesion of CD4(+) T cells to ICAM-1 or FN activate d by natural TCR ligands can strongly augment T cell signaling and dow nstream responses, Moreover, for some Ags, T cell interaction with acc essory ligands may be critical in attaining a threshold level of recep tor occupancy for cell activation.