TNF-ALPHA BINDS TO THE N-TERMINAL DOMAIN OF FIBRONECTIN AND AUGMENTS THE BETA(1)-INTEGRIN-MEDIATED ADHESION OF CD4-LYMPHOCYTES TO THE GLYCOPROTEIN( T)

Certain inflammatory cytokines and growth factors have been previously shown to interact with glycosaminoglycan moieties of the extracellula r matrix (ECM). We have examined the association of the pleiotropic cy tokine TNF-alpha with glycoprotein constituents of ECM. TNF-alpha inte racted with fibronectin (FN) and laminin, and to a lesser degree with collagen. The major binding site for TNF-alpha on FN was localized to its 30-kDa N-terminal fragment (FN-N') with a K(i) in the sub-nM range . The binding of I-125-labeled TNF-alpha to immobilized FN or FN-N' pe rsisted for at least 24 h, and was specifically inhibited by antibodie s to FN, mAb directed against the FN-N' domain, unlabeled TNF-alpha, a nd by the truncated forms of TNF-alpha receptors. Once bound to immobi lized FN or FN-N', the cytokine could not be released by the soluble T NF-alpha-receptors, although it could be released by anti-TNF-alpha Ab . TNF-alpha was also found to interact with soluble FN, although with a lower affinity. Similar to the soluble cytokine, the FN-bound TNF-al pha appears to be functional; it augmented the beta1-integrin-mediated adhesiveness of activated CD4+ human T cells to the glycoprotein. Hen ce, binding of TNF-alpha to immobilized FN, which modifies its functio nal accessibility to soluble TNF-alpha receptors, does not abolish but rather may locally restrict its activity. This study suggests that a major ECM glycoprotein can present, in a restricted manner, a function al adhesion-modulating cytokine to immune cells, and that ECM glycopro teins may regulate their intrinsic cell-adhesive properties by associa ting with cytokines.