TNF-alpha Binds to the N-terminal Domain of Fibronectin and Augments the Beta 1-integrin-mediated Adhesion of CD4+ T Lymphocytes to the Glycoprotein

Certain inflammatory cytokines and growth factors have been previously shown to interact with glycosaminoglycan moieties of the extracellular matrix (ECM). We have examined the association of the pleiotropic cytokine TNF-alpha with glycoprotein constituents of ECM. TNF-alpha interacted 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 Ki in the sub-nM range. The binding of 125I-labeled TNF-alpha to immobilized FN or FN-N' persisted for at least 24 h, and was specifically inhibited by antibodies to FN, mAb directed against the FN-N' domain, unlabeled TNF-alpha, and by the truncated forms of TNF-alpha receptors. Once bound to immobilized FN or FN-N', the cytokine could not be released by the soluble TNF-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-alpha appears to be functional; it augmented the beta 1-integrin-mediated adhesiveness of activated CD4+ human T cells to the glycoprotein. Hence, binding of TNF-alpha to immobilized FN, which modifies its functional 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 functional adhesion-modulating cytokine to immune cells, and that ECM glycoproteins may regulate their intrinsic cell-adhesive properties by associating with cytokines.