T cell fibronectin: an unexpected inflammatory lymphokine.

T cell fibronectin (FN) is a product of antigen and mitogen activated human, murine and guinea pig T lymphocytes. Operationally and functionally, T cell FN is a lymphokine associated with delayed hypersensitivity. T cell FN acts at femtomolar concentrations to agglutinate mononuclear phagocytes and translocate monocytes and neutrophils through model extracellular matrices, and is 1.1 x 10(4) to 2.3 x 10(6) times more potent than other FN for these activities. It does not act on peripheral blood lymphocytes. Macrophage agglutination mediated by T cell FN requires cellular metabolism and depends on interactions between multiple classes of cell surface protein receptors and FN gelatin- and cell-binding domains. In contrast, translocation of cells through artificial matrices mediated by T cell FN is a biophysical process dependent on interactions between surface heparan sulfates on responding cells and FN amino-terminal heparin-binding and gelatin-binding domains. The correlation between the ability of cloned murine T cell lines to produce FN and their ability to transfer delayed hypersensitivity reactions suggests that secretion of T cell FN may be an important element in the initiation of these responses. The double activity of T cell FN could allow it to enhance influx of phagocytic effector cells and retain monocytes at tissue sites of T cell activation.