Modulatory effects of fibronectin on in vitro lymphocyte responses.

In rat studies, fibronectin (Fn), a ubiquitous glycoprotein, is a T-cell mitogen and stimulates the production of interleukin 1 by peritoneal exudate macrophages. In contrast, Fn has no mitogenic activity for human lymphocytes and does not stimulate interleukin 1 release by human peripheral blood mononuclear cells. Fn increases in vitro peripheral blood mononuclear cell phytohemagglutinin responses in normals and patients with active, but not inactive, rheumatoid arthritis. Fn may alter local immunoregulation and play an active role in the rheumatoid synovial lesion.