Characterization of lymphokine fibronectin from guinea pig lymphoid cell culture supernatants

Fibronectins (FN) in guinea pig lymphoid cell culture supernatants have been studied using a panel of polyclonal and monoclonal anti-FN antibodies to clarify their relationship with macrophage agglutination factor (MAggF), an inflammatory lymphokine sharing many properties with this family of high molecular weight glycoproteins. MAggF contained cellular FN epitopes, and was reversibly bound by antibodies specific for cellular FN. Enzyme-linked immunoassay and inhibition of MAggF activity by monoclonal anti-plasma FN antibodies revealed immunoreactive FN in guinea pig lymphoid cell culture supernatants to share three epitopes with plasma FN and to lack a fourth epitope present in plasma FN. Immunoreactive FN in gelatin-affinity purified lymph node cell culture supernatants was polydisperse; MAggF activity (Mr 410 kD) was associated with only 13% of total immunoreactive FN. Although a low molecular weight FN fragment (Mr 67 kD) was associated with MAggF activity in salt-fractionated peritoneal exudate culture supernatants, it was not possible to generate MAggF activity by limited proteolysis of MAggF-inactive, high molecular weight FN in lymph node cell culture supernatants. We conclude that MAggF is a cellular FN containing a number of epitopes in common with plasma FN and suggest it may be a unique species of cellular FN produced by T lymphocytes involved in initiating delayed hypersensitivity reactions.