Reversible binding of a guinea-pig lymphokine to gelatin and fibrinogen: possible relationship of macrophage agglutination factor and fibronectin.

Macrophage agglutination factor (MAggF) is a T-cell-dependent guinea-pig lymphokine with pH stability, heat stability and isoelectric point similar to fibronectin (see preceeding paper for details). Further observations confirm the similarity between MAggF and fibronectin. MAggF in unconcentrated lymph node cell culture supernatants bound reversibly to gelatin and fibrinogen. On gel filtration chromatography, most MAggF activity in a pooled concentrated lymphokine preparation was associated with molecules of 370,000 Daltons; lesser amounts of activity were found at 240,000 and 50,000 Daltons. All molecular weight forms of MAggF bound reversibly to gelatin. Guinea-pig plasma fibronectin prepared by affinity chromatography over gelatin had a molecular weight of about 450,000, a sub-unit on reduction of about 240,000 Daltons, and showed partial antigenic identity with human plasma fibronectin. Human and guinea-pig fibronectin preparations showed MAggF activity when tested using guinea-pig peritoneal macrophages, but their potencies relative to a culture supernatant standard did not correlate with the content of immunoprecipitable fibronectin measured by anti-human fibronectin antiserum. However, anti-human fibronectin immunoadsorbents specifically and reversibly bound MAggF activity in culture supernatants. On the basis of our observations, we suggest MAggF is a guinea-pig tissue fibronectin.