T-lymphocyte differentiation and the extracellular matrix: identification of a thymocyte subset that attaches specifically to fibronectin.

A population of murine thymocytes adheres specifically to fibronectin but not to vitronectin, laminin, or collagen type I. The interaction of these thymocytes with fibronectin could be inhibited by the synthetic peptide Gly-Arg-Gly-Asp-Ser-Pro, which comprises the previously identified cell-attachment determinant of the molecule, suggesting that the cell attachment site on fibronectin is recognized by these cells. A similar peptide, in which the aspartate residue had been replaced with glutamate, had no effect on this adhesion. The fibronectin-adherent thymocytes were found to be cortisone-sensitive; to bind peanut agglutinin; to have a Thy-1.2+, Ia- surface phenotype; and to express H-2 antigen only weakly on their surface. In addition, approximately 80% of the fibronectin-adherent cells expressed L3T4 and 80% expressed Ly-1 on their surface, whereas greater than 95% were positive for Ly-2. The data suggest that these cells, which constitute 10% of all thymic lymphocytes, are cortical thymocytes. We propose that their adhesion to fibronectin may be important for their differentiation. The binding to fibronectin provides a means to selectively isolate these cells for study.