| Twelve murine lymphoid cell lines were screened in vitro for their adhesion to fibronectin-coated surfaces. Adhesion of these cell lines was found to vary with their states of differentiation. In general, B cell lines adhered to fibronectin better than either pre-B or T cell lines.;In addition, MOPC 315 was found to adhere to heparin-bound fragments (HBFs) of fibronectin. Neither the arg-gly-asp-ser sequence (RGDS, the cell-binding site of fibronectin) nor heparan sulfate inhibited MOPC 315 adhesion to HBFs. These results indicate that this adhesion was not mediated by a RGDS sequence that might be present in the HBFs nor by cell surface heparan sulfate. Protein molecule(s) appeared to be responsible for this interaction, since cycloheximide and trypsin treatments inhibited MOPC 315 adhesion to HBF. The adhesion of four other B cell lines and a BHK fibroblast line to HBFs and the cell-binding fragment (CBF) also was studied. Some cell lines adhered better to HBFs, whereas others adhered better to CBF. These observations suggest the presence of a second cell-binding site on the fibronectin molecule that can mediate lymphocyte adhesion. Lymphoid cell lines appeared to interact with CBF or HBF of fibronectin differently, which might have a role in regulation of lymphocyte localization in vivo by the differential expression of cell surface adhesion receptors.;A myeloma line, MOPC 315, was used to further characterize the adhesion process. Trypsin and cycloheximide treatment inhibited MOPC 315 adhesion to fibronectin suggesting that surface protein molecule(s) were involved in this process. The fibronectin receptor was identified by immunoprecipitation using an anti-fibronectin receptor antibody. This antibody precipitated a protein (MW of 140 kd) from solubilized cell preparations of nine cell lines. The expression of this protein was differentiation dependent, appearing only in B cell lines. |
