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Use of A Novel Fibronectin Receptor for Liver Infiltration by a Mouse Lymphoma Cell Line RL-1

Department of Pathology, Yamagata University School of Medicine, Yamagata 990-9585, Japan

The mechanism whereby some lymphomas invade liver extensively has not been fully investigated. There is no basement membrane under the sinusoidal endothelium of the liver, and hepatocytes produce fibronectin (FN); therefore, adhesion to this FN may be particularly important for liver infiltration by lymphoma cells. A mouse lymphoma cell line, RL-1, adhered to FN. However, this cell line did not express classical FN receptors such as very late antigen (VLA)-4 and VLA-5, as estimated by immunofluorescent staining. We have generated monoclonal antibodies (mAbs) that inhibit adhesion of RL-1 cells to FN. Western blot and immunoprecipitation analyses showed that the new mAbs recognize a protein with an approximate molecular weight of 55,000 (p55). This antigenic protein was highly purified by immunoprecipitation and processed for microsequencing. From NH₂-terminal sequence results, the p55 antigen was not identical to known FN receptors. Radioisotope-labeled RL-1 cells, when injected i.v. into mice, rapidly infiltrated the liver (30–35% of injected cells), as measured by a gamma counter. Intravenous injection of the new mAbs partially (20%) blocked the infiltration of i.v.-injected lymphoma cells into the liver, whereas control rat IgG and an anti-CD11a mAb did not. These results demonstrate that the mouse lymphoma cell line RL-1 uses a novel FN receptor for liver infiltration.