IMMUNOLOCALIZATION OF THE LACTOTRANSFERRIN RECEPTOR ON THE HUMAN T-LYMPHOBLASTIC CELL-LINE JURKAT

Monoclonal antibodies have been raised against the soluble lactotransf errin binding protein purified from the cell culture supernatant of Ju rkat cell line, a human T-lymphoblastic cell. Al monoclonal antibodies were able to specifically bind to the membrane of Jurkat cells. One o f the monoclonal antibodies, DP5B3G10, recognized both the soluble lac totransferrin-binding protein and the membrane lymphocyte lactotransfe rrin receptor after SDS-PAGE in presence of 2-mercaptoethanol and elec trotransfer on nitrocellulose. The monoclonal antibody DP5B3G10 inhibi ted the binding of lactotransferrin to Jurkat cells and human peripher al activated lymphocytes. In addition, lactotransferrin inhibited the binding of the monoclonal antibody to the cell surface. These results suggest that the 95 kDa lactotransferrin-binding protein isolated from the cell culture medium corresponds to the soluble form of the 105 kD a lymphocyte lactotransferrin receptor. Corresponding proteins of 105 kDa molecular mass were identified in Jurkat and CEM T-cells and Raji B-cells. Finally, the monoclonal antibody DP5B3G10 was used to immunol ocalize the lactotransferrin receptor on the Jurkat cells. Using fluor escence and electron microscopy, the receptor was localized both insid e and at the cell surface. The cell membrane receptor was associated i nto clusters. After permeabilization of the plasma membrane, the stain ing was positive in the peri-membrane area. The region near the nucleu s was devoid of receptor.