title: Epstein Barr virus binding induces internalization of the C3d receptor: a novel immunotoxin delivery system.
abstract: Epstein Barr virus (EBV) infection of human B lymphocytes is initiated by selective binding of the virus to the C3d receptor (EBV/C3d receptor) on the cell surface and results in polyclonal proliferation of infected cells. In these studies we examined the fate of the EBV/C3d receptor during viral infection by using an immunotoxin made from a monoclonal antibody (HB5) reactive with the receptor and the potent toxin, gelonin. Binding of the HB5-gelonin conjugate to the EBV/C3d receptor before EBV infection (at concentrations as low as 10(-11) M) significantly inhibited the subsequent polyclonal proliferation of virus-infected B lymphocytes. HB5 antibody and gelonin alone did not inhibit proliferation. Because internalization of gelonin-antibody conjugates is required to cause cytotoxicity, these results indicate that infection of B lymphocytes with EBV selectively induced endocytosis of the EBV/C3d receptor with concomitant internalization of the immunotoxin. Proliferation of B lymphocytes that were activated by prior infection with EBV, or activated by cross-linking of their surface immunoglobulin molecules, was not inhibited by the antibody-toxin conjugate even at concentrations as high as 10(-7) M. Also, the growth of B lymphoblastoid cell lines cultured in the presence or absence of infectious EBV was not inhibited by HB5-gelonin. Thus, our results suggest that the EBV/C3d receptor is internalized only during the infection of normal B lymphocytes by EBV, with co-internalization of immunotoxin, and indicate that internalization of the EBV/C3d receptor-immunotoxin complex does not occur simply as a consequence of activation and proliferation of B lymphocytes. The use of a ligand to induce endocytosis of its receptor offers a new strategy for the selective delivery of immunotoxins to cells and may be more generally applicable.
mesh_terms: D000328:Adult; D000911:Antibodies, Monoclonal / Q000633:toxicity*; D001402:B-Lymphocytes / Q000276:immunology; D001666:Binding Sites, Antibody; D002460:Cell Line; D002472:Cell Transformation, Viral; D003176:Complement C3 / Q000378:metabolism*; D006566:Herpesviridae Infections / Q000378:metabolism; D004854:Herpesvirus 4, Human / Q000378:metabolism*; D006801:Humans; D007166:Immunosuppressive Agents / Q000633:toxicity; D008213:Lymphocyte Activation; D010940:Plant Proteins / Q000378:metabolism / Q000633:toxicity; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism; D011951:Receptors, Complement / Q000378:metabolism*; D017464:Receptors, Complement 3d; D011991:Receptors, Virus / Q000378:metabolism; D054789:Ribosome Inactivating Proteins, Type 1
chemical_list: D000911:Antibodies, Monoclonal; D003176:Complement C3; D007166:Immunosuppressive Agents; D010940:Plant Proteins; D011947:Receptors, Antigen, B-Cell; D011951:Receptors, Complement; D017464:Receptors, Complement 3d; D011991:Receptors, Virus; D054789:Ribosome Inactivating Proteins, Type 1; C025674:GEL protein, Gelonium multiflorum