Monoclonal antibodies (GB16, GB18, GB19, GB22) raised against human placental microvilli recognize the transferrin receptor.

GB16, GB18, GB19 and GB22 are mouse monoclonal antibodies produced against full-term human placental microvilli. These antibodies reacted predominantly with the apical surface of the syncytiotrophoblast from first-trimester and full-term placentae, and also reacted with several cell lines derived from non-haematopoietic tissues by immunofluorescence. The radioiodinated BeWo (choriocarcinoma) cell surface proteins were immunoprecipitated with these four antibodies and analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The results demonstrated that the immunoprecipitates migrated at 180 and 90 kilodaltons under non-reducing and reducing conditions, respectively. Using enzyme-linked immunosorbent assay, the antigens recognized by GB16, GB18, GB19, and GB22 were able to bind human transferrin. Immunoabsorption studies showed that these four antibodies bound to the same molecule as OKT9, an antibody to the transferrin receptor. Moreover, the reactivities of these antibodies with HL-60 (promyelocytic leukaemia) cells diminished following dimethyl sulphoxide-induced differentiation by flow cytometric analysis. These data indicate that these four antibodies recognize the transferrin receptor. By competition assay, GB18 bound to an epitope different from those recognized by GB16, GB19 and GB22. In addition, GB22 displayed significant growth inhibition against the activated lymphocytes and Daudi cells, but not against HL-60 or Jurkat cells. These data suggest that these four monoclonal anti-transferrin receptor antibodies will provide additional means to investigate the physiological roles played by the transferrin receptor.