Identification of an anti-human osteogenic sarcoma monoclonal-antibody-defined antigen on mitogen-stimulated peripheral blood mononuclear cells.

An anti-human osteogenic sarcoma monoclonal antibody (mouse IgG2b) termed 791T/36 was found to exert complement-dependent cytotoxicity against phytohaemagglutinin (PHA)-stimulated peripheral blood mononuclear (PBMN) cells. This reaction was examined by flow cytofluorimetry using indirect membrane immunofluorescence to detect cell-bound antibody and by measurement of the binding of fluorescein-isothiocyanate-conjugated 791T/36 antibody to cells. The antibody reacted strongly with peripheral blood blast cells induced by PHA, and there was negligible reactivity with resting lymphocytes. Maximum binding was observed after 3 days' culture with PHA, coinciding with maximum DNA synthesis, and this represented of the order of 2 X 10(5) antibody molecules bound per cell. After cell surface radioiodination of PHA-stimulated PBMN cells, detergent lysis and immunoprecipitation of antigen with 791T/36 antibody and Sepharose-protein A, the apparent molecular weight of this antigen was determined to be 72,000 by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. This is identical to that of the 791T/36-defined antigen expressed on various osteogenic sarcoma cell lines [3, 17], and by this criterion the antigen is distinguishable from other cell surface markers of activated human lymphocytes.