Analysis of the expression of the 4F2 surface antigen in normal and neoplastic fibroblastic human cells of embryonic and adult origin.

4F2 monoclonal antibody recognizes a 120-kD glycoprotein on the surface of human spread fibroblastic cells of embryonic and neoplastic origin, but it does not bind to normal spread adult fibroblasts. Flow cytometric analysis reveals that human adult fibroblasts become 4F2-positive when they are analyzed as round-shaped cells; this means that, in normal adult cells, 4F2 antigen behaves as a cryptic molecule. Thus, the basic difference between embryonic, neoplastic and normal adult cells consists in a different organization in the architecture of the cell membrane, since in embryonic and neoplastic cells there is a continuous expression of the 4F2 antigen independently of the cell shape and cell cycle phase. Quantitative flow cytometry shows that the mean surface density (MSD) of the 4F2 antigen 1, does not vary as a function of the cell cycle; 2, is inversely related to cell size and "metabolic time". This suggests that at the plateau phase the surface organization of G1 resting cells changes as a function of the number of days spent in culture; and 3, sarcoma and SV40-transformed cells show significantly increased MSD levels of the 4F2 antigen in comparison with normal cells of similar size. Electrophoretic analysis under reducing conditions confirms the quantitative differences in the expression of the 4F2 antigen described with the cell sorter. It also reveals, in a way different from that previously found with lymphoid cells, the coexistence of two molecules (85 and 73 kD) in the heavy chain regions. The 73 kD is, however, much more strongly expressed in the fibrosarcoma than in the embryonic cells. Finally, it shows that 4F2 antigen is a very useful tool for studying the organization and the structure of the cell membrane of human fibroblasts and can provide new insights to understand better the developmental and transformation processes.