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Evolution in the structure and distribution of 4F2‐antigen from the oncofetal to the adult phenotype of human fibroblasts

The monoclonal antibody (MAb) 4F2 defines an oncofetal antigen in human fibroblastic cells. Two‐dimensional electrophoretic analysis reveals that tumor cell lines from mesenchymal tissues co‐express two or more heavy‐chain molecular variants of the antigen whereas the light subunit (41 kDa) is not affected. Among normal cells, only embryonic and newborn fibroblasts (from donors up to 20 days after birth) clearly co‐express two distinct molecular forms of the heavy chain with MW of 85 and 75 kDa, respectively. Cells derived from 3‐month‐old donors express detectable amounts of the 85 kDA but only faint traces of the 75 kDa subunit, while fibroblastic cells derived from donors older than 3 months seem to express only the 85 kDa subunit. Immunofluorescence analysis performed on adherent living cells shows that, in the first months after birth, there is a gradual evolution from the oncofetal to the adult phenotype also in the cell distribution of the 4F2. This evolution is reflected by a progressive disappearance of the 4F2 antigen from the cell membrane becoming, in adult normal cells, inaccessible to anti‐4F2 MAb. The existence of different molecular forms and different membrane positions of the 4F2 antigen could facilitate surveillance of morphological and structural changes in the evolution of human fibroblastic cells during the developmental process and neoplastic transformation.