A double sandwich enzyme immunoassay using a combination of two polyclonal and one monoclonal antibodies was developed to quantitate transferrin in various human cell lines (U 937, K 562, Jiyoye, Jurkat, Raji, THP-1, HeLa) and transferrin secreted by these cells cultured in a defined protein-free medium. In the developed assay the measurable range in our experimental system is 1 to 25 ng/mL of human transferrin and the interassay coefficient of variation ranged from 11.3 to 16.1%. The assay is specific for both transferrin and apotransferrin with the same sensitivity. Intracellular transferrin levels in all the cell lines tested were < 1 ng/10(6) cells. The highest level of transferrin was found in cells of the histiocytic line U 937 (0.84 +/- 0.18 ng/10(6) cells). Only this cell line secreted transferrin in amounts > 1 ng/10(6) cells per day, i.e. 15.8 +/- 2.3 ng/10(6) cells per day. Intracellular transferrin was also demonstrated by immunoblotting.

Institute of Molecular Genetics Academy of Sciences of Czech Republic Prague

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