Rapid adsorption of a foetal calf serum component by mammalian cells in culture. A potential source of artifacts in studies of antisera to cell-specific antigens.

Injection of CBA mice the either mitogen-stimulated (LPS or con A) CBA lymphocytes which had been cultured for 3 days in the presence of foetal calf serum (FCS) led to the production of antisera which reacted strongly with virtually all types of mammalian cells, including human, whether normal or malignant, provided they had been cultured in FCS-containing media. Reactivity was detected by sensitive immunological assays such as complement-dependent cytoxocity using rabbit complement (but not using guinea-pig complement), or EA-rosette inhibition of Fc receptor-bearing cells. The antisera did not react with fresh normal lymphoid cells or ascites tumour cells; however, these same cell populations became fully susceptible to the cytotoxic effects of the antisera after as little as 4 h incubation at 37 degrees in the presence of FCS. Cells incubated without FCS or with FCS at 0 degrees were not affected. The antisera reacted with FCS to form a single band on Ouchterlony double-diffusion plates. On immunoelectrophoresis the reactive antigen appeared to migrate in the alpha-globulin region of serum proteins. These observations suggest that FCS may be a source of potentially serious misinterpretations in immunological studies of cell-associated antigens using antisera produced by the injection of cells grown in FCS-containing cultures. Examples of artifcats arising from the use of FCS in certain systems, e.g. the preparation of alloantisera using cultured tumour cells vs fresh non-cultured lymphoid cells, are described.