The viability of mononuclear phagocytes in vitro is diminished by the interaction of cells with serum proteins bound to the culture substratum

The long-term viability of bone marrow-derived mononuclear phagocytes in vitro was inversely correlated with the capacity of the cells to attach to the culture substratum. Mononuclear phagocytes suspended in medium containing 10% fetal bovine serum and subcultured on substrata coated with a 0.1% solution of poly(2-hydroxyethyl methacrylate) formed a population of non-adherent or loosely attached cells that remained viable for a 7 day incubation period. In contrast, cells subcultured under otherwise identical conditions on substrata optimal for cell attachment exhibited a 40-fold decline in cell number during the same period of time. The survival of mononuclear phagocytes subcultured under conditions which promoted cell attachment was increased by reducing the concentration of serum in the medium. Thus, cells subcultured 7 days in the complete absence of serum exhibited only a two-fold decline in cell number. However, mononuclear phagocytes subcultured in the absence of serum exhibited a ten-fold decline in cell number when cultured on substrata coated with serum proteins. This decline was reversed by the addition of the mononuclear phagocyte-specific growth factor, colony stimulating factor-1 (CSF-1) to the medium. These results indicate that serum proteins bound to the culture substratum exert a significant influence on the viability of adherent mononuclear phagocytes in vitro and on the requirement of cells for CSF-1 in order to survive.