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Non-heat-inactivated fetal calf serum contains a factor, FCS-MIF, that inhibits in vitro the migration of guinea pig peritoneal macrophages. FCS-MIF is partially or completely inactivated by dialysis, repeated freezing and thawing, heating to 56°C for 30 min, and changes of pH beyond the range of 6.0 to 7.7. Chromatography in different gels and with different buffers suggests that several fractions may have MIF activity. FCS also contains a factor, FCS-MSF, that stimulates the migration of guinea pig macrophages. It is detected after MIF is removed by chromatography on DEAE-Sephadex A-25. A stimulatory factor is also present in supernatants of sensitized guinea pig lymphoid cells stimulated with antigen and is detected when the supernatants are treated in the same fashion as FCS to uncover FCS-MSF.
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Fox et al. (1974) studied this question.
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