Inhibition by mouse serum of hemopoietic colony formation in vitro

The inhibitory activity of BALB/c serum for granulocytic and macrophage colony formation by mouse marrow cells in vitro was separable by flotation centrifugation into the very light density (VLD) fraction. On gel filtration the inhibitory material had an apparent molecular weight of 250,000 and on electrophoresis was localized as a single peak near the albumin region. These inhibitory preparations exhibited lack of specificity and inhibited colony formation by normal B-lymphocytes, lymphoid leukemic, plasma cytoma and mastocytoma cells. Preincubation of C57BL marrow cells at 37 degrees C with high concentrations of VLD fractions was cytotoxic and completely suppressed colony formation. Incubation at 0 degrees C or at 37 degrees C with low VLD concentrations caused a pattern of colony formation similar to that observed in cultures of marrow cells from mice with high serum inhibitory activity (CBA, BALC/c). The lack of specificity of serum inhibitors casts doubt on the role of these inhibitors as specific in vivo regulators of granulopoiesis and monocyte-macrophage formation.