A low molecular weight factor in lung-conditioned medium stimulating granulocyte and monocyte colony formation in vitro

Medium conditioned by excised whole lungs from endotoxin-injected C₅₇BL mice was highly active in stimulating hemopoietic colony formation, particularly of granulocytic type, in agar cultures of mouse bone marrow cells. The colony stimulating factor (CSF) in this material had an α₁-α₂ electrophoretic mobility, was eluted from calcium phosphate gel by 0.04 M phosphate buffer and had an unusually low apparent S₂₀W of 1.9. Sequestered polymor-phonuclear neutrophils were excluded as a major source of this CSF. The high specific activity and ease of preparation of lung conditioned medium make it valuable both for the large scale production of CSF and as a source of an unusual type of CSF.