Abstract
A FACTOR is present in the serum and urine of mice and humans which can stimulate the formation of granulocytic and macrophage colonies by mouse bone marrow cells in agar culture1–3. Levels of this colony stimulating factor (CSF) can be assayed in bone marrow cultures because of the sigmoid relationship between CSF concentration and colony numbers3. Previous studies showed that serum CSF levels were elevated in mice with various types of leukaemia1,4. Although serum colony stimulating activity seemed to be high in some patients with leukaemia5, a direct comparison of CSF levels in normal and leukaemic human sera was prevented by an inability to detect CSF in normal human serum.
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