Abstract
It has been shown that nucleated cells from bone marrow of a number of species including humans can give rise in vitro to colonies of mature granulocytic and mononuclear cells in semisolid media (1–3). These colonies arise from either single hemopoietic stem cells or cells committed to granulocytic differentiation which undergo division and maturation to yield colonies of 1000 or more cells (1).
In order for the process of maturation and division to occur in vitro, a specific stimulus is required. This stimulus for mouse marrow cells can be extracted from animal (including human) serum and urine, embryonic extracts, and a number of other tissue sources (1). The urinary colony stimulating factor (CSF) has been purified and appears to be a glycoprotein of molecular weight of 35,000 (1). Although there is heterogeneity among the other described CSF, most appear to be similar biochemically to that described in human urine (1).
Although factors stimulating human marrow cells are essentially the same, the quantitative differences among sources of CSF are large. While human urinary CSF stimulates 100–200 colonies from mouse marrow cells, it will stimulate only 10–20 colonies from the same number of human marrow cells (1, 3). A much more potent stimulus for human bone marrow is feeder layers of peripheral white blood cells (WBC) from humans (3). CSF from peripheral WBC has not been extracted or isolated but appears to be a protein factor secreted by metabolically intact cells (4, 5).
The mechanism and means by which various CSF initiate and stimulate colony formation is unknown. It is clear that CSF does not act merely as a triggering substance, but is necessary for every cell division in the maturation pathway (1). The present studies were done to determine whether the action of CSF is a cell surface related phenomenon.
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