Abstract
The agar culture method for growing colonies of granulocytes and macrophages from bone marrow cells has provided a technique for assaying a humoral factor, the colony-stimulating factor (CSF), which is found in plasma (1) and urine (2). This factor appears to be similar to CSF produced by feeder layers of bone marrow (3), peripheral leukocytes (4) or kidney cells (5). In general, colonies of bone marrow do not form unless this stimulant is continually present. Shad-duck and Nunna (1) found elevation of CSF in serum only during experimentally induced neutropenia, favoring the view that CSF is a humoral regulator of myelopoiesis.
Although serum does not usually stimulate bone marrow colonies, Bradley, Metcalf and Robinson (6) found CSF in serum of AKR mice when leukemia developed. Bradley and Siemienowicz (7) also reported stimulation of rat bone marrow by normal rat serum. In both cases, however, fetal bovine serum was used in the culture. The question of whether normal serum can stimulate bone marrow without interaction with some other factor has not been resolved.
We have developed a liquid tissue culture system for the study of bone marrow stimulants. In this system proliferation begins by the second day and reaches a peak on the third or fourth day (unpublished data) which is equal to or greater than that of the original specimen. Macrophage transformation is prominent by day two and is complete by day seven. We have found that conditioned media or heterologous sera are not required for marrow growth. However, conditioned medium can be shown to have a synergistic effect with serum when serum is limiting.
Materials and Methods. One milliliter of bone marrow aspirate from an unanesthetized calf 1-8 wk old was dispersed in 200 ml of cold Eagle's minimal essential medium (MEM) without anticoagulant and collected by centrifugation.
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