Two kinds of extracts of peripheral blood leukocytes induced erythroblast increase and maturation in uitro in rabbit marrow cells. One extract was a secretion or exudate into plasma from intact leukocytes; the other was the supernatant after homogenizing the cells in ethanol. The extracts were less active than the intact leukocytes. The response with the two extracts together was a little greater than with either alone, but less than additive.
Blood leukocytes incubated in vitro with rabbit-marrow cells induced a several-fold increase in basophilic erythroblasts and smaller increases in acidophils and reticulocytes. The main effect was nearly complete in one hour at 37". Erythropoietin augmented the leukocyte effect; anti-erythropoietin inhibited i t with or without erythropoietin. The erythroblast increase came entirely from the marrow cells; the precursor cell class has not been identified, except that division of pre-existing basophils appears to be excluded. Autologous and homologous leukocytes were about equally effective.A method is described of measuring on stained smears changes in relative concentrations of different classes of cells induced experimentally. A method of preparing highly concentrated peripheral blood leukocytes is described.
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