The regulation system of granulopoiesis.

Extracts containing the granulocytic chalone (GCh) have been prepared from bone marrow conditioned medium by ultrafiltration and column chromatography. This preparation selectively inhibits myeloid cells and does not affect other, e.g., lymphoid cells. The action on myelopoiesis seems to include all mitotically competent immature granulocytes as indicated also by an inhibitory effect on bone marrow colony formation in agar. Results obtained by this technique and by applying mild trypsinization of bone marrow cells prior to testing chalone responsiveness indicate that GCh acts via membrane receptors. Finally the apparent antagonistic role of colony stimulating factor and GCh as regulators of granulopoiesis is discussed and a model of the regulation system is described.