Neutrophil products that inhibit cell proliferation: relation to granulocytic 'chalone'

Abstract

Various investigators have proposed the existence of a 'chalone' or product of mature granulocytes which inhibits the replication of granulocytic progenitors in a tissue-specific, species-nonspecific regulatory system. We tested this system utilizing purified populations of human leukocytes and a variety of proliferating target cell populations. Granulocyte-conditioned medium potently inhibited3H-thymidine incorporation in normal mouse bone marrow, in mouse erythroid precursors from spleens of phenylhydrazine-treated animals, and in human leukemic myeloblasts. This effect occurred without demonstrable cytotoxicity. Human marrow was only slightly inhibited and mitogen-stimulated proliferating lymphocytes were unaffected. Granulocyte-conditioned medium was also inhibitory in colony-forming assays for erythroid precursors but not for granulocyte precursors. It also reduced the mitotic index of proliferating erythroid progenitors in mouse spleen. Inhibitory activity was separable into at least two components on the basis of stability during heating and ultrafiltration, and in susceptibility to digestion by proteolytic enzymes. On the basis of these observations, we concluded that human granulocytes contain potent inhibitors of growth and3H-thymidine uptake of some proliferating hematopoietic cells, but these are not true granulocyte 'chalones'.