The Effect of Neutropenia on the Cell Cycle of Granulocyte Precursors in an In Vivo Culture System

Proliferation of myeloid elements, macrophages, and pluripotent stem cells (CFU) in diffusion chamber cultures of normal mouse bone marrow was examined. The relative growth of differentiated cells and CFU was clearly inhibited when the concentration of cells cultured was increased from 10⁵ to 20 x 10⁵ per chamber. When chambers were implanted into neutropenic hosts the growth of CFU and granulocytic cells was enhanced. The generative cycle of the earliest recognizable granulocytic cells, as estimated by flash labeling with tritiated thymidine, was comparable to that seen in normal bone marrow and was significantly shortened by culture in a neutropenic environment. Growth of pluripotent stem cells and myeloid elements in these cultures appears to be influenced both by short-range factors related to cell concentration and by long-range humoral factors.