NI Project Title: 16, Molecular and Cellular Radiobiology Effects of Radiation and Chemicals on Control of Hemopoiesis RX-03-02-(b) Technical Progress in FY 1973: (Cone'd.) Bone marrow and peripheral blood cells combined with EP-producing cells from glomerular cultures are now cultured to see if the intimate mixture of EPproducing cells with the HSC will initiate active erythropoiesis. Studies relevant to granulopoiesis confirmed thac a humoral factor diffuses from the irradiated host into diffusion chambers stimulating growth of granulocytic cells, CFUs, and macrophages. Intermittent hypoxia during the culture period reduces the yield of granulocytic cells and macrophages which suggests competition forthe HSC common for erythrocytes, granulocytes, and macrophages. Study of the growth of the HSC was extended to the culture of normal concentrates of human peripheral blood in the diffusion chamber. Significant growth was observed only in irradiated mice. ,* Unidentified and largely lymphocytoid blast cells increased exponentially during the first eleven days in culture; during the first 2-3 days the number of small Lymphocytes decreased and then remained constant. This raises the question as to whether the decrease in the small lymphocyte population is the result of transformation and proliferation into the large lymphocytoid blast cell. Granulocytes decrease rapidly during the first 5-6 days in culture, approaching zero levels. At 8-9 days, proliferating eosinophils and neutrophils appear, followed within 24-48 hours by an increase in numbers of non-dividing eosinophils and neutrophils, In older cultures there is a striking increase in the number of plasmacytoid cells which appear at a time when the large blast cells are diminishing in number, suggesting a relationship between the two. The time parameters of cell proliferation in the diffusion chambers, after labeling with tritiated thymidine, were shown to be a little faster than those observed in earlier in vivo studies, The measurement of the DNA content of myelocytes (in collaboration with Killmann and Ernst, University of Copenhagen), showed that approximately 62% of myelocytes have a 2n DNA contenc, indicating that they are either in the G, phase or have gone out of cycle on their way to becoming metamyelocytes. This fulfills the first requirement of the BNL model for granulocytopoiesis. Studies were initiated on the quescion of whether myelocyte cycle time is shortened at the expense of the G, period by inflammation, thus allowing time for another mitosis with an increased output of neutrophils. ~in dogs show: Preliminary 1) in the normal steady state small myelocytes R like 2n DNA cells (not labeled by tritiated thymidine); 2) the "flash" tg index is increased by inflammation; 3) myelocytes progress through the céll cycle and replace metamyelocytes more rapidly. 17. Expected Results in FY 1974: Fe-55 suicide studies will continue with emphasis on study of the apparent intramedullary feedback loop between the differentiated erythropoietic compartment and the HSC responsible for accelerating the flow of (See Continuation Sheet) b119290 RX - 230