A BSTRA CT A method has been developed for measuring neutrophil cellularity in normal human bone marrow, in which the neutrophil-erythroid ratio was determined from marrow sections and marrow normoblasts were estimated by the erythron iron turnover. Neutrophil maturational categories, defined by morphologic criteria, were supported by autoradiographs of marrow flashed-labeled with 3H-thymidine. Correction for multiple counting error was empirically derived by counting serial sections through cells of each maturational category. The normal neutrophil-erythroid ratio in 13 normal human subjects was 1.5±0.07. The mean number of normoblasts in the same subjects was estimated to be 5.07+0.84 X 10' cells/kg. Total marrow neutrophils (X 10' cells/kg) were 7.70±+1.20, the postmitotic pool (metamyelocytes, bands, and segmented forms) was 5.59±0.90 and the mitotic pool (promyelocytes + myelocytes) was 2.11+0.36.Marrow neutrophil ("total") production has been determined from the number of neutrophils comprising the postmitotic marrow pool divided by their transit time. Transit time was derived from the appearance in circulating neutrophils of injected 3H-thymidine. The postmitotic pool comprised 5.59±0.90 X 10' neutrophils/ kg, and the transit time was 6.60±0.03 days. From these data marrow neutrophil production was calculated to be 0.85 X 10' cells/kg per day.Effective production, measured as the turnover of circulating neutrophils labeled with 3H-thymidine, was 0.87±0.13 X 10' cells/kg per day. This value correlated well with the calculation of marrow neutrophil production. A larger turnover of 1.62+0.46 X 10' cells/kg per day was obtained when diisopropylfluorophosphate-3P Dr. Dancey's present address is Division of Hematology, Montreal General Hospital, Montreal, Quebec, Canada.Dr. Deubelbeiss' present address is Division of Hematology, Inselspital, Bern, Switzerland.Received for publication 27 February 1975 and in revised form 24 May 1976. was used to label circulating neutrophils. Studies using isologous cells doubly labeled with 3H-thymidine and diisopropylfluorophosphate-UP demonstrated a lower recovery and shorter ti of the 'P label.
INTRODUCTIONThe rate of neutrophil production can be measured as the turnover of neutrophils in either marrow or blood. Blood neutrophil turnover as determined with ["P1di-isopropylfluorophosphate (DFP) 1 cells has gained general acceptance: Cartwright et al.(1) in a study of 109 subjects, reported a mean turnover of 1.63 x 109 cells/ kg per day, and a similar figure of 1.36 X 109/kg per day was reported by Galbraith et al. (2) who studied 18 subjects. Such studies have provided an estimate of blood neutrophil turnover in normal man. Attempts to measure marrow neutrophil production have been indirect in the absence of reliable measurements of marrow cellularity. In this paper we describe a method for determining the number of marrow neutrophils and report measurements of basal rates of total production (marrow turnover) and effective production (blood turnover) of neutrophils in man.