Normal range of blood colony-forming cells (CFU-C) in humans: influence of experimental conditions, age, sex, and diurnal variations.

Blood colony-forming cells (CFU-C) and colony-stimulating activity obtained from feeder layers of peripheral blood leucocytes (leucocyte CSA) have been studies in 69 normal subjects by means of semisolid agar culture system. Groups of normal volunteers were selected according to sex and age (20 to 45 and older than 60 years) and the results compared. The mean number of circulating CFU-C was significantly lower in young women (20-45 years old) than in males over 60 years of age, but no differences were found among the other age and sex groups. Leucocyte CSA did not significantly differ among these groups. In 5 young males the blood CFU-C did not show significant variations at 8 AM and at 4 PM of the same day. When the study was repeated in 18 subjects at longer time intervals, the number of colonies showed a maximum fivefold variation. The amount of plasma and polymorphonuclear granulocytes present in our culture system did not inhibit the colony growth. In most cases, double layer cultures grow a higher number of colonies than single layer, but feeder layers of some normal subject seem to inhibit the colony growth.