Effects of lactoferrin on human granulopoiesis in vitro.

It has been proposed that Lactoferrin plays a negative feedback role in regulating granulopoiesis through its ability to suppress Colony-Stimulating Factor production. However, an analysis of experimental data, based on cell kinetic principles, does not support this contention. The basic point is that the concentration of Colony-Stimulating Factor determines the rate of clonal amplification, and mean clonal size. The latter is a reliable index with which to quantify the level of stimulation in a system. With this index it was found that Lactoferrin: did not suppress the de novo production of colony factor by blood mononuclear leukocytes affected the rate of cell proliferation both in the absence and presence of preformed Colony-Stimulating Factor. It was also found that Lactoferrin influenced myelocyte progression through the cell cycle. These findings suggest that the action of Lactoferrin is more complex than was previously believed and its relevance as a regulator of granulopoiesis is unclear.