The Leucocyte Alkaline Phosphatase Activity in Mature Neutrophils of Different Ages

Abstract

The marrow myeloid precursor cells of a hematologically normal patient were labeled by i.v. injection of tritiated thymidine. Young labeled segmented neutrophils were then released from the marrow into the blood by an injection of cortisol. These PMN [polymorphonuclear leukocytes] had a significantly lower LAP [leukocyte alkaline phosphatase] activity than the older blood neutrophils. Within the morphologic boundaries of the segmented PMN, the cells are still in different stages of cytoplasmic maturation. In addition, labeled and unlabeled neutrophils showed a linear and parallel increase of LAP activity during the 24 h following cortisol injection. The neutrophil prematurely released in the blood can apparently mature into normal LAP-PMN. Generally, LAP activity of a blood neutrophil increases with time.