Leucocyte alkaline phosphatase as a marker of cell maturity: a quantitative cytochemical and autoradiographic study.

A sensitive and reproducible cytochemical technique for the demonstration of leucocyte alkaline phosphatase (LAP) has been evaluated. It produces a stable reaction product which can be readily quantified microphotometrically. In the circulating neutrophil polymorphonuclear leucocytes of rats the mean LAP levels measured in this way fluctuated only slightly from day to day. A highly significant correlation was demonstrated between LAP levels of neutrophils and their age, determined by isotope labelling with tritiated thymidine and by nuclear morphology. The correlation between the age of neutrophils and the complexity of their nuclear morphology has also been confirmed. The technique provides a useful tool for the study of leucocyte kinetics in disease states.