The ultrastructural localization of human neutrophil alkaline phosphatase in normal individuals during pregnancy and in patients with chronic granulocytic leukaemia.

The intracellular localization of alkaline phosphatase was determined in human neutrophils by electron microscope cytochemistry. In normal individuals, the largest and most intense deposits of reaction product was seen in a unique cytoplasmic granule population termed 'phosphasomes'. Lighter deposits were seen on nuclear membranes, some intracytoplasmic membranes lining vacuoles and granules and occasionally in focal patches on the internal surface of the plasma membrane. In cells isolated from women in the third trimester of pregnancy, activity was found in the same intracellular sites but there were, on average, more alkaline phosphatase-containing granules per cell than in the cells from non-pregnant individuals. Neutrophils from pregnant women were also characterized by the presence of large deposits of reaction product on the external surface of the plasma membrane (extramembranous). This activity had properties characteristic of the placental isoenzyme of alkaline phosphatase, found in serum during pregnancy. Neutrophils from patients with chronic granulocytic leukaemia, showing normal mature morphology, contained significant amounts of granule reaction product but there were fewer phosphasomes per cell than in normal individuals. In morphologically immature cells, reaction product was present in nuclear membranes, endoplasmic reticulum and large granules. These results were in agreement with previous biochemical data confirming a quantitative lack of alkaline phosphatase in chronic granulocytic leukaemia.