Alkaline phosphatase activity in human polymorphonuclear leukocytes

Alkaline phosphatase has been localized ultracytochemically in PMN of man with normal and elevated levels of this enzyme. Contrary to guinea-pig PMN, no activity appears to be present in the specific granules. Instead, the plasma membrane and the membrane of the endocytic vacuoles show a strong staining. However, the demonstration of this activity depends on the preparatory procedure employed for PMN isolation. The use of dextran and Ficoll-Hypaque in the isolation procedure induces a marked increase in alkaline phosphatase staining of the PMN plasma membrane. Strongly increased activity at this site has been found in PMN from cancer patients. In most of them, additional staining has been observed in atypical vesicles and sometimes in the Golgi apparatus. These findings are discussed in the light of some previously reported controversial biochemical and cytochemical data on the distribution of alkaline phosphatase in human PMN.