Expression of alkaline phosphatase (ALP) on the surface membrane of neutrop
hils (mNAP) was studied by immunofluorescence using an anti-ALP monoclonal
antibody. Fluorescent intensity distribution of mNAP was analyzed using FAG
S (fluorescence-activated cell sorter). The mean fluorescent intensity (MFI
) of the mNAP in this assay was well correlated with the neutrophil ALP (NA
P) score demonstrated cytochemically (r = 0.832). mNAP levels in Various he
matological disorders were evaluated by % mNAP(+) cells and MFI. The levels
in aplastic anemia and polycythemia vera were significantly higher, and in
chronic myelocytic leukemia and paroxysmal nocturnal hemoglobinuria (PNH),
the revels were significantly lower compared with the levels in healthy vo
lunteers. Two-color immunofluorescence with anti-ALP and anti-CD16 showed t
hat the PNH clone was essentially negative for mNAP, whereas residual norma
l neutrophils (CD16(+)) had levels slightly higher than those in normal ind
ividuals. Highly reproducible results were obtained in the blood samples wh
ich were stored at 4 degrees C for at least 24 hr without any treatment pri
or to immunofluorescent staining. No degradation of fluorescent intensity w
as seen 4 days after staining and fixation. The mNAP assay is simple, witho
ut subjective evaluation for quantification, and is useful far differential
diagnosis of hematological disorders. (C) 1999 Wiley-Liss, Inc.