Flow-cytometric analysis of leukocyte alkaline phosphatase in myelodysplastic syndromes

The expression of leukocyte alkaline phosphatase (LAP) in neutrophils is re duced in some patients with myelodysplastic syndrome (MDS), We quantitative ly assayed for LAP in MDS leukocytes by a flow cytometry based method using a monoclonal antibody raised against human bone alkaline phosphatase. The LAP expression was assayed in blood samples from a group of 46 MRS patients , consisting of 39 patients with refractory anemia (RA), 3 with RA with exc ess blasts (RAEB), and 4 patients with RAEB in transformation. The percenta ge of LAP-positive cells was significantly higher in the MDS patients than in the normal subjects and also higher in IRA than in RAEB and RAEB in tran sformation. To investigate the cause of the elevated LAP expression, we mea sured the serum concentrations of several cytokines. The granulocyte colony -stimulating factor (G-CSF) level was significantly elevated in MDS patient s, and the serum G-CSF concentration clearly correlated with the percentage of LAP-positive cells. Thus, the LAP activity in RA is higher than in norm al subjects, and G-CSF is thought to be one of the causes stimulating LAP e xpression in MDS neutrophils.