Induction of alkaline phosphatase activity in chronic myeloid leukemia cells: in vitro studies and speculative hypotheses.

Three patients with Ph chromosome + chronic myeloid leukemia (CML) in chronic phase suffered from intercurrent pleuritis of undefined origin. At that time, leucocyte alkaline phosphatase activity (LAPA) score was low for circulating neutrophils, but high for those from pleural effusion. LAP negative circulating CML granulocytes were incubated with the pleural liquid: after 40-70 hr, almost all were intensely LAP positive. This finding suggests that the low LAPA score in resting CML neutrophils is attributable to the absence of appropriate stimuli rather than to an incapacity to synthesize the enzyme.