In vitro modulation of alkaline phosphatase activity in neutrophils from patients with chronic myelogenous leukemia by monocyte-derived activity.

To clarify the underlying mechanism of low neutrophil alkaline phosphatase (NAP) activity in chronic myelogenous leukemia (CML), CML neutrophils were cultured in liquid medium with different numbers of monocytes. Alkaline phosphatase activity in CML neutrophils, assessed cytochemically, increased with the numbers of monocytes. NAP activity was not induced by the interaction between neutrophils and monocytes, but by the presence of a monocyte-derived soluble activity. NAP activity in normal neutrophils was also lowered by depletion of monocytes from culture medium. Under such monocyte-depleted conditions, both CML and normal neutrophils proliferated and differentiated to produce mature neutrophils. Thus induction of NAP activity can be modified in vitro by changing the amount of NAP-inducing activity released from monocytes. However, whether a reduction of NAP-inducing activity in CML neutrophil is the cause of low NAP activity in vivo remains uncertain.