Identification of neutrophil alkaline phosphatase‐inducing factor in cystic fluid of a human squamous cell carcinoma as granulocyte colony‐stimulating factor

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Abstract
We have previously shown that a factor termed neutrophil alkaline phosphatase‐inducing factor (NAP‐IF) has the capacity to induce neutrophil alkaline phosphatase (NAP) in postmitotic granulocytes (PMGs). This factor has characteristics similar to those of granulocyte colony‐stimulating factor (G‐CSF), suggesting that the two factors assayed by different methods may be attributable to an identical macromolecule. In a preliminary experiment, we showed that purified natural G‐CSF (nG‐CSF) could induce NAP in vitro in the presence of 10% (v/v) fetal calf serum (FCS). In this study, purified human nG‐CSF and recombinant G‐CSF (rG‐CSF) induced NAP in granulocytes from both normal individuals and patients with chronic myelogenous leukemia in a dose‐dependent fashion in serum‐free and serum‐containing culture conditions. The induction of NAP by G‐CSF was detectable at 0.4 ng/ml and became maximal between 10 and 20 ng/ml. Anti‐G‐CSF serum incubated with either NAP‐IF or rG‐CSF inhibited induction of NAP. Morphological examinations revealed that granulocytes cultured with G‐CSF were more mature than those cultured without G‐CSF, indicating that G‐CSF promoted maturation of granulocytes in parallel with NAP induction. These results indicate that NAP‐IF in the cystic fluid of a human squamous cell carcinoma is identical to G‐CSF and that induction of NAP by G‐CSF is really a reflection of cell maturation promoted by G‐CSF.