Aberrant expression of active leukotriene C-4 synthase in CD16(+) neutrophils from patients with chronic myeloid leukemia

Elevated leukotriene (LT)C-4 synthase activity was observed in peripheral b lood granulocyte suspensions from patients with chronic myeloid leukemia (C ML). Magnetic cell sorting (MACS) with CD16 monoclonal antibodies (mAbs), w hich were used to fractionate granulocytes from CML patients and healthy in dividuals, yielded highly purified suspensions of CD16(+) neutrophils, The purity of these cell fractions was Verified by extensive morphologic examin ation. Reverse transcriptase-polymerase chain reaction (RT-PCR) analyses, d emonstrating the absence of interleukin-4 messenger RNA (IL-4 mRNA), furthe r confirmed the negligible contamination of eosinophils in these fractions. Notably, purified CML CD16(+) neutrophils from all tested patients transfo rmed exogenous LTA(4) to LTC4. These cells also produced LTC4 after activat ion with ionophore A23187 or the chemotactic peptide fMet-Leu-Phe (N-formy[ methionyl-[eucyl-phenylalanine). Subcellular fractionation revealed that th e enzyme activity was exclusively distributed to the microsomal fraction. E xpression of LTC4 synthase mRNA in CML CD16(+) neutrophils was confirmed by RT-PCR. Furthermore, Western blot analyses consistently demonstrated expre ssion of LTC4 synthase at the protein level in CML CD16(+) neutrophils, whe reas expression of microsomal glutathione S-transferase 2 occurred occasion ally. Expectedly, LTC4 synthase activity or expression of the protein could not be demonstrated in CD16(+) neutrophil sus-pensions from any of the hea lthy individuals, Instead, these cells, as well as CML CD16(+) neutrophils, transformed LTA(4) to LTB4. The results indicate that aberrant expression of LTC4 synthase is a regular feature of morphologically mature CML CD16(+) neutrophils, This abnormality, possibly associated with malignant transfor mation, can lead to increased LTC4 synthesis in vivo, Such overproduction m ay be of pathophysiological relevance because LTC4 has been demonstrated to stimulate proliferation of human bone marrow-derived myeloid progenitor ce lls, (C) 2000 by The American Society of Hematology.