Localization of eosinophil-derived neurotoxin and eosinophil cationic protein in neutrophilic leukocytes.

Eosinophil-derived neurotoxin (EDN) and eosinophil cationic protein (ECP) are generally regarded as eosinophil-specific proteins. We tested whether EDN and ECP are present in mature neutrophils. By indirect immunofluorescence, both eosinophils and neutrophils stained with antibodies to EDN and ECP. Lysates of purified (F0.1% eosinophil contamination) neutrophils contained EDN, 112 6 4 ng/10 6 cells, and ECP, 163 6 2 ng/10 6 cells, whereas eosinophil major basic pro- tein (MBP) was not detectable. Electron micro- scopic examination of immunogold-labeled buffy coat cells stained with EDN antibody showed that EDN is localized to neutrophil granules. Finally, EDN mRNA was detected in lysates of highly purified neutrophils (0.001% eosinophil contami- nation) by the reverse transcription-polymerase chain reaction. We conclude that proteins that are either identical to or immunologically cross- reactive with EDN and ECP are present in neutro- phils and that EDN is synthesized and localized to neutrophil granules. Thus, caution must be exer- cised in interpreting the presence of EDN and ECP as specific markers of eosinophil-associated inflam- mation in human disease. J. Leukoc. Biol. 63: 715-722; 1998.