LOCALIZATION OF EOSINOPHIL-DERIVED NEUROTOXIN AND EOSINOPHIL CATIONICPROTEIN IN NEUTROPHILIC LEUKOCYTES

Eosinophil-derived neurotoxin (EDN) and eosinophil cationic protein (E CP) are generally regarded as eosinophil-specific proteins. We tested whether EDN and ECP are present iu mature neutrophils, By indirect imm unofluorescence, both eosinophils and neutrophils stained with antibod ies to EDN and ECP. Lq-sates of purified (<0.1% eosinophil contaminati on) neutrophils contained EDN, 112 +/- 4 ng/10(6) cells, and ECP, 163 +/- 2 ng/10(6) cells, whereas eosinophil major basic protein (MBP) was not detectable. Electron microscopic examination of immunogold-labele d buffy coat cells stained with EDN antibody showed that EDN is locali zed to neutrophil granules. Finally, EDN mRNA was detected in lysates of highly purified neutrophils (0.001% eosinophil contamination) by th e reverse transcription-polymerase chain reaction, We conclude that pr oteins that are either identical to or immunologically crossreactive w ith EDN and ECP are present in neutrophils and that EDN is synthesized and localized to neutrophil granules. Thus, caution must be exercised in interpreting the presence of EDN and ECP as specific markers of eo sinophil-associated inflammation in human disease.