TNF-α production by eosinophils in upper airways inflammation (nasal polyposis)

TNF-α is a cytokine with a wide spectrum of proinflammatory activities. Nasal polyps (NP), which occur in association with allergic rhinitis and asthma, are characterized by a marked infiltration of activated eosinophils, epithelial damage, and varying degrees of stromal fibrosis. By using Southern blot analysis after a reverse transcription-PCR, we detected a signal specific for TNF-α mRNA in five of seven NP samples, but not in control nasal mucosal samples. With in situ hybridization, we detected cells expressing mRNA specific for TNF-α in eight of thirteen NP samples, but not in four control samples. Counterstaining with chromotrope 2R demonstrated that virtually all cells expressing TNF-α message were eosinophils. The ratio of eosinophils expressing TNF-α to the total number of eosinophils varied greatly among tissues; as an average, we observed 24% TNF-α-positive eosinophils. Using a mAb against human TNF-α, we demonstrated TNF-α localization in 12 NP tissues (48.8 ± 16.5 positive cells/mm²) but not in three control samples. Morphologically, cells localizing TNF-α were both mononucleated and polynucleated with only a small number of eosinophils, as determined by aniline blue counter-staining. Studies of purified blood eosinophils from a patient with hypereosinophilic syndrome and from four healthy donors indicated that TNF-α is produced, but rapidly secreted, so that TNF-α mRNA-positive cells contain little detectable protein. Furthermore, cells that retain detectable TNF-α may not contain sufficient TNF-α mRNA to be detected by using the probe developed for our studies. Together, these findings identify a novel mechanism by which eosinophils may contribute to mucosal inflammation and provide an approach to future investigation.