The appearance of compound cilia in the nasal mucosa of normal human subjects following acute, in vivo exposure to sulfur dioxide.

Electron microscopic examination of ultrathin sections of ciliated nasal epithelium obtained from seven normal, healthy human volunteers indicated increases in the prevalence of compound cilia following controlled, acute exposure to 0.75 ppm sulfur dioxide (SO2). Morphometric analyses of the specimens confirmed a statistically significant association between SO2 exposure and compounding of nasal epithelial cilia in four of the seven subjects. Concomitant freeze-fracture replicas prepared from these samples also revealed the occurrence of compound cilia with accompanying evidence of abnormal ciliary membrane ultrastructure in the nasal epithelium. These studies indicate that SO2 may be implicated as a causative agent in ciliary compounding in the upper respiratory tract and that compound cilia represent a form of acquired ciliary defect which may serve as a readily quantifiable marker of epithelial injury.