Numerous theories have been presented that attempt to explain the frequent recurrences of pharyngotonsillitis caused by Streptococcus pyogenes; these recurrences occur after seemingly adequate antibiotic treatment. We previously have demonstrated that Spyogenes can survive for up to 7 days intracellularly in immortalized human respiratory epithelial cells grown in an antibiotic supplemented medium. Viable S pyogenes were externalized and established an extracellular infection, whenever the extracellular antibiotic was removed. We have investigated the presence of intracellular S pyogenes in two in vivo studies using respiratory epithelial cells collected from patients with tonsillitis and the tonsils of asymptomatic carriers. Electron microscopy and immunohistochemistry demonstrated intracellular S pyogenes in pharyngeal epithelial cells in 13 of 14 patients with tonsillitis (93%). Furthermore, intracellular S pyogenes were found in macrophage-like cells in eight (73%) and in epithelial cells in four (36%) tonsils from 11 asymptomatic S pyogenes carriers. These in vivo data strongly support the hypothesis that intracellular S pyogenes can constitute a reservoir of bacteria with the potential to cause reinfections.

The purpose of this study was to investigate the occurrence of free radicals, nitric oxide (NO), superoxide (O^–₂) and peroxynitrite, in the inner ear of the guinea pig following intratympanic injection with 5 mg of gentamicin (GM). Forty-eight hours after GM injection, varying degrees of degeneration of the inner ear were observed. Immunohistochemical study revealed immunoreactivity to NO synthase II (which generates NO) and to xanthine oxidase (which generates O^–₂) in both the vestibular organ and the organ of Corti. Immunohistochemical investigation, using a specific antinitrotyrosine antibody, also showed intense staining, suggesting formation of peroxynitrite in the inner ear through the reaction of NO with O^–₂. Scanning electron-microscopic study showed that the ototoxic effects could be blocked with N-nitro-L-arginine methylester, a competitive inhibitor of NO synthase, with superoxide dismutase, an O^–₂ scavenger, and with ebselen, a scavenger of peroxynitrite. On the basis of these findings, it can be concluded that NO together with O^–₂, which form more reactive peroxynitrite, play an important role in GM ototoxicity in the guinea pig.

Intratympanic injection of bacterial lipopolysaccharide impaired caloric responses and caused severe and widespread morphological damage to vestibular end organs and the endolymphatic sac in the guinea pig. These effects could be blocked with N-nitro-L-arginine methylester, a competitive inhibitor of nitric oxide synthase, with superoxide dismutase, an O₂ scavenger, with dexamethasone, and with ebselen, a scavenger of peroxynitrite. These observations indicate that enhanced nitric oxide and superoxide production, resulting in formation of peroxynitrite, is probably an important factor responsible for the pathological damage to vestibuli. If this is so, we may have found a way to study vestibular pathogenesis in inner ear disease.

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The purpose of this study was to investigate the occurrence of reactive oxygen species and peroxynitrite in the vestibular organ of the guinea pig following inoculation with bacterial lipopolysaccharide (LPS). The animals were injected transtympanically with 1 mg of LPS 24 h after the intraperitoneal injection of 0.1 mg LPS. Forty-eight hours after the inoculation, varying degrees of degeneration of the vestibular end organs were observed. Immunohistochemical study revealed immunoreactivity to xanthine oxidase (which generates O^–₂) in the vestibular organ after inoculation with LPS. Immunohistochemical investigation with a specific antinitrotyrosine antibody also showed intense staining of sensory epithelium, fluid transporting cells and the endolymphatic sac, suggesting formation of peroxynitrite in the vestibular organ through the reaction of NO with O^–₂. On the basis of these data, it can be concluded that NO together with O^–₂, which form more reactive peroxynitrite, may be the most important pathogenic agents in LPS-induced labyrinthitis in the guinea pig.