Inducible nitric oxide synthase activity by interferon‐g‐producing cells in human radicular cysts

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Abstract
Aim In this study, the interaction of interferon‐γ‐ (IFN‐γ) and inducible nitric oxide synthase (iNOS)‐producing cells in human radicular cysts were investigated. Methodology Inflamed periapical tissues were obtained from patients at the time of endodontic surgical treatments and were cut into two pieces. After fixing with acetone or 4% paraformaldehyde in phosphate‐buffered saline, 5‐m‐thick paraffin and cryostat sections were prepared. The paraffin sections of the inflamed tissues were evaluated histologically with haematoxylineosin stains. The specimens diagnosed as radicular cysts were then examined by immunostaining. Immunohistochemistry for iNOS and fluoresence microscopy for IFN‐γ using the cryostat sections were performed with a mixture of affinity purified human iNOS antiserum and human IFN‐γ monoclonal antibodies. Results The results revealed that iNOS‐γ producing cells localized adjacent to IFN‐γ‐producing cells. In addition, some of iNOS‐producing cells exhibited immunoreactive IFN‐γ. On the other hand, epithelial cells showed significant levels of iNOS production, but not IFN‐γ. Conclusions The data would suggest the possibility that iNOS production could be precisely controlled by autocrine or paracrine effects of IFN‐γ producing cells in radicular cysts and might play a pivotal role in periapical lesions. These findings are consistent with a hypothesis suggesting that NO inhibitors could be used through the root canals as a pharmacological treatment for periapical lesions.