IL-17 C and its receptor IL-17 RA/ IL-17 RE identify human oral epithelial cell as an inflammatory cell in recurrent aphthous ulcer.

Background Recurrent aphthous ulcer ( RAU) is an ulcerative disease of non-keratinized oral mucosa. Colon and bronchial epithelial cells produce interleukin-17 C ( IL-17 C) upon stimulation of Toll-like receptor 2 ( TLR2), TLR3 and TLR5, which are highly expressed in epithelial cells in RAU lesions. We therefore investigated the eventual presence and function of IL-17 C in cultured human oral keratinocytes ( HOK) and control biopsies compared to RAU lesions. Methods Expression of IL-17 A, IL-17 C, IL-17 RA and IL-17 RE was analysed in cultured HOK cells using quantitative real-time polymerase chain reaction (q RT- PCR). HOK cells were stimulated with IL-17 C and analysed for IL-8 and tumour necrosis factor-α ( TNF-α) using q RT- PCR. Control mucosa ( n = 5) was immunostained for IL-17 A, IL-17 C, IL-8, TNF-α and mast cell tryptase and compared with RAU lesions ( n = 5) using the mean grey scale value. Results IL-17 C, but no IL-17 A, m RNA was found in cultured HOK cells. Components of the heterodimeric IL-17 RA/ IL-17 RE receptor for IL-17 C were also highly expressed. Stimulation of HOK with IL-17 C increased TNF-α m RNA ( P = 0.03; IL-8 increase was not statistically significant). HOK in RAU lesions stained intensively for IL-17 C compared to controls ( P = 0.006). This was associated with increased epithelial immunostaining of TNF-α ( P = 0.04) and IL-8 ( P = 0.02). Most of the inflammatory cells which stained for IL-17 A in control mucosa and RAU lesions were also mast cell tryptase positive. Conclusion IL-17 C is highly expressed in epithelial cells in RAU lesions, where it seems to stimulate oral keratinocytes via IL-17 RA/ IL-17 RE to produce pro-inflammatory cytokines. Human oral epithelial cells are probably important inflammatory cells in RAU. [ABSTRACT FROM AUTHOR]