2A and BB shows that MxA protein expression was clearly observed in the epithelial layer of periodontal tissue. Epithelial MxA immunoreactivity seemed to be stronger in basal and spinous layers than outermost layer of oral epithelium. Using semiquantitative scoring, there
was a significantly higher score of epithelial MxA in healthy group than periodontitis group (Table 1) (p = 0.012), thus highlighting the role of MxA protein in healthy perio-dontal tissue. Since MxA protein is known to be induced by type I and type III IFN [[27-29]], we then investigated the presence of type I and type III IFN in periodontal tissue. The mRNA expression of IFN-α, IFN-β, and IFN-λ in healthy BYL719 mouse periodontal tissue was negligible (n = 10, data not shown). The findings led us to hypothesize that other local mediators may be responsible for the observed MxA protein expression in healthy periodontal
tissue. Antimicrobial peptides including α-defensin, β-defensin, and LL-37 are constitutively expressed in healthy periodontal tissue [[30]] and these mediators could conceivably play a role in MxA expression. Furthermore, a recent study described a fish homologue of MxA protein which was induced by human α-defensin [[31]]. FDA approved Drug Library Therefore, we stimulated primary HGEC cultures with nontoxic concentrations of α-defensin-1, -2, and -3, β-defensin-1, -2, and -3, and LL-37. Fig. 3A shows that α-defensin-1, -2, and -3 markedly induced MxA protein in HGECs. There seemed to be stronger MxA staining in HGECs treated with α-defensin-1 than in those treated with α-defensin-2 and α-defensin-3. In contrast, β-defensin-1, -2, -3 and LL-37 induced only negligible MxA protein expression. IFN-α was used as positive control and induced strong MxA protein expression. The results of MxA protein expression induced by α-defensin-1, -2, and -3, β-defensin-1, -2, and -3, and LL-37 agree with mRNA expression using real-time RT-PCR (Fig. 3B). α-defensin-1 was also able to stimulate MxA protein expression in other cells including normal human bronchial epithelial cells and primary
human microvascular endothelial cells (Fig. 3C). Addition of neutralizing antibodies against type I IFN (IFN-α and IFN-β) into the cultures of α-defensin-1-treated HGECs had no effect on MxA expression whereas these neutralizing antibodies markedly inhibited MxA expression in IFN-α-treated HGECs (Fig. MG-132 purchase 3D). The IFN-α-induced MxA protein expression was likely to be independent on α-defensins since no detection of α-defensin production was observed in cultures of IFN-α-treated HGECs (Supporting Information Fig. 1). In addition, no production of type I IFN (IFN-α and IFN-β) was observed at both the mRNA and protein levels in α-defensin-treated HGECs (data not shown). Collectively, these data suggest that α-defensin and type I interferon use different triggering pathways to induce MxA expression. The antiviral activity of MxA against influenza A virus is well recognized [[25]].