Peripheral blood neutrophils from chronic periodontitis (CP) patients exhibit a hyper-reactive phenotype in terms of production of reactive oxygen species (ROS) and show up-regulation of a group of interferon (IFN)-stimulated genes (ISG's; Wright et al. J Dent Res 2005, 84: abstr 0014). Objective: To investigate the role of interferons in neutrophil hyper-reactivity in chronic periodontitis. Methods: Peripheral blood neutrophils were prepared from 5 non-smoking healthy volunteers and primed with E. coli LPS (0.1mg/1x10⁵ cells) or IFNa, IFNb, IFNg (25IU/1x10⁵ cells). After 30mins the total production (luminol) or extracellular release (isoluminol) of ROS was determined using chemiluminescence, with and without Fcg-receptor (FcgR) stimulation with opsonised S. aureus (NCTC6571; 300 bacteria/neutrophil). After a further 2.5hrs RNA (phenol-chloroform extraction) was prepared and RT-PCR performed for 6 ISG's (Mx1, IFIT4, G1P2, IFIT1, cig5, IFI44-like) using pooled RNA. IFNa levels were determined by ELISA (Amersham Biosciences) in plasma from 10 CP patients, who exhibited neutrophil hyper-responsivity to FcgR stimulation (Wright et al. J Dent Res 2004, 83: abstr 1088), and age/sex/smoking-matched controls. Paired data were analysed by 1-tailed Wilcoxon and INFa levels by Mann-Whitney test. Results: Enhancement of total and extra-cellular FcgR-stimulated chemiluminescence by neutrophils was induced by priming with IFNa (41±20%, P=0.031; 32±28%, P=0.031), IFNb (38±13%, P=0.031; 20±19%, P=0.063), IFNg (43±12%, P=0.031; 26±20%, P=0.031) and LPS (29±21%, P=0.063; 20±21%, P=0.094). RT-PCR analysis showed that IFNa and IFNb priming increased expression of all 6 ISG's by 49-209%. Priming with IFNg or LPS increased expression of 5 ISG's by 9-101%. IFI44-like and Mx1 gene expression was unaffected by IFNg and LPS priming respectively. Plasma IFNa levels in CP subjects (2.02±0.96pg/ml) were higher than healthy controls (1.18±0.62pg/ml, P<0.05). Conclusion: Type I interferons may be one determinant of the distinct molecular phenotype and hyper-reactivity exhibited by peripheral blood neutrophils in chronic periodontitis. Supported by MRC UK-G0000797.

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