Recent evidence suggests that complement and Toll-like receptors (TLRs) crosstalk to coordinate innate immunity. We report a novel immune subversion mechanism involving microbial exploitation of the ability of complement and TLRs for communication. Porphyromonas gingivalis, a major oral and systemic pathogen expressing complement C5 convertase-like activity, was shown to synergize with C5a for cAMP elevation resulting in macrophage immunosuppression and enhanced pathogen survival in vitro and in vivo. The cAMP synergy strictly required TLR2 signaling and a pertussis toxin- and thapsigargin-sensitive C5a receptor pathway, whereas protein kinase A and glycogen synthase kinase-3β acted as downstream effectors. Antagonistic blockade of the C5a receptor abrogated this evasive strategy and may thus have important therapeutic implications in periodontitis and atherosclerosis, where P. gingivalis is implicated. This first demonstration of complement-TLR crosstalk for immunosuppressive cAMP signaling indicates that pathogens may not simply undermine complement and/or TLRs as separate entities, but may also exploit their crosstalk pathways.

The C5a anaphylatoxin receptor (C5aR; CD88) is activated as part of the complement cascade and exerts important inflammatory, antimicrobial, and regulatory functions, at least in part, via crosstalk with TLRs. However, the periodontal pathogen Porphyromonas gingivalis can control C5aR activation by generating C5a through its own C5 convertase-like enzymatic activity. In this paper, we show that P. gingivalis uses this mechanism to proactively and selectively inhibit TLR2-induced IL-12p70, whereas the same pathogen-instigated C5aR-TLR2 crosstalk upregulates other inflammatory and bone-resorptive cytokines (IL-1β, IL-6, and TNF-α). In vivo, the ability of P. gingivalis to manipulate TLR2 activation via the C5a-C5aR axis allowed it to escape IL-12p70–dependent immune clearance and to cause inflammatory bone loss in a murine model of experimental periodontitis. In the latter regard, C5aR-deficient or TLR2-deficient mice were both resistant to periodontal bone loss, in stark contrast with wild-type control mice, which is consistent with the interdependent interactions of C5aR and TLR2 in P. gingivalis immune evasion and induction of bone-resorptive cytokines. In conclusion, P. gingivalis targets C5aR to promote its adaptive fitness and cause periodontal disease. Given the current availability of safe and effective C5aR antagonists, pharmacological blockade of C5aR could act therapeutically in human periodontitis and reduce associated systemic risks.

Although periodontal infection does affect the concentration of hs-CRP and IL-6 in serum, a subgroup of patients exist who are highly susceptible to an increased risk of CHD associated with periodontitis, suggesting that there may be subjects who have an elevated risk of CHD independent of susceptibility to periodontal tissue destruction per se.

SummaryThe balance between inflammatory mediators and their counter-regulatory molecules may be crucial for determining the outcome of immune pathology of periodontal diseases. Based on clinical and immunological findings, the immune response in stable gingivitis lesion is supposed to be in balance, whereas the response is skewed towards the predominance of proinflammatory reactivity in progressive periodontitis lesion. However, this hypothesis has not been verified. Therefore, the aim of this study was to compare the gene expression profile of inflammatory mediators including proinflammatory cytokines and other inflammatory molecules, and anti-inflammatory cytokines by using quantitative real-time polymerase chain reaction in gingivitis and periodontitis lesions showing distinct clinical entities. For inflammatory mediators, interleukin (IL)-1β β β β , interferon (IFN)-γ γ γ γ and receptor activator of nuclear factor (NF)-κ κ κ κ B ligand tended to be higher in periodontitis, whereas tumour necrosis factor (TNF)-α α α α and IL-12 p40 showed no difference. Heat-shock protein 60 (HSP60) expression was up-regulated significantly in periodontitis. For anti-inflammatory cytokines, transforming growth factor (TGF)-β β β β 1 expression tended to be higher in periodontitis compared with gingivitis, whereas no difference was observed for IL-10 and IL-4. These findings support further our previous finding that autoimmune response to HSP60 may exert in periodontitis lesion, and suggest that perhaps subtle differences in the balance of cytokines may result in different disease expression.

Background and objective-Young mice do not develop measurable periodontal bone loss, unless heavily infected with human periodontal pathogens. However, mice with genetically altered immune system are unable to control their own oral flora and develop periodontitis early in life. Based on the potential of the indigenous oral microbiota to cause periodontitis, we hypothesized that normal mice may ultimately develop inflammatory periodontal bone loss, i.e., as a function of age. If confirmed, this could serve as an aging model of chronic periodontitis.

The impact of ageing in innate immunity is poorly understood. Studies in the mouse model have described altered innate immune functions in aged macrophages, although these were not generally linked to altered expression of receptors or regulatory molecules. Moreover, the influence of ageing in the expression of these molecules has not been systematically examined. We investigated agedependent expression differences in selected Toll-like and other pattern-recognition receptors, receptors involved in inflammatory amplification, and in transmembrane and intracellular regulators of inflammatory signaling. Young and aged macrophages were examined under resting conditions or upon activation with Porphyromonas gingivalis, a major pathogen in periodontal disease, the prevalence and severity of which increase in old age. We detected a limited number of age-dependent alterations, involving both reduction and increase of immune activity. Interestingly, surface expression of receptors that amplify inflammation (C5a anaphylatoxin receptor and triggering receptor expressed on myeloid cells [TREM]-1) was elevated in aged macrophages. No significant age-dependent differences were observed regarding the phagocytosis and intracellular killing of P. gingivalis, consistent with lack of significant changes in phagocytic receptor expression and induction of antimicrobial molecules. Therefore, at least at the cellular level, certain aspects of innate immune function may not necessarily decline with age.

SummarySeveral reports have demonstrated a possible association of periodontal infections with coronary heart disease (CHD) by elevated antibody titre to periodontopathic bacteria in CHD patients compared with non-diseased controls. Although each periodontopathic bacterium may vary in virulence for periodontitis and atherosclerosis, antibody response to multiple bacteria in CHD patients has not been understood fully. Therefore, serum levels of antibody to 12 periodontopathic bacteria together with other atherosclerotic risk markers were compared among 51 patients with CHD, 55 patients with moderate to severe chronic periodontitis and 37 healthy individuals. The antibody response was the most prevalent for Porphyromonas gingivalis, a major causative organism, in CHD as well as periodontitis patients. However, antibody positivity was different between CHD and periodontitis if the response was analysed for two different strains of P. gingivalis, namely FDC381 and Su63. While periodontitis patients were positive for both P. gingivalis FDC381 and Su63, a high frequency of antibody positivity for P. gingivalis Su63 but not for FDC381 was observed in CHD patients. The results indicate that the presence of particular periodontopathic bacteria with high virulence may affect atherogenesis. Identifying the virulence factors of P. gingivalis Su63 may gain insight into the new therapeutic modality for infection-induced deterioration of atherosclerosis.

Streptococcus pneumoniae is a leading cause of bacterial pneumonia and is the principal cause of morbidity and mortality worldwide. Previous studies suggested that excessive activation of neutrophils results in the release of neutrophil elastase, which contributes to lung injury in severe pneumonia. Although both pneumococcal virulence factors and neutrophil elastase contribute to the development and progression of pneumonia, there are no studies analysing relationships between these factors. Here, we showed that pneumolysin, a pneumococcal pore-forming toxin, induced cell lysis in primary isolated human neutrophils, leading to the release of neutrophil elastase. Pneumolysin exerted minimal cytotoxicity against alveolar epithelial cells and macrophages, whereas neutrophil elastase induced detachment of alveolar epithelial cells and impaired phagocytic activity in macrophages. Additionally, activation of neutrophil elastase did not exert bactericidal activity against S. pneumoniae in vitro. P2X7 receptor, which belongs to a family of purinergic receptors, was involved in pneumolysin-induced cell lysis. These findings suggested that infiltrated neutrophils are the primary target cells of pneumolysin, and that S. pneumoniae exploits neutrophil-elastase leakage to induce the disruption of pulmonary immune defences, thereby causing lung injury.