Decreased phagocytic function in neutrophils and monocytes from peripheral blood in periodontal disease

Assessing the Correlation of Periodontal Inflamed Surface Area (PISA) With Systemic Inflammatory Markers

Background Periodontitis has a vital role in eliciting a cross-reactivity or systemic inflammatory response, making periodontal inflamed surface area (PISA) a primary contributor to the inflammatory burden posed by periodontitis. PISA helps in the quantification of the amount of inflamed periodontal tissue. However, the existing literature data concerning PISA as an indicator of inflammatory burden are scarce, with limited research on the relationship between systemic inflammatory markers and PISA. Aim The present clinic-hematological cross-sectional study aimed to correlate PISA with systemic inflammatory markers. The study also aimed to assess serum concentrations of inflammatory markers such as erythrocyte sedimentation rates (ESR), C-reactive protein (CRP), and peripheral blood markers such as neutrophils and monocytes and to correlate these markers with PISA. Methods The study assessed 62 subjects, who were divided into two groups of 31 subjects, each following bleeding on probing (BOP) criteria. Group I consisted of subjects with generalized chronic gingivitis, and Group II included subjects with generalized chronic periodontitis. In two groups, BOP, probing pocket depth, clinical attachment level, and gingival recession were assessed along with PISA by a custom-made R function derived from a pre-existing, freely available MS Excel spreadsheet (Microsoft Corporation, Redmond, Washington). The results of the assessment were then compared. Results A statistically highly significant positive correlation was seen in PISA and CRP with a correlation coefficient of 0.4875 and p-value of 0.000059. A similar statistically significant positive correlation was seen in ESR and PISA with a correlation coefficient of 0.4089 and p-value of 0.000968. A statistically non-significant correlation was seen in neutrophils and PISA with p=0.576018. However, a moderate and positive statistically significant association was seen in monocyte and PISA with a correlation coefficient of 0.3258 and p-value of 0.009956. Conclusions The present study concludes that most of the common systemic inflammatory markers have a positive correlation with PISA. However, more studies are required to establish this correlation.

Quantitative Analysis of Phagocytosis in Whole Blood Using Double Staining and Visualization

Phagocytosis is an essential innate immunity function in humans and animals. A decrease in the ability to phagocytize is associated with many diseases and aging of the immune system. Assessment of phagocytosis dynamics requires quantification of bacteria inside and outside the phagocyte. Although flow cytometry is the most common method for assessing phagocytosis, it does not include visualization and direct quantification of location of bacteria. Here, we used double-labeled Escherichia coli cells to evaluate phagocytosis by flow cytometry (cell sorting) and confocal microscopy, as well as employed image cytometry to provide high-throughput quantitative and spatial recognition of the double-labeled E. coli associated with the phagocytes. Retention of pathogens on the surface of myeloid and lymphoid cells without their internalization was suggested to be an auxiliary function of innate immunity in the fight against infections. The developed method of bacterial labeling significantly increased the accuracy of spatial and quantitative measurement of phagocytosis in whole blood and can be recommended as a tool for phagocytosis assessment by image cytometry.

Recovery of the Decreased Phagocytic Function of Peripheral Monocytes and Neutrophil Granulocytes following Cytoreductive Surgery in Advanced Stage Epithelial Ovarian Cancer

(1) Monocytes and neutrophil granulocytes are the phagocytic cells of the innate immune system, playing a crucial role in recognizing and eliminating tumor-transformed cells. Our objective was to assess the impact of advanced-stage epithelial ovarian cancer (EOC) and cytoreductive surgery on the phagocytic function of peripheral monocytes and neutrophil granulocytes. We aimed to compare the pre- and postoperative phagocytic function of these immune cells in EOC patients with healthy control women. Additionally, we aimed to examine the influence of surgery on phagocytic function by comparing pre- and postoperative samples from patients with benign gynecological tumors. (2) We examined peripheral blood samples from 20 patients with FIGO IIIC stage high-grade serous EOC and 16 patients with benign gynecological tumors as surgical controls, collected before and seven days after tumor removal surgery, and from 14 healthy women. After separation, the cells were incubated with Zymosan-A particles, and the phagocytic index (PI) was assessed using immunofluorescence microscopy. One-way ANOVA, the Kruskal-Wallis H-test, and the paired samples t-test were used for the statistical analysis of the data. A significance level of p < 0.05 was applied. (3) Peripheral monocytes and neutrophils from EOC patients exhibited significantly lower preoperative PI values compared to healthy controls (p < 0.001; p < 0.001, respectively). Following cytoreductive surgery, the PI values of immune cells in EOC patients significantly increased by the 7th postoperative day (p < 0.001; p < 0.001), reaching levels comparable to those of healthy controls (p = 0.700 and p = 0.991). In contrast, there was no significant disparity in the PI values of cells obtained from pre- and postoperative blood samples of surgical controls when compared to healthy women (monocytes: p = 0.361 and p = 0.303; neutrophils: p = 0.150 and p = 0.235). (4) EOC and/or its microenvironment may produce factors that reduce the phagocytic function of monocytes and neutrophils, and the production of these factors may be reduced or eliminated after tumor removal.

The indicative role of inflammatory index in the progression of periodontal attachment loss

OBJECTIVE

To explore the forewarning immunological indicators during periodontal attachment loss progression in American adults.

METHODS

A total of 5744 participants with periodontal attachment loss were enrolled from the National Health and Nutrition Examination Surveys (NHANES) 2009-2014. In which, dependent variable was the counts of teeth with severe attachment loss (depth of periodontal probing was above 5 mm). Independent variables were circulatory immunological indexes, including counts of white blood cells (WBC), Lymphocytes, Monocytes, Neutrophils, Eosinophils, and Basophils. The association among variables was examined using multivariable linear regression models, fitting with smoothing curves, and generalizing additive models.

RESULTS

Based on the indicators of 5744 subjects, we found that severe attachment loss tended to occur in the elderly or males and was accompanied by higher WBC, Monocytes, and Neutrophils, as well as lower poverty-income ratio and educational qualification. WBC (above the inflection point: 6200 cells/µL) and Neutrophils (above the inflection point: 3300 cells/µL) counts were positively associated with attachment loss progression in each multivariable linear regression model. On subgroup analyses, stratified by sex and race, the positive correlation of WBC or Neutrophils with severe attachment loss was stable in both men and women, as well as in all races except blacks (WBC β = - 0.0576, 95% CI - 0.1945 to 0.0793, Neutrophils β = - 0.0527, 95% CI - 0.2285 to 0.1231).

CONCLUSION

Increasing WBC (above 6200 cells/µL) and Neutrophils (above 3300 cells/µL) counts were risk indicators of severe periodontal attachment loss among all races, except in blacks.

The effect of the "Oral-Gut" axis on periodontitis in inflammatory bowel disease: A review of microbe and immune mechanism associations

Periodontitis and inflammatory bowel diseases (IBD) are inflammatory diseases of the gastrointestinal tract that share common features of microbial-induced ecological dysregulation and host immune inflammatory response. The close relationship between periodontitis and IBD is characterized by a higher prevalence of IBD in patients with periodontitis and a higher prevalence and severity of periodontitis in patients with IBD, indicating that periodontitis and IBD are different from the traditional independent diseases and form an "Oral-Gut" axis between the two, which affect each other and thus form a vicious circle. However, the specific mechanisms leading to the association between the two are not fully understood. In this article, we describe the interconnection between periodontitis and IBD in terms of microbial pathogenesis and immune dysregulation, including the ectopic colonization of the gut by pathogenic bacteria associated with periodontitis that promotes inflammation in the gut by activating the host immune response, and the alteration of the oral microbiota due to IBD that affects the periodontal inflammatory response. Among the microbial factors, pathogenic bacteria such as Klebsiella, Porphyromonas gingivalis and Fusobacterium nucleatum may act as the microbial bridge between periodontitis and IBD, while among the immune mechanisms, Th17 cell responses and the secreted pro-inflammatory factors IL-1β, IL-6 and TNF-α play a key role in the development of both diseases. This suggests that in future studies, we can look for targets in the "Oral-Gut" axis to control and intervene in periodontal inflammation by regulating periodontal or intestinal flora through immunological methods.

Trichinella spiralis excretory-secretory antigens selectively inhibit the release of extracellular traps from neutrophils without affecting their additional antimicrobial functions

Neutrophil extracellular traps (NETs) are fiber structures composed of chromatin and granular proteins that capture and eliminate microorganisms. The NETs formation is induced in response to pathogens and physiological stimuli; however, some pathogens have developed strategies to evade NETs activity. Trichinella spiralis excretory-secretory (ES) antigens are proteins that allow the establishment of the parasite in the host, facilitating penetration, migration, nutrition, and survival. In this paper we described that ES antigens inhibit NETs release, since neutrophils incubated with these antigens maintains a delobulated nucleus, without the release fibers structures indicative of NETs. We also found that other antimicrobial functions of neutrophils, such as phagocytic activity, degranulation, and ROS production, remain unchanged after incubation with ES antigens. This is relevant since it could constitute a novel strategy for the treatment of autoimmune pathologies in which the formation of NETs performs an important role.

Circulating inflammatory cell profiling and periodontitis: A systematic review and meta-analysis

Inflammation is a key driver of common noncommunicable diseases. Among common triggers of inflammation, chronic gingival inflammation (periodontitis) triggers a consistent humoral host inflammatory response, but little is known on its impact on circulating inflammatory cell profiles. We aimed to systematically appraise all the evidence linking periodontitis and its treatment to circulating inflammatory cell profiles. From 6 databases, 157 studies were eligible for qualitative synthesis and 29 studies for meta-analysis. Our meta-analysis showed that participants with periodontitis exhibited a significant mean increase in circulating CD4⁺ , CD4⁺ CD45RO⁺ , IFNγ-expressing CD4⁺ and CD8⁺ T cells, CD19⁺ CD27⁺ and CD5⁺ B cells, CD14⁺ CD16⁺ monocytes, and CD16⁺ neutrophils but decrease in CD8⁺ T and CD14⁺⁺ CD16^- monocytes. Our qualitative synthesis revealed that peripheral blood neutrophils of patients with periodontitis consistently showed elevated production of reactive oxygen species (ROS) when compared with those of healthy controls. Some evidence suggested that the treatment of periodontitis reversed the exaggerated ROS production, but limited and inconclusive data were found on several circulating inflammatory cell profiling. We conclude that periodontitis and its treatment are associated with minor but consistent alterations in circulating inflammatory cell profiles. These changes could represent key mechanisms explaining the association of periodontitis with other comorbidities such as cardiovascular disease, diabetes, and rheumatoid arthritis.

Immunomodulation in the Treatment of Periodontitis: Progress and Perspectives

Periodontitis is one of the most common dental diseases. Compared with healthy periodontal tissues, the immune microenvironment plays the key role in periodontitis by allowing the invasion of pathogens. It is possible that modulating the immune microenvironment can supplement traditional treatments and may even promote periodontal regeneration by using stem cells, bacteria, etc. New anti-inflammatory therapies can enhance the generation of a viable local immune microenvironment and promote cell homing and tissue formation, thereby achieving higher levels of immune regulation and tissue repair. We screened recent studies to summarize the advances of the immunomodulatory treatments for periodontitis in the aspects of drug therapy, microbial therapy, stem cell therapy, gene therapy and other therapies. In addition, we included the changes of immune cells and cytokines in the immune microenvironment of periodontitis in the section of drug therapy so as to make it clearer how the treatments took effects accordingly. In the future, more research needs to be done to improve immunotherapy methods and understand the risks and long-term efficacy of these methods in periodontitis.

Gingival crevicular fluid infiltrating CD14+ monocytes promote inflammation in periodontitis

Periodontitis is a condition that occurs because of inflammation-mediated tissue degeneration. Many studies have been conducted to identify inflammatory molecules in periodontitis, but the well-defined role of cells from the immune system in the progression of periodontitis as well as in gingival tissue degeneration has not been appropriately established. The objective of the present study was to characterize the monocytes isolated from the gingival crevicular fluid (GCF) in patients with periodontitis. GCF was obtained from periodontitis patients and healthy controls. Cytokine levels of CCL2 were evaluated by ELISA in GCF samples. CD14+ monocytes were separated using magnetic sorting from GCF. RT-qPCR was performed to assess the gene expression. Cytometric bead array analysis was performed to analyze the levels of cytokines and chemokines in the secretome of cells. CD14+ monocytes from GCF secreted higher levels of CCL2 and showed elevated expression of genes responsible for monocyte migration. Additionally, upon lipopolysaccharide stimulation, these monocytes secreted higher levels of inflammatory cytokines and chemokines. This investigation aids in understanding the inflammatory microenvironment of periodontitis by characterizing GCF in terms of infiltrated CD14+ monocytes, cytokines, and molecules secreted by these monocytes, which are specific for cellular differentiation.

Synthetic cell-permeable caveolin-1 scaffolding domain peptide activates phagocytosis of Escherichia coli by regulating Rab5 activity

Caveolae are defined as 50-100 nm wide pits in the plasma membrane containing oligomeric caveolin proteins. They have been implicated in endocytosis (including phagocytosis), transcytosis, calcium signalling, and numerous other signal transduction events. Caveolin-1, a major structural component of caveolae, enhances Rab5 activity. In this study, we examined the effect of a synthetic cell-permeable peptide of the caveolin-1 scaffolding domain (CSD) on phagocytosis. Treatment with the CSD peptide increased Rab5 activity, Rab5-early endosome antigen 1 (EEA1) interaction, and phagocytosis of Escherichia coli. The results suggest that the synthetic cell-permeable CSD peptide is an activator of phagocytosis.

Reactive oxygen species-mediated cytoplasmic stiffening impairs the phagocytic ability of the macrophage

The phagocytic ability of macrophages empowers them to enforce innate immunity. RAW264.7, THP-1 and peripheral blood mononuclear cell-derived macrophages display considerable variability with regards to their phagocytic ability. We identify the underlying causes that attenuate the phagocytic abilities of a macrophage. Deformability of the cytoplasm and cortex influences the macrophage's phagocytic ability, and macrophages use the large cell-to-cell variability of their cytoplasmic stiffness to modulate their phagocytic ability. We find that the more-deformable macrophages have a higher phagocytic ability than those that are less deformable. Further, the subcellular spatial variability of cortex stiffness gives rise to more-deformable subdomains on the membrane for pathogen ingestion. We report a previously unknown negative-feedback loop that is triggered by the phagocytic oxidative burst. Macrophages utilize the excess reactive oxygen species to stiffen the cytoplasm, reducing their phagocytic propensity. In organisms, ageing or pathological conditions impair the phagocytic ability of macrophages. Our findings identify the targets that could potentially be utilized for restoring the phagocytic ability of the defunct macrophages.

A brief history of periodontics in the United States of America: Pioneers and thought-leaders of the past, and current challenges

This paper summarizes historical events in periodontology in the United States over the past 200 years. The contributions of some of the key thought-leaders of the past are highlighted. Throughout the 20th century, the evolution of thought, leading to the views currently held regarding the pathogenesis and treatment of periodontal diseases, was significantly influenced by: (1) major changes in health-care education; (2) the emergence of periodontics as a specialty of dentistry; (3) the publication of peer-reviewed journals with an emphasis on periodontology; (4) formation of the National Institute of Dental and Craniofacial Research (NIDCR); and (5) expansion of periodontal research programs by the NIDCR. The two major future challenges facing periodontal research are development of a better understanding of the ecological complexities of host-microbial interactions in periodontal health and disease, and identification of the relevant mechanisms involved in the predictable regeneration of damaged periodontal tissues.

Toll-like receptor-2 and -4 responses regulate neutrophil infiltration into the junctional epithelium and significantly contribute to the composition of the oral microbiota

BACKGROUND

Oral gingival tissue, especially the junctional epithelium (JE), is constantly exposed to sub-gingival plaque. A key component of gingival health is the regulation of the number of neutrophils that migrate into the gingival crevice to counteract its harmful effects. This report investigates the contribution of innate defense receptors, Toll-like receptor (TLR)2, TLR4, and both (TLR2/4) to the maintenance of neutrophil homeostasis in the JE.

METHODS

Bacterial composition was analyzed from whole oral swabs collected from 12- to 14-week-old TLR2, TLR4, TLR2/4 double knock-out (KO) mice using a MiSeq platform targeting the V3-V4 region of the 16S ribosomal RNA gene. Mandibles were histologically examined for quantification of neutrophils in the JE and bone loss. Lastly, total bacterial load was quantitated using quantitative real-time PCR.

RESULTS

Compared with wild-type, all TLR KO mice displayed significantly increased recruitment of neutrophils (P = 0.0079) into the JE. In addition, TLR4 and TLR2/4 KO mice demonstrated a significant increase in the number of bacteria (P = 0.0022 and P = 0.0152, respectively). Lastly, comparative compositional analyses of the oral microbiome revealed that each KO strain harbored unique microbial communities that are distinct from each other but maintained similar levels of alveolar bone.

CONCLUSIONS

Neutrophil migration into healthy mouse JE does not require TLR2 or TLR4. However, a significant increase in the number of neutrophils as well as a significant change in the oral microbial composition in both TLR2 and TLR4 KO mice demonstrate that these TLRs contribute to the homeostatic relationship between bacteria and the host in healthy mice periodontal tissue.

Distal Consequences of Oral Inflammation

Periodontitis is an incredibly prevalent chronic inflammatory disease, which results in the destruction of tooth supporting structures. However, in addition to causing tooth and alveolar bone loss, this oral inflammatory disease has been shown to contribute to disease states and inflammatory pathology at sites distant from the oral cavity. Epidemiological and experimental studies have linked periodontitis to the development and/or exacerbation of a plethora of other chronic diseases ranging from rheumatoid arthritis to Alzheimer's disease. Such studies highlight how the inflammatory status of the oral cavity can have a profound impact on systemic health. In this review we discuss the disease states impacted by periodontitis and explore potential mechanisms whereby oral inflammation could promote loss of homeostasis at distant sites.

Comparison of the effects of adipose tissue mesenchymal stromal cell-derived exosomes with conditioned media on neutrophil function and apoptosis

BACKGROUND

Neutrophils are short-lived cells of the innate immune system that have an important role in defending against pathogens by producing reactive oxygen species (ROS). Therefore, effective strategies for increasing neutrophil's viability and function may be beneficial, especially in many conditions such as infections and immunodeficiency diseases. Some studies suggest using multipotent mesenchymal stromal cells (MSCs) and MSC-conditioned media (MSC-CM) for this aim. But, there is no study on using MSC-derived exosomes for improving neutrophil's viability and function. So, we examined the effects of MSC-exosomes and also MSC-CM on neutrophil's function and survival and compared them with each other.

METHODS

Exosomes and CM were isolated from human adipose tissue MSCs. Exosomes were characterized, and the protein content of them was determined. Neutrophils were isolated from five healthy donors, and the effects of the two independent treatments (exosomes and conditioned media) on neutrophil's apoptosis were measured by Annexin V-PI method, then neutrophil's function was evaluated using NBT and phagocytosis assays.

RESULTS

It was recognized that exosomes decreased neutrophils apoptosis and increased their phagocytosis capacity. The conditioned media augmented neutrophil's phagocytosis and reactive oxygen species (ROS) production, but it couldn't decrease neutrophil's apoptosis.

DISCUSSION

Briefly, we concluded that MSC-exosomes augment neutrophil's viability more than their function while MSC-CM increase neutrophil's function more than the survival. This report showed that the use of MSC-exosomes and CM might be useful for increasing immunity by improving neutrophil's function and survival.

Oral Neutrophils Characterized: Chemotactic, Phagocytic, and Neutrophil Extracellular Trap (NET) Formation Properties

Maintenance of oral health is in part managed by the immune-surveillance and antimicrobial functions of polymorphonuclear leukocytes (PMNs), which migrate from the circulatory system through the oral mucosal tissues as oral PMNs (oPMNs). In any microorganism-rich ecosystem, such as the oral cavity, PMNs migrate toward various exogenous chemoattractants, phagocytose bacteria, and produce neutrophil extracellular traps (NETs) to immobilize and eliminate pathogens. PMNs obtained from the circulation through venipuncture (hereafter called cPMNs) have been widely studied using various functional assays. We aimed to study the potential of oPMNs in maintaining oral health and therefore compared their chemotactic and antimicrobial functions with cPMNs. To establish chemotactic, phagocytic, and NET forming capacities, oPMNs and cPMNs were isolated from healthy subjects without obvious oral inflammation. Directional chemotaxis toward the chemoattractant fMLP was analyzed using an Insall chamber and video microscopy. fMLP expression was assessed by flow cytometry. Phagocytosis was analyzed by flow cytometry, following PMN incubation with heat-inactivated FITC-labeled micro-organisms. Furthermore, agar plate-based killing assays were performed with Escherichia coli (Ec). NET formation by oPMNs and cPMNs was quantified fluorimetrically using SYTOX™ Green, following stimulation with either PMA or RPMI medium (unstimulated control). In contrast to cPMNs, the chemotactic responses of oPMNs to fMLP did not differ from controls (mean velocity ± SEM of cPMNs: 0.79 ± 0.24; of oPMNs; 0.10 ± 0.07 micrometer/min). The impaired directional movement toward fMLP by oPMNs was explained by significantly lower fMLP receptor expression. Increased adhesion and internalization of various micro-organisms by oPMNs was observed. oPMNs formed 13 times more NETs than stimulated cPMNs, in both unstimulated and stimulated conditions. Compared to cPMNs, oPMNs showed a limited ability for intracellular killing of Ec. In conclusion, oPMNs showed exhausted capacity for efficient chemotaxis toward fMLP which may be the result of migration through the oral tissues into the oral cavity, being a highly “hostile” ecosystem. Overall, oPMNs' behavior is consistent with hyperactivity and frustrated killing. Nevertheless, oPMNs most likely contribute to maintaining a balanced oral ecosystem, as their ability to internalize microbes in conjunction with their abundant NET production remains after entering the oral cavity.

[Immunomodulating activity of adhesive dental film containing chlorhexidine and ketoprofen in serum of patients with chronic periodontitis]

The study was carried out in series of preclinical tests of new adhesive dental film developed for local treatment of inflammatory periodontal disease and containing chlorhexidine bigluconate and ketoprofen. The aim of the work was to determine film's effect on the activity of blood neutrophils in healthy individuals and in patients with chronic periodontitis using luminol-dependent chemiluminescence method. The investigated dental film showed modulating influence on blood phagocytes methabolism depending on their initial functional state. Immunomodulating activity revealed is associated with the polymer base and is potentiated by ketoprofen in case of hyporeactive inflammation.

Is periodontitis a comorbidity of COPD or can associations be explained by shared risk factors/behaviors?

COPD is recognized as having a series of comorbidities potentially related to common inflammatory processes. Periodontitis is one of the most common human inflammatory diseases and has previously been associated with COPD in numerous observational studies. As periodontitis and COPD are both chronic, progressive conditions characterized by neutrophilic inflammation with subsequent proteolytic destruction of connective tissue, it has been proposed that they share common pathophysiological processes. The mechanisms proposed to link COPD and periodontitis include mechanical aspiration of oral contents into the respiratory tree, overspill of locally produced inflammatory mediators into the systemic circulation or oral or lung-derived bacteremia activating an acute-phase response and also reactive oxygen species (ROS) and cytokine release by systemic neutrophils at distant sites. Studies of systemic neutrophils in COPD and chronic periodontitis describe altered cellular functions that would predispose to inflammation and tissue destruction both in the lung and in the mouth, again potentially connecting these conditions. However, COPD and periodontitis also share risk factors such as age, chronic tobacco smoke exposure, and social deprivation that are not always considered in observational and interventional studies. Furthermore, studies reporting associations have often utilized differing definitions of both COPD and periodontitis. This article reviews the current available evidence supporting the hypothesis that COPD and inflammatory periodontal disease (periodontitis) could be pathologically associated, including a review of shared inflammatory mechanisms. It highlights the potential limitations of previous studies, in particular, the lack of uniformly applied case definitions for both COPD and periodontitis and poor recognition of shared risk factors. Understanding associations between these conditions may inform why patients with COPD suffer such a burden of comorbid illness and new therapeutic strategies for both the diseases. However, further research is needed to clarify factors that may be directly causal as opposed to confounding relationships.

CX3CR1hi Monocyte/Macrophages Support Bacterial Survival and Experimental Infection-Driven Bone Resorption

Porphyromonas gingivalis,an anaerobic bacterium strongly linked to infection-driven inflammatory bone erosion, thrives within a highly inflamed milieu and disseminates to distant sites, such as atherosclerotic plaque. We examined the role of monocyte/macrophages in determining the outcome of infection with P. gingivalis. Surprisingly, transient monocyte/macrophage depletion led to greatly improved clearance of P. gingivalis. The chemokine receptors CCR2 and CX3CR1 play a major role in monocyte recruitment and differentiation to Ly6C(hi) vs CX3CR1(hi) subsets, respectively. To determine the contribution of particular monocyte/macrophage subsets to bacterial survival, we challenged chemokine receptor knockout mice and found that P. gingivalis clearance is significantly improved in the absence of CX3CR1. CX3CR1(hi) monocyte/macrophages promote P. gingivalis survival by downregulating neutrophil phagocytosis. Furthermore, CX3CR1 knockout mice resist bone resorption in the oral cavity following challenge with P. gingivalis Our findings provide an explanation for bacterial coexistence alongside an activate neutrophil infiltrate.

Impaired neutrophil extracellular trap formation: a novel defect in the innate immune system of aged individuals

Neutrophil extracellular traps (NETs) are a recently discovered addition to the defensive armamentarium of neutrophils, assisting in the immune response against rapidly dividing bacteria. Although older adults are more susceptible to such infections, no study has examined whether aging in humans influences NET formation. We report that TNF-α-primed neutrophils generate significantly more NETs than unprimed neutrophils and that lipopolysaccharide (LPS)- and interleukin-8 (IL-8)-induced NET formation exhibits a significant age-related decline. NET formation requires generation of reactive oxygen species (ROS), and this was also reduced in neutrophils from older donors identifying a mechanism for reduced NET formation. Expression of IL-8 receptors (CXCR1 and CXCR2) and the LPS receptor TLR4 was similar on neutrophils from young and old subjects, and neutrophils challenged with phorbol-12-myristate-13-acetate (PMA) showed no age-associated differences in ROS or NET production. Taken together, these data suggest a defect in proximal signalling underlies the age-related decline in NET and ROS generation. TNF-α priming involves signalling through p38 MAP kinase, but activation kinetics were comparable in neutrophils from young and old donors. In a clinical setting, we assessed the capacity of neutrophils from young and older patients with chronic periodontitis to generate NETs in response to PMA and hypochlorous acid (HOCL). Neutrophil extracellular trap generation to HOCL, but not PMA, was lower in older periodontitis patients but not in comparison with age-matched controls. Impaired NET formation is thus a novel defect of innate immunity in older adults but does not appear to contribute to the increased incidence of periodontitis in older adults.