Hepatocytes produce tumor necrosis factor-α and interleukin-6 in response to Porphyromonas gingivalis

Takano M, Sugano N, Mochizuki S, Koshi RN, Narukawa TS, Sawamoto Y, Ito K. Hepatocytes produce tumor necrosis factor‐α and interleukin‐6 in response to Porphyromonas gingivalis. J Periodont Res; 2012; 47: 89–94. © 2011 John Wiley & Sons A/S Background and Objective: The liver plays a major role in clearing systemic bacterial infections. In addition, inflammatory cytokines produced in the liver play a critical role in systemic cytokine levels. The aim of this study was to investigate the production of tumor necrosis factor‐α (TNF‐α) and interleukin‐6 (IL‐6) by hepatocytes in response to periodontal pathogens. Material and Methods: The mouse hepatic carcinoma cell line Hepa‐1.6 and the mouse macrophage‐like cell line RAW 264 were co‐cultured in Transwell insert plates. Cells were stimulated with bacterial extracts prepared from Porphyromonas gingivalis and the induction of TNF‐α and IL‐6 was measured using real‐time PCR and ELISA. Results: After stimulation with bacteria, the induction of TNF‐α and IL‐6 was observed in RAW 264 cells and Hepa‐1.6 cells. Significant reduction of TNF‐α mRNA expression in Hepa‐1.6 cells was observed after treatment with antibody to TNF‐α. Conclusion: The results obtained in the present study show that P. gingivalis extract induces TNF‐α and IL‐6 in an in vitro liver model and that macrophage‐derived TNF‐α mediates the induction of TNF‐α in hepatocytes.     

Proinflammatory and Anti‐Inflammatory Cytokines in Gingival Crevicular Fluid and Serum of Patients With Rheumatoid Arthritis and Patients With Chronic Periodontitis

Background: The aim of this study is to evaluate proinflammatory and anti‐inflammatory cytokine levels in gingival crevicular fluid (GCF) and serum of rheumatoid arthritis (RA) and chronic periodontitis (CP) patients to assess whether cytokine profiles distinguish patients with RA and patients with CP while using healthy patients as background controls. Methods: A total of 49 patients, 17 patients with RA (three males and 14 females; mean age: 47.82 ± 10.74 years), 16 patients with CP (10 males and six females; mean age: 44.00 ± 7.00 years), and 16 controls (eight males and eight females; mean age: 28.06 ± 6.18 years) were enrolled. Patients with RA were under the supervision of rheumatologists; 15 of the patients with RA were being treated with methotrexate–sulfasalazine combined therapy, and two of the patients were being treated with leflunomid therapy. Periodontal parameters (plaque index, gingival index, probing depth, and clinical attachment level) were recorded. Interleukin (IL)‐1β, IL‐4, IL‐10, and tumor necrosis factor‐α (TNF‐α) were determined in GCF and IL‐1β and IL‐10 in serum by enzyme‐linked immunosorbent assay. Results: There were significant differences found among RA, CP, and control groups for all periodontal parameters (P <0.05). The total amount and concentration of GCF IL‐1 β, IL‐4, IL‐10, and TNF‐α were similar in RA and CP patients (P >0.05). Although the total amount and concentration of serum IL‐10 was not significantly different among the groups (P >0.05), serum IL‐1β was significantly lower in the RA group compared to CP patients and controls and was higher in GCF of the RA group compared to the CP group. Conclusions: Although clinical periodontal disease parameters indicated more severe periodontal disease in CP compared to RA patients, immunologic evaluation did not reveal consistent results regarding proinflammatory and anti‐inflammatory cytokine levels. This might be a result of the use of non‐steroidal anti‐inflammatory drugs and rheumatoid agents by patients with RA.     

Xylitol,an Anticaries Agent,Exhibits Potent Inhibition of Inflammatory Responses in Human THP‐1‐Derived Macrophages Infected With Porphyromonas gingivalis

Background: Xylitol is a well‐known anticaries agent and has been used for the prevention and treatment of dental caries. In this study, the anti‐inflammatory effects of xylitol are evaluated for possible use in the prevention and treatment of periodontal infections. Methods: Cytokine expression was stimulated in THP‐1 (human monocyte cell line)‐derived macrophages by live Porphyromonas gingivalis, and enzyme‐linked immunosorbent assay and a commercial multiplex assay kit were used to determine the effects of xylitol on live P. gingivalis–induced production of cytokine. The effects of xylitol on phagocytosis and the production of nitric oxide were determined using phagocytosis assay, viable cell count, and Griess reagent. The effects of xylitol on P. gingivalis adhesion were determined by immunostaining, and costimulatory molecule expression was examined by flow cytometry. Results: Live P. gingivalis infection increased the production of representative proinflammatory cytokines, such as tumor necrosis factor‐α and interleukin (IL)‐1β, in a multiplicity of infection– and time‐dependent manner. Live P. gingivalis also enhanced the release of cytokines and chemokines, such as IL‐12 p40, eotaxin, interferon γ–induced protein 10, monocyte chemotactic protein‐1, and macrophage inflammatory protein‐1. The pretreatment of xylitol significantly inhibited the P. gingivalis–induced cytokines production and nitric oxide production. In addition, xylitol inhibited the attachment of live P. gingivalis on THP‐1‐derived macrophages. Furthermore, xylitol exerted antiphagocytic activity against both Escherichia coli and P. gingivalis. Conclusion: These findings suggest that xylitol acts as an anti‐inflammatory agent in THP‐1‐derived macrophages infected with live P. gingivalis, which supports its use in periodontitis.     

Cytokine profile in the gingival crevicular fluid of rheumatoid arthritis patients with chronic periodontitis

The aim was to assess the cytokine profile in the gingival crevicular fluid (GCF) of rheumatoid arthritis (RA) patients with chronic periodontitis (CP). Databases were searched from 1991 to August 2013 using a combination of various keywords. Eight studies were included. The GCF concentrations of interleukin (IL)‐1β, IL‐4, IL‐10, matrix metalloproteinase (MMP)‐8, MMP‐13 and tumor necrosis factor‐alpha (TNF‐α) were reported to be higher in patients with RA than in healthy controls (HC) without CP. In one study, TNF‐α levels in GCF were significantly higher in HC than in RA patients receiving anti‐TNF‐α therapy. One study reported no significant difference in GCF TNF‐α levels among RA patients and HC regardless of anti‐TNF‐α therapy. One study reported no difference in IL‐1β and prostaglandin E₂ levels among RA patients and HC with CP. Raised levels of proinflammatory cytokines are exhibited in the GCF of RA patients with CP.     

The role of cytokines in a Porphyromonas gingivalis‐induced murine abscess model

Introduction: Porphyromonas gingivalis is an important periodontopathic bacterium that is strongly associated with periodontal disease and is part of human dental plaque. Periodontal disease results from the interaction of the host with bacterial products, and T‐cell‐derived cytokines remain critical in the immunoregulation of periodontal disease. Methods: The aim of this study was to examine the role of T helper type 1 [interleukin‐12p40 (IL‐12p40), interferon‐γ, tumour necrosis factor (TNF)] and type 2 (IL‐4, IL‐10) cytokines in the immune response to a subcutaneous challenge with P. gingivalis using a well‐established murine abscess model, in genetically modified cytokine‐specific knockout mice. Results: IL‐12p40^−/− mice exhibited more advanced tissue destruction and a reduced inflammatory cell infiltrate after subcutaneous P. gingivalis challenge. Deficiency of IL‐4 or IL‐10 did not result in increased susceptibility to P. gingivalis‐mediated tissue destruction. Furthermore, TNF deficiency appeared to reduce local tissue destruction. Interestingly, serum‐specific antibodies suggested a strong T helper type 2 response. Conclusion: The results of our study indicate an important role for IL‐12 in a primary P. gingivalis subcutaneous challenge.     

A Sialidase‐Deficient Porphyromonas gingivalis Mutant Strain Induces Less Interleukin‐1β and Tumor Necrosis Factor‐α in Epi4 Cells Than W83 Strain Through Regulation of c‐Jun N‐Terminal Kinase Pathway

Background: Porphyromonas gingivalis is one of the major periodontal pathogens. In a previous study, a mouse abscess model showed that sialidase deficiency of P. gingivalis weakened its virulence, but the mechanism behind this observation remains unknown. Methods: A sialidase‐deficient mutant strain (△PG0352) and a complemented strain (com△PG0352) were constructed. Epi4 cells were stimulated by wild‐type strain P. gingivalis W83, △PG0352, or com△PG0352. Real‐time polymerase chain reaction was carried out to detect expression of virulent genes in P. gingivalis and interleukin (IL)‐1β, IL‐6, IL‐8, and tumor necrosis factor (TNF)‐α in epi4 cells. Activities of sialidase, gingipains, and lipopolysaccharide (LPS) were compared among the different P. gingivalis strains. Levels of IL‐1β and TNF‐α in the epi4 cells supernatant were detected by enzyme‐linked immunosorbent assay and levels of p38, extracellular signal‐regulated kinase, c‐Jun N‐terminal kinase (JNK), and phospho‐c‐Jun were detected by western blotting. Results: Compared with P. gingivalis W83 and com△PG0352, activities of Kgp and Rgp gingipains and amount of LPS decreased in △PG0352, whereas there were no differences in LPS activity among these three strains. Level of phospho‐JNK was lower in epi4 cells stimulated by △PG0352. △pG0352 induced less IL‐1β and TNF‐α and more IL‐8 in epi4 cells; differences in IL‐1β and TNF‐α could not be detected after JNK blocking. Conclusion: A sialidase‐deficient P. gingivalis mutant strain induces less IL‐1β and TNF‐α in epi4 cells than W83 strain through regulation of JNK pathway.     

Whole‐Blood Cultures From Patients With Chronic Periodontitis Respond Differently to Porphyromonas gingivalis but not Escherichia coli Lipopolysaccharide

Background: Porphyromonas gingivalis lipid A heterogeneity modulates cytokine expression in human cells. This study investigates the effects of two lipid A isoforms of P. gingivalis, lipopolysaccharide (LPS)_1435/1449 and LPS₁₆₉₀, on the secretion of proinflammatory and regulatory cytokines in total blood cultures from patients with and without chronic periodontitis (CP). Methods: A cross‐sectional study was conducted in 38 systemically healthy individuals divided in two groups: 1) the CP group (n = 19), in which patients were diagnosed with CP; and 2) the no periodontitis (NP) group (n = 19), which included control patients without CP. Blood samples were collected from all patients, and whole‐blood cell cultures (WBCCs) were stimulated for 48 hours with P. gingivalis LPS_1435/1449 and LPS₁₆₉₀ and Escherichia coli LPS. Unstimulated WBCCs served as negative controls. The secretion of interferon‐γ (IFN‐γ), interleukin‐10 (IL‐10), and transforming growth factor‐β (TGF‐β) was detected in WBCC supernatants by enzyme‐linked immunosorbent assays. Results: E. coli LPS significantly increased the expression of all cytokines in WBCCs from both the NP and CP groups when compared to non‐stimulated cells (control treatment). P. gingivalis LPS preparations increased IFN‐γ levels in the CP group but not in the NP group when compared with controls (P <0.05). P. gingivalis LPS preparations also increased IL‐10 and TGF‐β levels in both CP and NP groups, but P. gingivalis LPS₁₆₉₀ showed a three‐fold increase on IL‐10 production in the NP group (P <0.05) when compared to P. gingivalis LPS_1435/144. Conclusions: These data demonstrate that WBCC cell populations obtained from healthy individuals and patients with CP may differ in the cytokine response to P. gingivalis but not E. coli LPS. This is consistent with the notion that CP alters the systemic WBCC response and that this can be detected by the different P. gingivalis LPS structures.     

Synergistic effects of lipopolysaccharides from periodontopathic bacteria on pro‐inflammatory cytokine production in an ex vivo whole blood model

Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia have been strongly associated with chronic periodontitis. This disease is characterized by an accumulation of inflammatory cells in periodontal tissue and subgingival sites. The secretion of high levels of inflammatory cytokines by those cells is believed to contribute to periodontal tissue destruction. The aim of this study was to investigate the inflammatory response of whole blood from periodontitis patients following challenges with whole cells of P. gingivalis, T. denticola, and T. forsythia or their lipopolysaccharides (LPS), individually and in combination. Whole blood collected from seven periodontitis patients was stimulated with whole cells or LPS and the production of interleukin (IL)‐1β, IL‐6, IL‐8, and tumor necrosis factor alpha (TNF‐α) were quantified by enzyme‐linked immunosorbent assays. The mono and mixed challenges with whole bacterial cells or LPS induced the secretion of high amounts of IL‐1β, IL‐6, IL‐8, and TNF‐α by the mixed leukocyte population from periodontitis patients. In addition, P. gingivalis LPS, T. denticola LPS, and T. forsythia LPS acted in synergy to induce high levels of IL‐1β and TNF‐α. This study suggests that P. gingivalis, T. denticola, and T. forsythia may contribute to the immunodestructive host response characteristic of periodontitis through synergistic effects of their LPS on the inflammatory response induced by a mixed population of leukocytes.     

Production of inflammatory cytokines by human gingival fibroblasts stimulated by cell‐surface preparations of Porphyromonas gingivalis

Porphyromonas gingivalis is a gram‐negative rod associated with the progression of human periodontal disease. Inflammatory cytokines are believed to be the major pathological mediators in periodontal diseases. We therefore investigated the productions of interleukin‐1β (IL‐1β), interleukin‐6 (IL‐6), interleukin‐8 (IL‐8), and tumor necrosis factor‐α (TNF‐α) in human gingival fibroblasts treated with lipopolysaccharide, polysaccharide and outer‐membrane proteins from P. gingivalis ATCC 53977. Outer‐membrane protein from P. gingivalis enhanced the production of IL‐6 and IL‐8 from the cells of periodontium in vitro as well as lipopolysaccharide did. The IL‐8 production activity of polysaccharide from P. gingivalis was higher than that of other cell‐surface components. The levels of IL‐6 and IL‐8 released from the P. gingivalis lipopolysaccharide‐treated human gingival fibroblasts were lower than those of the same cells treated with lipopolysaccharides from Actinobacillus actinomycetemcomitans or Escherichia coli. Rabbit antisera against either outer‐membrane protein or lipopolysaccharide inhibited the IL‐6 and IL‐8 production derived from human gingival fibroblasts stimulated sonicated supernatants from P. gingivalis. The present study suggests that, in addition to lipopolysaccharide, outer‐membrane protein and polysaccharide of P. gingivalis are also pathological mediators in periodontal diseases.     

Improved periodontal health and cardiovascular risk

Background: Previous studies have demonstrated variable effects on systemic inflammatory and immune responses following improved periodontal health. This study examined changes in serum levels of the inflammatory mediators IL‐1β, IL‐6, TNF‐α and sICAM‐1, and antibodies to Porphyromonas gingivalis, human heat shock protein (hHSP) 60 and P. gingivalis GroEL following improvement in periodontal health in high cardiovascular (CV) risk and low CV‐risk patients. Methods: Patients retrospectively selected from a longitudinal study, had undergone yearly periodontal examinations and peripheral blood collections. They had demonstrated a quantifiable improvement in periodontal health (>60% reduction in number of sites with probing depth ≥4 mm from the baseline visit) and could be classified as either high CV‐risk (≥6 classical risk factors, n = 13) or low CV‐risk (≤1 classical risk factor, n = 14). Serum levels of the cytokines and antibodies were measured using ELISA. Results: For sICAM‐1 and anti‐P. gingivalis GroEL and anti‐hHSP60 antibodies, most patients recorded decreased levels. Reductions in serum sICAM‐1 levels were more notable in low CV‐risk patients (p = 0.006); and reductions in levels of anti‐P. gingivalis GroEL and anti‐hHSP60 antibodies (p = 0.001 and 0.009 respectively) were more notable in high CV‐risk patients. Conclusions: This study found that subsequent to improved periodontal health, the anti‐HSP (HSP60 and GroEL) antibody response was reduced, particularly for high CV‐risk patients. sICAM‐1 levels were also lowered, more so for low CV‐risk patients.     

Aggressive and Chronic Periodontitis Correlate With Distinct Cellular Sources of Key Immunoregulatory Cytokines

Background: Chronic periodontitis (CP) and aggressive periodontitis (AP) are inflammatory diseases and the main cause of dental loss in adults. We aimed to investigate the expression of adhesion molecules and the source of proinflammatory and anti‐inflammatory cytokines in circulating mononuclear cells from patients with CP and AP. Methods: Peripheral blood mononuclear cells from healthy controls and CP or AP patients were collected. The expression of the cell adhesion molecules CD11a and CD11b, and the cellular sources of interleukin (IL)‐4, IL‐10, IL‐12, interferon‐γ, and tumor necrosis factor‐α by distinct subpopulations of circulating leukocytes were determined using flow cytometry. Results: The expression of CD11a, but not CD11b, was significantly higher within the CD4⁺ and CD8⁺ T cells in CP and AP than in healthy controls. The frequencies of tumor necrosis factor‐α–expressing CD4⁺ T cells and CD14⁺ cells were higher in AP and CP, compared to healthy controls, respectively. Moreover, the frequency of IL‐10 expressing CD14⁺ cells was higher in CP, but not AP, compared to healthy controls CD4⁺ T cells committed to IL‐4 production was higher in CP than in healthy controls. Conclusion: These results suggest the participation of CD11a in the pathogenesis of periodontal lesions and show distinct cellular sources of immunoregulatory cytokines in AP versus CP.     

Saliva and Serum Levels of B‐Cell Activating Factors and Tumor Necrosis Factor‐α in Patients With Periodontitis

Background: B‐lymphocytes play a central and critical role in the adaptive immune response against invading pathogens. This study evaluates saliva and serum levels of APRIL (a proliferation‐inducing ligand), B‐cell activating factor (BAFF), tumor necrosis factor‐α (TNF‐α), interleukin (IL)‐6, and IL‐10 in patients with chronic periodontitis (CP) or aggressive periodontitis (AgP) and periodontally healthy individuals. Methods: Twenty‐five patients with AgP, 20 patients with CP, and 20 periodontally healthy individuals were included. Smoking status was recorded, and all individuals were divided into non‐smokers and smokers. Saliva and serum samples were collected before clinical periodontal measurements. APRIL, BAFF, TNF‐α, IL‐6, and IL‐10 levels in serum and saliva samples were determined by enzyme‐linked immunosorbent assay. Statistical analysis was performed using multivariate analysis of variance and bivariate correlation. Results: Serum and saliva levels of TNF‐α, APRIL, BAFF, IL‐6, and IL‐10 were similar in CP and AgP groups. Serum levels of TNF‐α, APRIL, and BAFF and saliva levels of BAFF were significantly higher in periodontitis groups than healthy controls (P <0.05). Non‐smokers with CP or AgP had lower levels of saliva TNF‐α and APRIL and serum APRIL and IL‐6 than smokers with CP or AgP (P <0.05). Saliva APRIL and serum TNF‐α and IL‐6 levels were significantly higher in healthy smokers than healthy non‐smokers (P <0.05). Clinical periodontal parameters correlated positively with TNF‐family cytokines and negatively with IL‐10 (P <0.05). Conclusions: Within the limits of this study, it may be suggested that elevated salivary and serum TNF‐α, APRIL, and BAFF in patients with periodontitis may contribute to the dominance of B cells in periodontitis lesions. Moreover, higher levels in healthy smokers than non‐smoking counterparts may play a role in detrimental effects of smoking on periodontal tissues.     

Role of MyD88‐dependent and MyD88‐independent signaling in Porphyromonas gingivalis‐elicited macrophage foam cell formation

Clinical studies and experimental modeling identify a potential link between periodontal disease and periodontal pathogens such as Porphyromonas gingivalis and atherosclerosis and formation of macrophage foam cells. Toll‐like receptors and molecules governing their intracellular signaling pathways such as MyD88 play roles in atherosclerosis, as well as host response to P. gingivalis. The aim of this study was to define roles of MyD88 and TRIF during macrophage foam cell formation in response to P. gingivalis. In the presence of human low‐density lipoprotein (LDL) mouse bone‐marrow‐derived macrophages (BMφ) cultured with P. gingivalis responded with significant reduction in tumor necrosis factor‐α (TNF‐α) and interleukin‐6 (IL‐6). The BMφ stained strongly with oil red O, regardless of whether bacterial challenge occurred concurrent with or before LDL treatment. Heat‐killed P. gingivalis stimulated foam cell formation in a similar way to live bacteria. The BMφ from MyD88‐knockout and Lps2 mice revealed a significant role for MyD88, and a minor role for TRIF in P. gingivalis‐elicited foam cell formation. Porphyromonas gingivalis‐elicited TNF‐α and IL‐6 were affected by MyD88 ablation and to a lesser extent by TRIF status. These data indicate that LDL affects the TNF‐α and IL‐6 response of macrophages to P. gingivalis challenge and that MyD88 and TRIF play important roles in P. gingivalis‐elicited foam cell formation.     

Virulence Mechanism of Bacteria in Mixed Infection: Attenuation of Cytokine Levels and Evasion of Polymorphonuclear Leukocyte Phagocytosis

Background: The objective of the present study is to evaluate the effect of bacterial viability on the virulence of mixed infection. Methods: Expression of pro‐ and anti‐inflammatory cytokines (interleukin [IL]‐1β and IL‐10, respectively) was tested in vivo, following live versus heat‐killed infection (mono or mixed), using the mouse chamber model of infection. Ex vivo, phagocytosis of fluorescently labeled bacteria was tested in primary mouse polymorphonuclear leukocytes by flow cytometry. Results: In monoinfection, heat‐killed Porphyromonas gingivalis led to augmented levels of IL‐1β 2 hours postinfection, whereas IL‐10 levels remained unaffected. Phagocytosis of heat‐killed P. gingivalis was reduced compared with that of the live P. gingivalis, whereas phagocytosis of heat‐killed Fusobacterium nucleatum was augmented compared with that of live F. nucleatum. In mixed infection, both IL‐1β and IL‐10 levels were augmented 24 hours postinfection when the bacteria were heat‐killed. Although the phagocytosis pattern of F. nucleatum in the mixed infection remained similar to that upon monoinfection, phagocytosis of P. gingivalis was reduced following mixed infection. Conclusions: The inflammatory response to live mixed infection is attenuated with reduced phagocytosis, compared with that of heat‐killed mixed infection. The lower response to live mixed infection could stem from a mechanism enabling the bacteria to evade the host response, thereby increasing bacterial survival.     

Tumor Necrosis Factor‐α and Interleukin (IL)‐1β, IL‐6, and IL‐8 Impair In Vitro Migration and Induce Apoptosis of Gingival Fibroblasts and Epithelial Cells,Delaying Wound Healing

Background: Multiple factors affect oral mucosal healing, such as the persistence of an inflammatory reaction. The present study evaluates effects of tumor necrosis factor (TNF)‐α and interleukin (IL)‐1β, IL‐6, and IL‐8 on epithelial cells (ECs) and human gingival fibroblasts (GFs) in vitro. Methods: GFs and ECs were seeded in 96‐well plates (1 × 10⁴ cells/well) in plain culture medium (Dulbecco’s modified Eagle’s medium [DMEM]) containing 1% antibiotic/antimycotic solution and 10% fetal bovine serum, and incubated for 24 hours. Both cell lines were exposed for 24 hours to the following cytokines: 1) TNF‐α (100 ng/mL); 2) IL‐1β (1 ng/mL); 3) IL‐6 (10 ng/mL); and 4) IL‐8 (10 ng/mL). All cytokines were diluted in serum‐free DMEM. Control cultures were exposed only to serum‐free DMEM. Effects of exposure to inflammatory cytokines were determined by means of: 1) apoptosis (anexin V); 2) cell migration (wound healing assay); 3) inflammatory cytokine synthesis (enzyme‐linked immunosorbent assay). Data were analyzed by Kruskal–Wallis and Mann–Whitney U tests (α = 0.05). Results: Increased apoptosis rates were noted when cells were exposed to inflammatory cytokines, except ECs exposed to IL‐1β. Cell migration was negatively affected by all inflammatory cytokines for both cell lines. ECs and GFs exposed to IL‐6 and IL‐8 significantly increased synthesis of TNF‐α and IL‐1β. Conclusions: Demonstrated results indicate negative effects of tested inflammatory cytokines on ECs and GFs, inducing apoptosis and impairing cell migration. These results can justify delayed oral mucosa healing in the presence of inflammatory reaction.     

Peripheral Blood Mononuclear Phagocytes From Patients With Chronic Periodontitis Are Primed for Osteoclast Formation

Background: During inflammatory periodontal disease, peripheral blood mononuclear cells (PBMCs) are attracted to bone and differentiate into active bone‐resorbing osteoclasts (OCs), thus providing evidence that the impact of chronic periodontitis (CP) on the activity of circulating mononuclear cells is of central importance. The authors test the hypothesis that peripheral blood mononuclear phagocytes (PBMPs) from patients with CP are activated and more susceptible to differentiation into OCs, which in turn would lead to more intense bone resorption. Methods: In vitro cytokine production by both unstimulated and lipopolysaccharide‐stimulated PBMCs from individuals with (n = 10) or without (n = 12) periodontitis was determined by cytokine array. OC differentiation from CD14⁺ PBMCs was induced by receptor activator of nuclear factor‐kappa B ligand (RANKL), either alone or in the presence of macrophage colony‐stimulating factor (M‐CSF). PBMC differentiation to OCs was confirmed by tartrate‐resistant acid phosphatase staining; bone resorbing activity was assessed by using an osteologic plate assay (bone resorption pit formation). Results: PBMCs from patients with CP produced tumor necrosis factor‐α and higher amounts of interferon‐γ, interleukin (IL)‐1α, IL‐1β, IL‐1rα, CXC motif chemokine 10, macrophage migration inhibitory factor, macrophage inflammatory protein (MIP)‐1α, and MIP‐1β than the control cells. OC differentiation was induced by RANKL alone in PBMCs from patients with CP, but not in PBMCs from the healthy controls, which required the addition of M‐CSF. In addition, PBMC‐derived OCs from patients with CP showed significantly higher resorption activity than that observed in the healthy controls. Also, the circulating concentrations of M‐CSF were significantly higher in patients with CP than in the control participants. Conclusions: These data indicate that in patients with CP, circulating PBMCs are primed for increased proinflammatory activity and that M‐CSF plays a central role in this process by increasing OC formation and the consequent bone resorption activity.