The in vivo expression of membrane-bound CD14 in periodontal health and disease

Macrophage-related gingival transcriptomic patterns and microbiome alterations in experimental periodontitis in nonhuman primates

OBJECTIVE

This study examined the microbiome features specifically related to host macrophage polarization in health, initiation and progression of periodontitis, and in resolution samples using a nonhuman primate model of ligature-induced periodontitis.

BACKGROUND

The oral microbiome is a complex of bacterial phyla, genera, and species acquired early in life into the individual autochthonous oral ecology. The microbiome changes overtime in response to both intrinsic and extrinsic stressors, and transitions to a dysbiotic ecology at sites of periodontal lesions.

METHODS

Comparisons were made between the microbial and host features in young (≤7 years) and adult (≥12 years) cohorts of animals. Footprints of macrophage-related genes in the gingival tissues were evaluated using expression profiles including M0, M1, and M2 related genes.

RESULTS

Within the gingival tissues, similar macrophage-related gene patterns were observed with significant increases with disease initiation and continued elevation throughout disease in both age groups. Approximately, 70% of the taxa were similar in relative abundance between the two groups; however, the adults showed a large number of OTUs that were significantly altered compared with the younger animals. Developing a correlation map identified three major node levels of interactions that comprised approximately ⅓ of the Operational Taxonomic Units (OTUs) that dominated the microbiomes across the samples. Also noted was a much greater frequency of significant correlations of individual OTUs with the macrophage phenotype markers, compared with disease and resolution samples in both age groups, with a greater frequency in the younger group. Moreover, these correlations were assigned to differentially expressed genes representing M0, M1, and M2-related phenotypes. A cluster analyses across the macrophage-related transcriptome and the OTUs demonstrated multiple somewhat distinct bacterial consortia, incorporating both commensal and putative pathogens, linked to the gene responses that differed in health, disease, and resolution samples. Finally, there were minimal alterations in the OTUs in individual clusters with specific macrophage-related responses in the younger group, while in the adult samples substantial variations were noted with genes from all macrophage phenotypes.

CONCLUSIONS

The results confirmed important features that could reflect macrophage polarization in periodontal lesions, and provided some initial data supporting specific members of the oral microbiome feature prominently related to specific gene response patterns consistent with macrophages in the gingival tissues.

Soluble LPS receptor CD14 is increased in saliva of patients with geographic tongue

OBJECTIVES

The soluble bacterial pattern recognition receptor, sCD14 augments inflammatory responses in oral cavity. The aim of the study was to investigate whether patients with geographic tongue (GT) with and without fissured tongue (FT) have impaired inflammatory regulation, manifesting as increased levels of sCD14 in the saliva.

MATERIAL AND METHODS

An enzyme-linked immunosorbent assay was used to measure the amount of sCD14 in whole and parotid saliva of patients diagnosed with GT (GT whole, n = 21; GT parotid, n = 23) and control subjects (GT whole, n = 25; GT parotid, n = 18). The levels of sCD14 were also evaluated according to our previous clinical assessment of GT based on the number of lesions detected on the tongue, as 'mild' (a single lesion), 'moderate' (2-5 lesions), or 'severe' (≥6 lesions). Diagnosis of FT was established when multiple grooves or fissures were observed on the dorsal and lateral surfaces of the tongue.

RESULTS

GT patients had significantly higher sCD14 levels in whole (p<.05) and parotid saliva (p<.001), compared with controls. GT patients with FT had significantly increased sCD14 levels only in parotid saliva. A gradual increase in sCD14 levels in parotid and unstimulated saliva was seen in GT patients with multiple tongue lesions compared with single lesions.

CONCLUSIONS

GT patients had increased sCD14 in both parotid and unstimulated saliva. sCD14 seems to increase local inflammatory responses, which suggests its involvement in the pathophysiology of GT.

The subversion of toll-like receptor signaling by bacterial and viral proteases during the development of infectious diseases

Toll-like receptors (TLRs) are pattern recognition receptors (PRRs) that respond to pathogen-associated molecular patterns (PAMPs). The recognition of specific microbial ligands by TLRs triggers an innate immune response and also promotes adaptive immunity, which is necessary for the efficient elimination of invading pathogens. Successful pathogens have therefore evolved strategies to subvert and/or manipulate TLR signaling. Both the impairment and uncontrolled activation of TLR signaling can harm the host, causing tissue destruction and allowing pathogens to proliferate, thus favoring disease progression. In this context, microbial proteases are key virulence factors that modify components of the TLR signaling pathway. In this review, we discuss the role of bacterial and viral proteases in the manipulation of TLR signaling, highlighting the importance of these enzymes during the development of infectious diseases.

Oral Dysbiosis and Autoimmunity: From Local Periodontal Responses to an Imbalanced Systemic Immunity. A Review

The current paradigm of onset and progression of periodontitis includes oral dysbiosis directed by inflammophilic bacteria, leading to altered resolution of inflammation and lack of regulation of the inflammatory responses. In the construction of explanatory models of the etiopathogenesis of periodontal disease, autoimmune mechanisms were among the first to be explored and historically, for more than five decades, they have been described in an isolated manner as part of the tissue damage process observed in periodontitis, however direct participation of these mechanisms in the tissue damage is still controversial. Autoimmunity is affected by genetic and environmental factors, leading to an imbalance between the effector and regulatory responses, mostly associated with failed resolution mechanisms. However, dysbiosis/infection and chronic inflammation could trigger autoimmunity by several mechanisms including bystander activation, dysregulation of toll-like receptors, amplification of autoimmunity by cytokines, epitope spreading, autoantigens complementarity, autoantigens overproduction, microbial translocation, molecular mimicry, superantigens, and activation or inhibition of receptors related to autoimmunity by microorganisms. Even though autoreactivity in periodontitis is biologically plausible, the associated mechanisms could be related to non-pathologic responses which could even explain non-recognized physiological functions. In this review we shall discuss from a descriptive point of view, the autoimmune mechanisms related to periodontitis physio-pathogenesis and the participation of oral dysbiosis on local periodontal autoimmune responses as well as on different systemic inflammatory diseases.

Estimation of soluble CD14 levels in gingival crevicular fluid and serum in diseased and healthy periodontium

OBJECTIVE

To estimate the levels of sCD14 in gingival crevicular fluid and serum under periodontally-healthy and diseased conditions.

METHODS

The subjects were divided into three groups of 15, each as follows: healthy, gingivitis, and periodontitis. Periodontal parameters including Probing pocket depth, Clinical attachment level, Bleeding index, and Plaque index. Gingival crevicular fluid and serum samples were collected and analyzed for sCD14 levels using commercially-available ELISA kits.

RESULTS

The mean concentration of sCD14 in GCF was significantly lower in the gingivitis (134.5 ± 26.85 ng/mL) and periodontitis (103.23 ± 20.36 ng/mL) groups than in the healthy group (172.77 ± 46.33 ng/mL); p < 0.001. The mean serum concentration of sCD14 in the healthy group was 1528.13 ± 387.37 ng/mL, which was significantly less than that of the periodontitis group (2051.50 ± 381.10 ng/mL); p = 0.011.

CONCLUSIONS

The serum sCD14 levels in the periodontitis groups were significantly higher than those in the healthy controls. The levels of sCD14 in GCF were significantly lower in the gingivitis and periodontitis groups than in the healthy group.

Differential profiles of soluble and cellular toll like receptor (TLR)-2 and 4 in chronic periodontitis

Chronic periodontitis is a common inflammatory disease initiated by a complex microbial biofilm and mediated by the host response causing destruction of the supporting tissues of the teeth. Host recognition of pathogens is mediated by toll-like receptors (TLRs) that bind conserved molecular patterns shared by large groups of microorganisms. The oral epithelial cells respond to most periodontopathic bacteria via TLR-2 and TLR-4. In addition to the membrane-associated receptors, soluble forms of TLR-2 (sTLR-2) and TLR-4 (sTLR-4) have been identified and are thought to play a regulatory role by binding microbial ligands. sTLR-2 has been shown to arise from ectodomain shedding of the extracellular domain of the membrane receptor and sTLR-4 is thought to be an alternate spliced form. Many studies have previously reported the presence of elevated numbers of viable exfoliated epithelial cells in the saliva of patients with chronic periodontitis. The objective of this study was to investigate the potential value of salivary sTLR-2 and sTLR-4 together with the paired epithelial cell-associated TLR-2/4 mRNA as diagnostic markers for chronic periodontitis. Unstimulated whole saliva was collected after obtaining informed consent from 40 individuals with either periodontitis or gingivitis. The sTLR-2 and sTLR4 in saliva was measured by enzyme-linked immunosorbent assay. The TLR-2 and TLR-4 transcript in the epithelial cells in saliva was measured by real time polymerase chain reaction. While levels of sTLR-2 exhibited an inverse correlation, sTLR-4 positively correlated with clinical parameters in the gingivitis cohort. Interestingly, both correlations were lost in the periodontitis cohort indicating a dysregulated host response. On the other hand, while the sTLR-2 and the paired epithelial cell associated TLR-2 mRNA exhibited a direct correlation (r2 = 0.62), that of sTLR4 and TLR-4 mRNA exhibited an inverse correlation (r2 = 0.53) in the periodontitis cohort. Collectively, assessments of salivary sTLR2 and sTLR4 together with the respective transcripts in the epithelial cells could provide clinically relevant markers of disease progression from gingivitis to periodontitis.

Salivary sCD14 as a potential biomarker of dental caries activity in adults

CD14 is a co-receptor involved in the recognition of Gram-negative and Gram-positive bacteria, the latter known to cause dental caries. The aim of this study was to determine whether soluble CD14 (sCD14) in saliva was associated with caries activity and the collection method from the saliva. The study included 55 participants aged 20 to 40 years, 30 with dental caries and 25 caries-free controls. We collected 110 saliva samples in total, 55 of resting saliva and 55 of mechanically stimulated saliva. Median levels of sCD14, measured with a matrix-matched enzyme-linked immunosorbent assay (ELISA), were higher in the caries-active than in the caries-free group in either resting (203.3 vs.167.9 ng mL-1; P<0.01) or stimulated saliva (201 vs.105.7 ng mL-1; P<0.01). The resting salivary flow rate was lower in the caries-active than caries-free group (0.61±0.42 vs. 0.98±0.52 mL min-1; P<0.01). Hyposalivation was observed only in the caries-active group (10 and 13 % in stimulated and resting saliva, respectively). Higher salivary sCD14 levels and secretion rates were clearly associated with dental caries and resting saliva. Future studies should focus on the clinical utility of salivary sCD14 as a potential biomarker and predictor of future caries events.

Porphyromonas gingivalis gingipains cause defective macrophage migration towards apoptotic cells and inhibit phagocytosis of primary apoptotic neutrophils

Periodontal disease is a prevalent chronic inflammatory condition characterised by an aberrant host response to a pathogenic plaque biofilm resulting in local tissue damage and frustrated healing that can result in tooth loss. Cysteine proteases (gingipains) from the key periodontal pathogen Porphyromonas gingivalis have been implicated in periodontal disease pathogenesis by inhibiting inflammation resolution and are linked with systemic chronic inflammatory conditions such as rheumatoid arthritis. Efficient clearance of apoptotic cells is essential for the resolution of inflammation and tissue restoration. Here we sought to characterise the innate immune clearance of apoptotic cells and its modulation by gingipains. We examined the capacity of gingipain-treated macrophages to migrate towards and phagocytose apoptotic cells. Lysine gingipain treatment of macrophages impaired macrophage migration towards apoptotic neutrophils. Furthermore, lysine gingipain treatment reduced surface expression levels of CD14, a key macrophage receptor for apoptotic cells, which resulted in reduced macrophage interactions with apoptotic cells. Additionally, while apoptotic cells and their derived secretome were shown to inhibit TNF-α-induced expression by P. gingivalis lipopolysaccharide, we demonstrated that gingipain preparations induced a rapid inflammatory response in macrophages that was resistant to the anti-inflammatory effects of apoptotic cells or their secretome. Taken together, these data indicate that P. gingivalis may promote the chronic inflammation seen in periodontal disease patients by multiple mechanisms, including rapid, potent gingipain-mediated inflammation, coupled with receptor cleavage leading to defective clearance of apoptotic cells and reduced anti-inflammatory responses. Thus, gingipains represent a potential therapeutic target for intervention in the management of chronic periodontal disease.

Periodontal CD14 mRNA expression is downregulated in patients with chronic periodontitis and type 2 diabetes

Background

Patients with type 2 diabetes mellitus (T2DM) have increased severity of periodontitis. Toll-like receptor (TLR)4, its co-receptors CD14 and MD-2, and adaptor MyD88 play pivotal roles in lipopolysaccharide (LPS)-triggered tissue inflammation and periodontitis. This study investigated the effects of T2DM and periodontitis on TLR4, CD14, MD-2 and MyD88 mRNA expression in surgically removed periodontal tissues.

Methods

Periodontal tissue specimens were collected from 14 patients without periodontitis and T2DM (Group 1), 15 patients with periodontitis alone (Group 2), and 7 patients with both periodontitis and T2DM (Group 3). The mRNA of TLR4, CD14, MD-2 and MyD88 was quantified using real-time PCR and compared between the groups.

Results

Statistical analysis showed that periodontal expression of CD14 mRNA was significantly reduced across Groups 1, 2 and 3 (p = 0.02) whereas the mRNA expression of TLR4, MD-2 and MyD88 was not significantly different among the groups. Furthermore, when patients in Groups 1 and 2 were combined (n = 22), the CD14 mRNA expression was significantly lower than that in patients of Group 1 (p = 0.04).

Conclusions

CD14 mRNA expression was downregulated across patients with neither periodontitis nor T2DM, patients with periodontitis alone and patients with both diseases, suggesting that CD14 mRNA expression is associated with a favorable host response or subjected to a negative feedback regulation.

Porphyromonas gingivalis gingipains selectively reduce CD14 expression, leading to macrophage hyporesponsiveness to bacterial infection

Cysteine proteases (gingipains) from Porphyromonas gingivalis are key virulence factors in chronic periodontitis. Innate immune receptors CD14, Toll-like receptor (TLR) 2 and TLR4 are important in P. gingivalis recognition. We examined the ability of gingipains to cleave CD14, TLR2 and TLR4, and the consequences for the cellular response to bacterial challenge. Macrophages were exposed to Arg (RgpA and RgpB)- and Lys (Kgp)-gingipains, and residual expression of TLR2, TLR4 and CD14 was determined by flow cytometry. The cellular response to live bacteria following exposure to purified gingipains was evaluated by TNFα production and bacterial phagocytosis. RgpA and Kgp decreased CD14 detection in a concentration (p = 0.0000002)- and time (p = 0.03)-dependent manner, whereas RgpB had no significant effect. TLR2 and TLR4 expression were unaffected. Reduction in CD14 expression was more efficient with Lys-gingipain than with Arg-gingipain. A reduced CD14 surface level correlated with decreased TNFα secretion and bacterial phagocytosis following challenge with live P. gingivalis, but the response to heat-killed bacteria was unaffected. Therefore, gingipains reduce CD14 expression without affecting expression of the bacterial-sensing TLRs. Reduced CD14 expression depends on the gingipain hemagglutinin/adhesion site and results in macrophage hyporesponsiveness to bacterial challenge. Further studies are needed to determine if reduced CD14 expression is linked to periodontitis induced by P. gingivalis.

Associations between CD14 -159 C>T polymorphism and chronic/aggressive periodontitis susceptibility

OBJECTIVES

CD14 is a causative gene for periodontitis. However, conflicting results had been achieved when evaluating the associations between CD14 -159 C>T and periodontitis, which warranted us to conduct this meta-analysis.

MATERIAL AND METHODS

A meta-analysis based on eight relevant case-control studies was conducted to address this issue. Odds ratios (OR) with 95% confidence intervals (CIs) were applied to test the association. The statistical heterogeneity across studies was assessed by Chi-square-based Q-test.

RESULTS

Retrieved studies regarding CD14 -159 C>T and periodontitis susceptibility were put into the final analysis. Overall and subgroup analyses were performed. Finally, we did not find that this polymorphism could contribute to modified risk of periodontitis or in stratified analysis by ethnicity and type of disease. However, this polymorphism was associated with decreased risk of mild to moderate periodontitis (TT vs. CC, OR = 0.42, 95% CI = 0.21-0.81, CT/CC vs. TT, OR = 1.91, 95% CI = 1.09-3.35) but not severe periodontitis.

CONCLUSION

The present meta-analysis provided confirmative evidence that CD14 -159 C>T was involved in the development of periodontitis.

Single nucleotide polymorphisms of pattern recognition receptors and chronic periodontitis

BACKGROUND AND OBJECTIVE

Periodontitis is a multifactorial disease influenced partly by genetics. Activation of pattern recognition receptors (PRRs) can lead to the up-regulation of inflammatory pathways, resulting in periodontal tissue destruction. Hence, functional polymorphisms located in PRRs can explain differences in host susceptibility to periodontitis. This study investigated single nucleotide polymorphisms of PRRs including toll-like receptor (TLR)2 (G2408A), TLR4 (A896G), TLR9 (T1486C), TLR9 (T1237C) and CD14 (C260T) in patients with chronic periodontitis and in periodontally healthy subjects.

METHODS

One-hundred and fourteen patients with chronic periodontitis and 77 periodontally healthy subjects were genotyped using TaqMan® allelic discrimination assays. Fisher's exact test and chi-square analyses were performed to compare genotype and allele frequencies.

RESULTS

The frequency of subjects with the CC genotype of CD14 (C260T) (24.6% in the chronic periodontitis group vs. 13% in the periodontally healthy group) and those expressing the T allele of CD14 (C260T) (CT and TT) (75.4% in the chronic periodontitis group vs. 87% in the periodontally healthy group) was statistically different among groups (p = 0.04). Homozygocity for the C allele of the CD14 (C260T) polymorphism (CC) was associated with a two--fold increased susceptibility to periodontitis (p = 0.04; odds ratio, 2.49; 95% confidence interval, 1.06-6.26). Individuals with the CC genotype of TLR9 (T1486C) (14.9% in the chronic periodontitis group vs. 28.6% in the periodontally healthy group) and those expressing the T allele of TLR9 (T1486C) (CT and TT) (85.1% in the chronic periodontitis group vs. 71.4% in the periodontally healthy group) were also significantly differently distributed between groups without adjustment (p = 0.03). Further analysis of nonsmokers revealed a significant difference in the distribution of genotypes between groups for TLR9 (T1486C; p = 0.017) and CD14 (C260T; p = 0.03), polymorphisms again without adjustment.

CONCLUSION

The CC genotype of CD14 (C260T) is related to susceptibility to chronic periodontitis in Caucasians. In addition, differences observed in the distribution of TLR9 (T1486C) genotypes between groups warrant further investigation.

Human gingiva is another site of C-reactive protein formation

OBJECTIVES

C-reactive protein (CRP) is primarily synthesized in the liver. It is hypothesized that human gingiva per se may produce CRP and its expression could be associated with IL-6. This study elucidated the CRP expression profile in human gingiva and its possible association with IL-6.

MATERIALS AND METHODS

Ninety-four gingival biopsies were collected from 44 subjects with chronic periodontitis and 18 periodontally healthy subjects. CRP protein was detected by immunohistochemistry and Western blotting, while CRP and IL-6 mRNAs were examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and real-time PCR. CRP protein expression in the reconstituted human gingival epithelia (RHGE) was examined by the particle-enhanced immunoturbidimetric assay and Western blotting.

RESULTS

CRP protein was detected in gingival tissues from patients and healthy subjects by immunohistochemistry and confirmed by Western blotting. Its expression pattern and level at 16 pairs of periodontal pocket tissues and the adjacent clinically healthy tissues from 16 patients were significantly interrelated (r(s)=0.693, p<0.01). CRP mRNA expression was strongly correlated with IL-6 (r=0.694, p<0.001). Both CRP protein and mRNA were detected in the RHGE.

CONCLUSIONS

The present study shows for the first time that human gingiva is able to produce CRP in situ that may be associated with IL-6 activity.

The oral microbial consortium's interaction with the periodontal innate defense system

The oral microbial consortium is the most characterized polymicrobial microbial community associated with the human host. Extensive sampling of both microbial and tissue samples has demonstrated that there is a strong association between the type of microbial community found in the gingival crevice and the status of innate host mediator expression. The strong clinical association between the microbial community and the innate host response in both clinically healthy and diseased tissue suggests that the oral consortium has a direct effect on periodontal tissue expression of innate defense mediators. A preliminary study in germ-free mice has demonstrated that the oral commensal consortium has direct effect on IL-1beta expression, indicating that this microbial community may contribute to the strong protective status of healthy gingival tissue. Likewise, the lipopolysaccharide composition and invasion characteristics of Porphyromonas gingivalis, an oral bacterium strongly associated with periodontitis, suggest that it may be a keystone member of the oral microbial community and facilitate a destructive change in the protective gingival innate host status.

Impact of genetic variants of CD14 and TLR4 on subgingival periodontopathogens

CD14 and toll-like receptor 4 (TLR4) are involved in host's immune response to bacterial pathogens including periodontal bacteria. Functional important gene polymorphisms are described for both genes. The aim of this study was to evaluate links between genetic polymorphisms of CD14 and TLR4 and risk markers of periodontitis in a multivariate model. One hundred and thirty-three periodontitis patients (chronic: n = 60, aggressive: n = 73) and 80 healthy controls without periodontitis were included in the study. Polymorphisms in CD14 c.-159C>T and in TLR4 Asp299Gly, Thr399Ile were determined by restriction fragment length polymorphism analyses. The clinical investigation included smoking status, plaque and bleeding indexes, pocket depth and attachment loss. Subgingival bacterial colonization was analysed molecularbiologically using the micro-Ident test. Prevotella intermedia occurred less frequently in individuals positive for the TT genotype of CD14 in bivariate analysis (odds ratio = 0.36%, confidence interval: 0.14-0.91, P = 0.045). In binary logistic regression analyses, the occurrence of this bacterium was significantly decreased in TT carriers (odds ratio = 0.31%, confidence interval: 0.81-0.12, P = 0.017) considering age, smoking and maximum clinical attachment loss at microbial test site as confounding factors. However, no significant association with chronic and or aggressive periodontitis and polymorphisms in CD14 and TLR4 could be proven. Although the CD14 c.-159C>T polymorphism could be shown to be associated with subgingival colonization with P. intermedia, there is no evidence that CD14 and TLR4 polymorphisms investigated are independent risk factors for chronic or aggressive periodontitis in German periodontitis patients.

Down-regulation of epidermal growth factor receptor-dependent signaling by Porphyromonas gingivalis lipopolysaccharide in life-expanded human gingival fibroblasts

BACKGROUND AND OBJECTIVE

Human gingival fibroblasts exhibit proliferative responses following epidermal growth factor exposure, which are thought to enhance periodontal regeneration in the absence of bacterial products such as lipopolysacharide. However, lipopolysaccharide challenge activates human gingival fibroblasts to release several inflammatory mediators that contribute to the immune response associated with periodontitis and attenuate wound repair. We tested the hypothesis that Porphyromonas gingivalis lipopolysaccharide-activated signaling pathways down-regulate epidermal growth factor receptor-dependent events.

MATERIAL AND METHODS

To study lipopolysaccharide/epidermal growth factor interactions in human gingival fibroblasts, we introduced the catalytic subunit of human telomerase into human gingival fibroblasts, thereby generating a more long-lived cellular model. These cells were characterized and evaluated for lipopolysaccharide/epidermal growth factor responsiveness and regulation of epidermal growth factor-dependent pathways.

RESULTS

Comparison of human telomerase-transduced gingival fibroblasts with human gingival fibroblasts revealed that both cell lines exhibit a spindle-like morphology and express similar levels of epidermal growth factor receptor, CD14 and Toll-like receptors 2 and 4. Importantly, human telomerase-transduced gingival fibroblasts proliferation rates are increased 5-9 fold over human gingival fibroblasts and exhibit a longer life span in culture. In addition, human telomerase-transduced gingival fibroblasts and human gingival fibroblasts exhibit comparable profiles of mitogen-activated protein kinase kinase (extracellular signal-regulated kinase 1/2) activation upon epidermal growth factor or P. gingivalis lipopolysaccharide administration. Interestingly, treatment with P. gingivalis lipopolysaccharide leads to a down-regulation of epidermal growth factor-dependent extracellular signal-regulated kinase 1/2, p38 and cyclic-AMP response element binding protein phosphorylation in both cell types.

CONCLUSION

These studies demonstrate that human telomerase-transduced gingival fibroblasts exhibit an extended life span and recapitulate human gingival fibroblasts biology. Moreover, this system has allowed for the first demonstration of lipopolysaccharide down-regulation of epidermal growth factor activated pathways in human gingival fibroblasts and should facilitate the analysis of signaling events relevant to the pathogenesis and treatment of periodontitis.

The expression profile of lipopolysaccharide-binding protein, membrane-bound CD14, and toll-like receptors 2 and 4 in chronic periodontitis

BACKGROUND

This study aimed to investigate the interrelationship of in vivo expression of lipopolysaccharide-binding protein (LBP) and membrane-bound CD14 (mCD14) in human gingival tissues as well as the coexpression of Toll-like receptors (TLR) 2 and 4 in association with periodontal conditions.

METHODS

Gingival biopsies were collected from 43 subjects with chronic periodontitis, including periodontal pocket tissues (PoTs) and clinically healthy gingival tissues (HT-Ps), and from 15 periodontally healthy subjects as controls (HT-Cs). The expression of LBP, CD14, TLR 2, and TLR 4 was detected by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

LBP and mCD14 peptides were simultaneously detected in 91% of PoTs, 85% of HT-Ps, and 100% of HT-Cs. LBP and mCD14 mRNAs were simultaneously detected in 55% of PoTs, 55% of HT-Ps, and 75% of HT-Cs. The expression of LBP was confined to the gingival epithelium, whereas mCD14 was observed around the epithelium-connective tissue interface. A positive correlation existed between LBP and mCD14 peptides in both detection expression (r(s) = 0.608; P <0.001) and expression levels (r = 0.304; P <0.05) of these two molecules. In PoTs, TLR 2 was detected in both pocket epithelia and macrophage-like cells in connective tissues, whereas TLR 4 was predominantly detected in connective tissues. In HT-Ps and HT-Cs, a weak expression of TLR 2 was found in gingival epithelia, and no TLR 4 expression was detected. In PoTs, mCD14 was codetected on CD68-labeled macrophages in the underlying connective tissues of pocket epithelium as well as on CD1a-labeled dendritic cells in the pocket epithelium and connective tissues interface. No similar expression profile was detected in HT-Ps and HT-Cs.

CONCLUSIONS

This study suggests that the in vivo expression of LBP and mCD14 may be interrelated. Altered cellular expression profiles of mCD14 and TLR 2 and 4 in periodontal pocket tissues imply that these pattern recognition receptors may play a role in periodontal pathogenesis.

Lipopolysaccharide-binding protein down-regulates the expression of interleukin-6 by human gingival fibroblast

BACKGROUND

Lipopolysaccharide-binding protein (LBP) participates in the interaction of lipopolysacchaide (LPS) with CD14 to modulate the expression of cytokines. Human gingival fibroblast may actively participate in LPS-induced immuno-inflammatory responses through CD14, toll-like receptor (TLR) superfamily, MD-2 and related adaptive proteins, leading to the expression of cytokines.

OBJECTIVES

The present in vitro study aimed to investigate the possible effect of LBP and E. coli LPS interaction on the expression of cellular LPS receptors and IL-6 by human gingival fibroblast.

METHODS

The mRNA expression of CD14, LBP, TLR-2, TLR-4, MD-2 and IL-6 in human gingival fibroblast explants was detected by reverse transcriptionpolymerase chain reaction (RT-PCR) in the presence or absence of E. coli LPS and recombinant human LBP (rhLBP), while IL-6 peptides were analyzed by ELISA and immunohistochemistry, respectively.

RESULTS

Human gingival fibroblast could constitutively express CD14, MD-2 and IL-6 mRNAs, but not TLR-2, TLR-4 and LBP mRNAs. E. coli LPS induced the messages expression of MD-2, TLR-2 and -4. The expression of both IL-6 message and peptide was up-regulated by E. coli LPS in a dose dependent manner. Whereas rhLBP could significantly down-regulate the expression of both mRNAs and peptides of CD14 and IL-6 but not MD-2 signals in the presence or absence of E. coli LPS. The up-regulated expression of TLR-2 and -4 by E. coli LPS no longer existed in the presence of rhLBP.

CONCLUSIONS

This study suggests that LBP may down-regulate the expression of IL-6 by human gingival fibroblast. Further studies are warranted to clarify the molecular mechanisms of LBP in regulation of cytokine expression by host cells and to elaborate the relevant clinical implications.

Time to abandon dogma: CD14 is expressed by non‐myeloid lineage cells

CD14 is a pattern recognition receptor; its important role in innate immunity is reviewed here. Since its discovery and subsequent classification at the first leucocyte typing workshop in 1982, CD14 has been thought of as a leucocyte differentiation antigen. However, it has become clear that CD14 is also expressed by many non-myeloid cells, and the evidence for this is presented. The possible role of the presence of low copy number CD14 on non-myeloid cells is discussed. It is time to acknowledge CD14 as an ubiquitous molecule and abandon the position that it is expressed by myeloid cells alone.