Rangsini Mahanonda

IL-8 and IDO Expression by Human Gingival Fibroblasts via TLRs

Human gingival fibroblasts (HGFs), a predominant cell type in tooth-supporting structure, are presently recognized for their active role in the innate immune response. They produce a variety of inflammatory cytokines in response to microbial components such as LPS from the key periodontal pathogen, Porphyromonas gingivalis. In this study, we demonstrated that HGFs expressed mRNA of TLRs 1, 2, 3, 4, 5, 6, and 9, but not TLRs 7, 8, and 10. Stimulation of HGFs with highly purified TLR2 ligand (P. gingivalis LPS), TLR3 ligand (poly(I:C)), TLR4 ligand (Escherichia coli LPS), and TLR5 ligand (Salmonella typhimurium flagellin) led to expression of IL-8 and IDO. A potent TLR 9 ligand, CpG oligodeoxynucleotide 2006 had no effect, although HGFs showed a detectable TLR9 mRNA expression. No significant enhancement on IL-8 or IDO expression was observed when HGFs were stimulated with various combinations of TLR ligands. Surprisingly, the TLR9 ligand CpG oligodeoxynucleotide 2006 was able to specifically inhibit poly(I:C)-induced IL-8 and IDO expression. TNF-α enhanced TLR ligand-induced IL-8 production in HGFs, whereas IFN-γ enhanced TLR ligand-induced IDO expression. HGF production of IDO in response to P. gingivalis LPS, IFN-γ, or the two in combination inhibited T cell proliferation in MLRs. The observed T cell inhibition could be reversed by addition of either 1-methyl-dl-tryptophan or l-tryptophan. Our results suggest an important role of HGFs not only in orchestrating the innate immune response, but also in dampening potentially harmful hyperactive inflammation in periodontal tissue.

Cigarette smoke extract modulates human β-defensin-2 and interleukin-8 expression in human gingival epithelial cells

BACKGROUND AND OBJECTIVE Human gingival epithelial cells (HGECs) are continually exposed to oral bacteria and to other harmful agents. Their responses to stimuli are critical in maintaining periodontal homeostasis. The aim of this study was to investigate the modulating effect of cigarette smoke extract (CSE) on the innate immune responses of HGECs. MATERIAL AND METHODS Toll-like receptor (TLR) expression of HGECs was determined by reverse transcriptase-polymerase chain reaction (RT-PCR). The effect of CSE or nicotine on the expression of the antimicrobial peptide human beta-defensin-2 (hBD-2) and the pro-inflammatory cytokine interleukin (IL)-8 in stimulated HGEC cultures was evaluated by RT-PCR and enzyme-linked immunosorbent assay. RESULTS The HGECs expressed mRNA of TLRs 1, 2, 3, 5, 6, 9, 10, and minimally of TLR4, but not of TLRs 7 or 8. Stimulation of HGECs with highly purified TLR2, 3 or 5 ligands led to expression of hBD-2 and of IL-8. Enhancement of hBD-2 and IL-8 was observed in HGECs after combined stimulation with Porphyromonas gingivalis lipopolysaccharide (TLR2 ligand) and tumour necrosis factor-alpha, compared with stimulation using either agent alone. After CSE exposure, hBD-2 expression was markedly reduced in stimulated HGEC cultures, whereas IL-8 expression was markedly increased. These effects were also observed, but were markedly attenuated, upon nicotine treatment. CONCLUSION Human gingival epithelial cells play a critical role in orchestrating the innate immune responses of periodontal tissue via TLR signalling. Our results represent the first demonstration that CSE can modulate HGEC function by suppressing hBD-2 and enhancing IL-8 production, and this may be, in part, a possible mechanism which promotes periodontal disease.

Effects of IL-17 on Human Gingival Fibroblasts

Interleukin (IL)-17 is present in inflammatory periodontal lesions, thus suggesting a role in mediating inflammation. We tested the hypothesis that IL-17, especially when combined with interferon (IFN)-γ, may modulate the responses of human gingival fibroblasts (HGFs). IL-17 induced IL-8 and minimal intercellular adhesion molecule (ICAM)-1 expression. It had no effect on expression of HLA-DR, CD40, or the immune-suppressive enzyme indoleamine 2,3-dioxygenase (IDO). The effects of IL-17 on HGFs were compared with those of IFN-γ. Unlike IL-17, IFN-γ augmented the expression of HLA-DR, ICAM-1, and IDO, but not IL-8. Thus, IL-17 and IFN-γ induce different HGF responses when administered separately. Interestingly, when IL-17 and IFN-γ were combined, marked enhancement of ICAM-1, IL-8, and IDO expression by HGFs was observed. These findings suggest that IL-17, especially when combined with IFN-γ, could play an important role in immune modulation through stimulation of HGFs in periodontal disease.

Antiviral immune responses in H5N1-infected human lung tissue and possible mechanisms underlying the hyperproduction of interferon-inducible protein IP-10.

Information on the immune response against H5N1 within the lung is lacking. Here we describe the sustained antiviral immune responses, as indicated by the expression of MxA protein and IFN-alpha mRNA, in autopsy lung tissue from an H5N1-infected patient. H5N1 infection of primary bronchial/tracheal epithelial cells and lung microvascular endothelial cells induced IP-10, and also up-regulated the retinoic acid-inducible gene-I (RIG-I). Down-regulation of RIG-I gene expression decreased IP-10 response. Co-culturing of H5N1-infected pulmonary cells with TNF-alpha led to synergistically enhanced production of IP-10. In the absence of viral infection, TNF-alpha and IFN-alpha also synergistically enhanced IP-10 response. Methylprednisolone showed only a partial inhibitory effect on this chemokine response. Our findings strongly suggest that both the H5N1 virus and the locally produced antiviral cytokines; IFN-alpha and TNF-alpha may have an important role in inducing IP-10 hyperresponse, leading to inflammatory damage in infected lung.

Tissue Distribution of Memory T and B Cells in Rhesus Monkeys following Influenza A Infection

Studies of influenza-specific immune responses in humans have largely assessed systemic responses involving serum Ab and peripheral blood T cell responses. However, recent evidence indicates that tissue-resident memory T (TRM) cells play an important role in local murine intrapulmonary immunity. Rhesus monkeys were pulmonary exposed to 2009 pandemic H1N1 virus at days 0 and 28 and immune responses in different tissue compartments were measured. All animals were asymptomatic postinfection. Although only minimal memory immune responses were detected in peripheral blood, a high frequency of influenza nucleoprotein–specific memory T cells was detected in the lung at the “contraction phase,” 49–58 d after second virus inoculation. A substantial proportion of lung nucleoprotein-specific memory CD8+ T cells expressed CD103 and CD69, phenotypic markers of TRM cells. Lung CD103+ and CD103- memory CD8+ T cells expressed similar levels of IFN-γ and IL-2. Unlike memory T cells, spontaneous Ab secreting cells and memory B cells specific to influenza hemagglutinin were primarily observed in the mediastinal lymph nodes. Little difference in systemic and local immune responses against influenza was observed between young adult (6–8 y) and old animals (18–28 y). Using a nonhuman primate model, we revealed substantial induction of local T and B cell responses following 2009 pandemic H1N1 infection. Our study identified a subset of influenza-specific lung memory T cells characterized as TRM cells in rhesus monkeys. The rhesus monkey model may be useful to explore the role of TRM cells in local tissue protective immunity after rechallenge and vaccination.

Human Memory B Cells in Healthy Gingiva, Gingivitis, and Periodontitis

The presence of inflammatory infiltrates with B cells, specifically plasma cells, is the hallmark of periodontitis lesions. The composition of these infiltrates in various stages of homeostasis and disease development is not well documented. Human tissue biopsies from sites with gingival health (n = 29), gingivitis (n = 8), and periodontitis (n = 21) as well as gingival tissue after treated periodontitis (n = 6) were obtained and analyzed for their composition of B cell subsets. Ag specificity, Ig secretion, and expression of receptor activator of NF-κB ligand and granzyme B were performed. Although most of the B cell subsets in healthy gingiva and gingivitis tissues were CD19+CD27+CD38− memory B cells, the major B cell component in periodontitis was CD19+CD27+CD38+CD138+HLA-DRlow plasma cells, not plasmablasts. Plasma cell aggregates were observed at the base of the periodontal pocket and scattered throughout the gingiva, especially apically toward the advancing front of the lesion. High expression of CXCL12, a proliferation-inducing ligand, B cell–activating factor, IL-10, IL-6, and IL-21 molecules involved in local B cell responses was detected in both gingivitis and periodontitis tissues. Periodontitis tissue plasma cells mainly secreted IgG specific to periodontal pathogens and also expressed receptor activator of NF-κB ligand, a bone resorption cytokine. Memory B cells resided in the connective tissue subjacent to the junctional epithelium in healthy gingiva. This suggested a role of memory B cells in maintaining periodontal homeostasis.

Infection of human gingival fibroblasts with Aggregatibacter actinomycetemcomitans: An in vitro study

OBJECTIVE Aggregatibacter actinomycetemcomitans is known to be a major cause of localized aggressive periodontitis. Previous research has suggested that A. actinomycetemcomitans can damage many types of host cells. There is evidence for the ability of this organism to invade endothelial and epithelial cells, but information pertaining to its potential for invading gingival fibroblasts is very limited. Internalization of bacteria is not only responsible for damaging host tissue but also a means to evade the host immune response. It was hypothesized that A. actinomycetemcomitans can invade and reside in human gingival fibroblasts (HGF). METHODS Primary cultures of HGF were infected with A. actinomycetemcomitans at a ratio of 1:100. Bacterial internalization was determined by an antibiotic protection assay. Bacterial-fibroblast interaction was examined using phase-contrast, scanning and transmission electron microscopy. RESULTS It was demonstrated that A. actinomycetemcomitans was internalized into HGF at an efficiency of 0.084%. Transmission electron microscopic study showed the presence of A. actinomycetemcomitans in the cytoplasm of HGF without the surrounding membrane. Scanning electron micrographs revealed the sloughing of HGF surfaces on which A. actinomycetemcomitans adhered. Rounded cells, attachment loss and damaged cells were also observed. CONCLUSIONS It is concluded that the attachment and invasion of A. actinomycetemcomitans into human gingival fibroblasts play a role in periodontal tissue damage and may also be a means of immune evasion.

Monocyte Activation by Porphyromonas gingivalis LPS in Aggressive Periodontitis with the Use of Whole-blood Cultures

In this study, we re-visited the issue of hyper-responsiveness of monocytes to bacterial lipopolysaccharide (LPS) in aggressive periodontitis patients. We used whole-blood cultures to compare monocyte activation by Porphyromonas gingivalis LPS between Thai subjects with generalized aggressive periodontitis and those without periodontitis. Upon stimulation with P. gingivalis LPS, expression of co-stimulatory molecules on monocytes and expression of CD69 on NK and γδ T-cells were analyzed by flow cytometry, and the production of interleukin-1β and prostaglandin E2 was monitored by ELISA. LPS stimulation resulted in a dose-dependent up-regulation of CD40, CD80, and CD86 on monocytes, and up-regulation of CD69 on NK cells and γδ T-cells in both the periodontitis and non-periodontitis groups. The levels of activation markers and the mediator production after LPS stimulation were quite similar for both groups. In conclusion, we did not observe hyper-responsiveness of monocytes to P. gingivalis LPS challenge in Thai patients with aggressive periodontitis.

Cross-reactive Antibodies against Avian Influenza Virus A (H5N1)

To the Editor: Intravenous immunoglobulin (IVIg) is used to treat bacterial and viral infections in patients with primary immunodeficiency disease and those with autoimmune and inflammatory disorders (1). IVIg contains pooled IgG from >1,000 blood donors and antibodies against various common human pathogens, including influenza virus A. We tested the efficacy of commercial preparations of IVIg (50 mg/mL of highly purified immunoglobulin) against homosubtypic influenza viruses A (H1N1 and H3N2) and their cross-reactivity against avian influenza virus A (H5N1). IVIg preparations (Octagam; Octapharma, Vienna, Austria and Flebogamma; Instituto Grifols, Barcelona, Spain) had hemagglutination inhibition (HI) titers against subtypes H1N1 and H3N2 ranging from 20 to 40. Human Immunoglobulin, pH 4.0, (Harbin Sequel Bio-Engineering Pharmaceutical, Harbin, People’s Republic of China) had lower HI titers against homosubtypic avian influenza viruses (10 for subtype H3N2 and <10 for subtype H1N1). As expected, we did not detect antibodies against hemagglutinin (HA) of subtype H5N1 (A/open-billed/stork/Nahkonsawan/BBD0104F/2004) in any of the IVIg preparations (HI titer <10). Human influenza subtype H1N1 shares the same neuraminidase (NA) subtype (human N1) as subtype H5N1 (avian N1). We therefore tested whether IVIg preparations would react and inhibit NA activity of human and avian influenza viruses by using a neuraminidase inhibition (NI) assay (2). NI titer was defined as the reciprocal of the highest dilution that gave 50% reduction compared with that of the virus control. All 3 IVIg preparations inhibited NA activity of human N1 (NI titer against subtype H1N1 range 258–986) and human N2 (NI titer against subtype H3N2 range 1,309–3,274). Enzyme activity of avian N1 (7:1 reassortant; PR8 + NA [A/Vietnam/DT-0361/2005 H5N1]) was inhibited by all IVIg preparations (NI titer range 143–231). These findings support the recent observation of neutralizing antibodies against human N1 in human serum, which could inhibit enzyme activity of avian N1 from subtype H5N1 (3,4). We also tested IVIg preparations against reverse genetics subtype H5N3 virus in which the N3 NA was derived from H2N3 virus (6:1:1 reassortant; 6 internal genes from PR8 + HA (A/Vietnam/DT-0361/05 H5N1) + NA (A/duck/Germany 1207 H2N3) and observed no effect (NI titer <10). The N3 subtype belongs to avian influenza NA. Thus, antibodies against NA in IVIg appear to be specific for those circulating human influenza viruses (human N1 and human N2). Unlike HA and NA, virus matrix 2 ectodomain (M2e) is highly conserved. Its presence on the surface of the viral particle makes it a potential target of antibody response similar to that for HA and NA (5,6). We assessed reactivity of IVIg preparations against a consensus M2e peptide derived from human influenza viruses of H1, H2, and H3 subtypes (MSLLTEVETPIRNEWGCRCNDSSD) and those derived from A/Hong Kong/156/97 H5N1 (MSLLTEVETLTRNGWGCRCSDSSD and A/Thailand/ SP-83/2004 H5N1 (MSLLTEVETPTRNEWECRCSDSSD) by using ELISA (7). Antibody titer was defined as the reciprocal of the highest dilution that had an optical density of 0.5 at 414 nm in our assay. Results showed considerable variation among IVIg preparations, caused by M2e peptides derived from different influenza viruses (titer range 88–23,614). Among the 3 preparations, Human Immunoglobulin, pH 4.0, IVIg showed the highest titers against all M2e peptides (consensus, 9,639; H5N1 Hong Kong, 3,519; and H5N1 Thailand, 23,614). Variation of antibody titers against M2e in IVIGs may be geographically dependent. Unlike Octagam and Flebogamma, Human Immunoglobulin, pH 4.0, IVIg was likely derived from blood donors in China. Octagam and Immunoglobulin, pH 4.0, IVIg were more reactive with M2e of avian influenza virus (H5N1) (A/Thailand/SP-83/2004) than with other M2e peptides. We measured the ability of IVIg preparations to inhibit influenza subtype H5N1 replication by using a plaque-reduction assay. Subtype H5N1 (A/open-billed stork/ Nakhonsawan/BBD0104F/2004) was maintained as described (8). MDCK cells were infected with virus and agar containing various concentrations of IVIg was layered on top of these cells and incubated for 2 days. Results are shown in the Figure. IVIG inhibited plaque formation in a dose-dependent manner. Although plaques of heterogeneous size were observed in infected plates without IVIg, larger plaques were preferentially neutralized with increasing concentrations of IVIg in the agar (Figure). Figure Neutralization of avian influenza virus A (H5N1) by intravenous immunoglobulin (IVIg) preparations measured by percentage reduction in plaque number (A) and plaque size (B). Monolayers of MDCK cells were infected with virus and overlaid with agar containing ... Premixing excess M2e peptide with IVIg to absorb M2e-specific antibodies had no effect on plaque formation, indicating that antibodies against M2e in IVIg preparations were not responsible for neutralization of influenza subtype H5N1. Antibodies against M2e may have a role in protection against subtype H5N1 by another mechanism. Our data suggest that the neutralizing activity against influenza subtype H5N1 in all 3 IVIg preparations was likely contributed by cross-reactive antibodies against avian N1. IVIg has been reported to have antiinflammatory activity (9,10). The immune suppressive effect of IVIg may benefit patients by reducing the cytokine storm. These data suggest use of IVIg, especially preparations containing high neutralizing activity against subtype H5N1, as adjunctive treatment for infection with highly pathogenic avian influenza virus (H5N1).

MxA expression induced by α‐defensin in healthy human periodontal tissue

Although periodontal tissue is continually challenged by microbial plaque, it is generally maintained in a healthy state. To understand the basis for this, we investigated innate antiviral immunity in human periodontal tissue. The expression of mRNA encoding different antiviral proteins, myxovirus resistance A (MxA), protein kinase R (PKR), oligoadenylate synthetase (OAS), and secretory leukocyte protease inhibitor (SLPI) were detected in both healthy tissue and that with periodontitis. Immunostaining data consistently showed higher MxA protein expression in the epithelial layer of healthy gingiva as compared with tissue with periodontitis. Human MxA is thought to be induced by type I and III interferons (IFNs) but neither cytokine type was detected in healthy periodontal tissues. Treatment in vitro of primary human gingival epithelial cells (HGECs) with α‐defensins, but not with the antimicrobial peptides β‐defensins or LL‐37, led to MxA protein expression. α‐defensin was also detected in healthy periodontal tissue. In addition, MxA in α‐defensin‐treated HGECs was associated with protection against avian influenza H5N1 infection and silencing of the MxA gene using MxA‐targeted‐siRNA abolished this antiviral activity. To our knowledge, this is the first study to uncover a novel pathway of human MxA induction, which is initiated by an endogenous antimicrobial peptide, namely α‐defensin. This pathway may play an important role in the first line of antiviral defense in periodontal tissue.