Apoptosis and antigen receptor function in T and B cells following exposure to herpes simplex virus

T cells are an essential component of the immune response against herpes simplex virus (HSV) infection. We previously reported that incubation of T cells with HSV-infected fibroblasts inhibits subsequent T cell antigen receptor signal transduction. In the current study, we found that incubation of T cells with HSV-infected fibroblasts also leads to apoptosis in exposed T cells. Apoptosis was observed in Jurkat cells, a T cell leukemia line, and also in CD4(+) cells isolated from human peripheral blood mononuclear cells. Direct infection of these cells with HSV also resulted in apoptosis. Clinical isolates of both HSV type 1 and 2 induced apoptosis in infected T cells at comparable levels to cells infected with laboratory strains of HSV, suggesting an immune evasion mechanism that may be clinically relevant. Further understanding of these viral immune evasion mechanisms could be exploited for better management of HSV infection.     

Bacterial antigens induce collagenase and prostaglandin E2 synthesis in human gingival fibroblasts through a primary effect on circulating mononuclear cells.

Our previous work suggests that one mechanism through which connective tissue breakdown might occur in periodontal diseases is the production of metalloproteinases, including collagenase, by gingival fibroblasts. In this study we investigated whether highly purified preparations of lipopolysaccharide (LPS) and lipoteichoic acid (LTA) from a number of putative periodontal pathogens could induce monolayer cultures of human gingival fibroblasts to synthesize collagenase and prostaglandin E2. Using both biochemical assays and immunocytochemical techniques, we found that cells synthesized only very small amounts of collagenase in direct response to LPS or LTA (0.1 to 20.0 micrograms/ml). At the highest dose of both antigens, prostaglandin E2 production was increased. We then studied whether LPS and LTA could signal collagenase production by interacting primarily with a different cell type. Our results show that LPS and LTA were each able to stimulate cultures of human blood mononuclear cells (greater than 95% monocytes) to release collagenase-inducing cytokines. By indirect immunocytochemistry, we found that a large proportion of human gingival fibroblasts was activated to produce collagenase by supernatants from LPS- and LTA-stimulated mononuclear cells, whereas gingival fibroblasts cultured with supernatants from unstimulated mononuclear cells were not. Furthermore, in a population of activated fibroblasts we demonstrated, using a double-labeling technique, that some cells made collagenase and the specific tissue inhibitor of metalloproteinases (TIMP) simultaneously. As yet, the collagenase-inducing signals remain poorly characterized but the interleukins-1 and tumor necrosis factors seem likely candidates.     

CD40 engagement modulates the production of matrix metalloproteinases by gingival fibroblasts

Chronic periodontitis is a destructive inflammatory disease linked with unbalanced production between matrix metalloproteinases (MMPs), such as interstitial collagenase (MMP-1) and stromelysin-1 (MMP-3) and their endogenous tissue inhibitors of MMPs (TIMPs). In addition to aberrant MMP-1 and MMP-3 expression, periodontal lesions are characterized by dense infiltrations of activated T lymphocytes which may interact with CD40-expressing gingival fibroblasts in the connective tissue via the CD40L-CD40 pathway. In this study we investigated whether CD40 cross-linking influenced MMP production by gingival fibroblasts. Therefore, we analysed the CD40L-induced MMP production by these fibroblasts in the presence of cytokines that are increased in periodontal lesions, such as IL-1β, tumour necrosis factor-alpha (TNF-α) and interferon-gamma (IFN-γ). We show that CD40 ligation on gingival fibroblasts resulted in a decrease of their MMP-1 and MMP-3 production, while MMP-2 and TIMP-1 production were unaffected as determined by Western blot. This down-regulatory effect of CD40 engagement on MMP-1 and MMP-3 production by gingival fibroblasts was also present when MMP production was up-regulated by IL-1β and TNF-α or down-regulated by IFN-γ. These results suggest that CD40 ligation on gingival fibroblasts leads to a restraining of MMP-1 and MMP-3 production by gingival fibroblasts and thereby may be an important mechanism in the retardation of further periodontal tissue damage.     

Immunopathological activities of extracellular products of Streptococcus mitis, particularly a superantigenic fraction.

Previously, we prepared extracellular products, fractions F-1 and F-2 of Streptococcus mitis 108, an isolate from the tooth surface of an infant, and showed that F-1 exhibited inflammatory cytokine-inducing activities. In the present study, we present evidence that fraction F-2 induced human T-cell proliferation in the presence of irradiated human peripheral blood mononuclear cells and selectively activated T cells bearing V beta 2 and V beta 5.1 in the T-cell receptor. F-1, on the other hand, stimulated human gingival fibroblasts to support the T-cell proliferation in the same way as human gamma interferon or Prevotella intermedia lipopolysaccharide (LPS). Fraction F-1 also primed gingival fibroblasts to support the production of interleukin-2 and gamma interferon by the T cells upon stimulation with F-2. Human gingival fibroblasts stimulated with fraction F-1, like those stimulated by P. intermedia LPS and human gamma interferon, exhibited human leukocyte antigen (HLA)-DR mRNA expression and cell surface HLA-DR molecules as detected by enzyme-linked immunosorbent assay. An anti-HLA-DR monoclonal antibody inhibited T-cell proliferation in response to F-2, probably through inactivating the accessory function of HLA-DR-bearing fibroblasts. T cells activated with F-2 in the presence of irradiated peripheral blood mononuclear cells exhibited definite cytotoxic effects against fibroblasts and squamous carcinoma cells originating from human oral tissues. These findings are strongly suggestive of an association of extracellular products of viridans streptococci with pathogenesis of oral mucosal diseases, particularly those disorders in gingiva which are accompanied by heavy infiltration of T cells.     

Spontaneous production of thymocyte-activating factor by human gingival fibroblasts and its autoregulatory effect on their proliferation.

The purpose of this study was to examine whether human gingival fibroblasts produce a cytokine which modulates in immune and inflammatory responses including alterations in connective tissue metabolism in periodontal tissue. We found that a cultured human gingival fibroblast cell line (Gin-1) and freshly isolated human gingival fibroblasts produced thymocyte-activating factor(s), so we called the factor(s) fibroblast-derived thymocyte-activating factor (FTAF). Growth of the producing cell was itself modulated by the factor(s). Gin-1 cells spontaneously produced a significant amount of FTAF in a cell growth-dependent manner. Maximum activity was observed in conditioned medium from stationary-phase cells. The activity in conditioned medium of cultures lacking serum was significantly higher than that in those containing serum. Treatment of Gin-1 cell cultures with cycloheximide, an inhibitor of protein synthesis, markedly inhibited FTAF production. When Gin-1 cells were stimulated by triggering with muramyl dipeptide or sonicated extracts of Bacteroides gingivalis, FTAF production was significantly stimulated. Freshly isolated human gingival fibroblasts from gingival biopsies of healthy donors also produced FTAF which enhanced thymocyte proliferation. Peaks of thymocyte proliferation activity in conditioned medium from Gin-1 cells were observed in fractions having molecular weights of 25,000, 35,000, and 45,000, as determined by Sephadex G-75 column chromatography. The peak fractions (partially purified FTAF) significantly suppressed the proliferation of Gin-1 cells themselves as evaluated by [3H]thymidine uptake. The suppressive effect of partially purified FTAF was, at least partially, mediated by endogenous prostaglandin for the following reasons: addition of indomethacin, and inhibitor of prostaglandin synthesis, abrogated the suppressive effect; partially purified FTAF stimulated the production of prostaglandin E2 by the cells; and the suppression of cell proliferation was reinforced by addition of exogenous prostaglandins. These observations suggest that gingival fibroblasts play a significant role in regulation of cell growth of lymphocytes and in their own growth under physiological conditions and in pathological states in periodontal connective tissue.     

PI3 kinase and direct S-nitrosation are involved in down-regulation of apoptosis signal-regulating kinase 1 during LPS-induced Toll-like receptor 4 signalling

Toll-like receptor 4 (TLR4) is the human pattern recognition receptor that detects lipopolysaccharide (LPS) shared by Gram-negative bacteria. TLR4 is expressed in different cell types including myeloid cells, the key effectors of innate immune reactions. Apoptosis signal-regulating kinase 1 (ASK1), the upstream kinase of MAP kinase-dependent apoptotic pathway has recently been found to be selectively required for p38 MAP kinase activation/cytokine production during TLR4 signalling. However, the activity of this enzyme has to be down-regulated to protect the cells against apoptosis. In the present study we have found that inhibition of PI3 kinase by LY294002 in THP-1 cells exposed to LPS attenuated down-regulation of ASK1 activity followed by programmed cell death. In addition, nitric oxide produced in response to exposure of THP-1 cells to LPS was found to S-nitrosate and therefore, down-regulate ASK1 activity.     

Lipopolysaccharides from Periodontopathic Bacteria Porphyromonas gingivalis and Capnocytophaga ochracea Are Antagonists for Human Toll-Like Receptor 4

Toll-like receptors (TLRs) 2 and 4 have recently been identified as possible signal transducers for various bacterial ligands. To investigate the roles of TLRs in the recognition of periodontopathic bacteria by the innate immune system, a Chinese hamster ovary (CHO) nuclear factor-kappaB (NF-kappaB)-dependent reporter cell line, 7.7, which is defective in both TLR2- and TLR4-dependent signaling pathways was transfected with human CD14 and TLRs. When the transfectants were exposed to freeze-dried periodontopathic bacteria, Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Capnocytophaga ochracea, and Fusobacterium nucleatum, and a non-oral bacterium, Escherichia coli, all species of the bacteria induced NF-kappaB-dependent CD25 expression in 7.7/huTLR2 cells. Although freeze-dried A. actinomycetemcomitans, F. nucleatum, and E. coli also induced CD25 expression in 7.7/huTLR4 cells, freeze-dried P. gingivalis did not. Similarly, lipopolysaccharides (LPS) extracted from A. actinomycetemcomitans, F. nucleatum, and E. coli induced CD25 expression in 7.7/huTLR4 cells, but LPS from P. gingivalis and C. ochracea did not. Furthermore, LPS from P. gingivalis and C. ochracea attenuated CD25 expression in 7.7/huTLR4 cells induced by repurified LPS from E. coli. LPS from P. gingivalis and C. ochracea also inhibited the secretion of interleukin-6 (IL-6) from U373 cells, the secretion of IL-1beta from human peripheral blood mononuclear cells, and ICAM-1 expression in human gingival fibroblasts induced by repurified LPS from E. coli. These findings indicated that LPS from P. gingivalis and C. ochracea worked as antagonists for human TLR4. The antagonistic activity of LPS from these periodontopathic bacteria may be associated with the etiology of periodontal diseases.     

Interactions between periodontal bacteria and human oral epithelial cells: Fusobacterium nucleatum adheres to and invades epithelial cells

Bacteria are causative agents of periodontal diseases. Interactions between oral bacteria and gingival epithelial cells are essential aspects of periodontal infections. Using an in vitro tissue culture model, a selected group of gram-negative anaerobic bacteria frequently associated with periodontal diseases, including Bacteroides forsythus, Campylobacter curvus, Eikenella corrodens, Fusobacterium nucleatum, Porphyromonas gingivalis, and Prevotella intermedia, were examined for their ability to adhere to and invade primary cultures of human gingival epithelial cells (HGEC). The effects of these bacteria on the production of interleukin-8 (IL-8), a proinflammatory chemokine, were also measured. These studies provided an initial demonstration that F. nucleatum adhered to and invaded HGEC and that this was accompanied by high levels of IL-8 secretion from the epithelial cells. The attachment and invasion characteristics of F. nucleatum were also tested using KB cells, an oral epithelial cell line. The invasion was verified by transmission electron microscopy and with metabolic inhibitors. Invasion appeared to occur via a "zipping" mechanism and required the involvement of actins, microtubules, signal transduction, protein synthesis, and energy metabolism of the epithelial cell, as well as protein synthesis by F. nucleatum. A spontaneous mutant, lam, of F. nucleatum, isolated as defective in autoagglutination, was unable to attach to or invade HGEC or KB cells, further indicating the requirement of bacterial components in these processes. Sugar inhibition assays indicated that lectin-like interactions were involved in the attachment of F. nucleatum to KB cells. Investigation of these new virulence phenotypes should improve our understanding of the role of F. nucleatum in periodontal infections.     

Role of cell-cell communication in inhibiting butyric acid-induced T-cell apoptosis

We have previously demonstrated that human gingival fibroblasts rescue butyric acid-induced T-cell apoptosis via proinflammatory cytokines such as interleukin 6 (IL-6) and IL-11, which are produced by fibroblasts stimulated with butyric acid. In this study, we determined if T-cell adhesion to human gingival fibroblasts influenced the susceptibility of T cells to butyric acid-induced apoptosis. We have shown that the number of Jurkat T cells adherent to gingival fibroblasts (Gin-1 cells) was significantly increased by the addition of butyric acid. All Jurkat cells that adhered to Gin-1 cells remained viable, while the nonadherent Jurkat cells dropped into apoptosis. The increase in T-cell adhesion to fibroblasts was also observed when Jurkat cells, but not Gin-1 cells, were pretreated with butyric acid. The expression levels of CD44, very late antigen 2 (VLA-2) and VLA-5 but not of leukocyte function-associated antigen 1 (LFA-1) and VLA-4 on Jurkat cells were increased following treatment with butyric acid. Furthermore, pretreatment of butyric acid-sensitized Jurkat cells with monoclonal antibodies against CD44, VLA-2, and VLA-5, but not LFA-1 and VLA-4, followed by coculture with Gin-1 cells inhibited T-cell adhesion to fibroblasts and increased apoptosis of nonadherent T cells after coculture of gingival fibroblasts and Jurkat cells. These results indicate that T-cell adherence to fibroblasts is enhanced by butyric acid and that butyric acid-induced T-cell apoptosis is down-regulated by T-cell adhesion to gingival fibroblasts through an interaction with the adhesion molecules CD44, VLA-2, and VLA-5 expressed on T cells stimulated with butyric acid.     

Identification of epithelial auto-antigens associated with periodontal disease

We previously reported evidence that patients with periodontitis have serum antibodies to oral Gram positive bacteria that are cross-reactive with epithelial antigens. In the present report cross-reactive epithelial antigens including CD24, lactate dehydrogenase A [LDM-A], antioxidant protein 2 [AOP 2] and nuclear factor of activated T cells 5 [NFAT 5], were identified by screening a cDNA expression library with pooled patient sera. Titres of antibodies to CD24 peptide correlated negatively with indices of periodontal disease severity. Strong expression of CD24 in the reactive periodontal epithelium and inflamed gingival attachment contrasted with low to undetectable expression in the external gingival epithelium. In periodontitis, a local action of these auto-reactive antibodies could modulate the regulatory potential associated with expression of CD24 in this epithelium.     

Effects of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) on the expression of inflammatory cytokines and apoptosis induction in rheumatoid synovial fibroblasts and monocytes.

This study was performed to investigate whether peroxisome proliterator-activated receptor-gamma (PPAR-gamma) exerted an anti-inflammatory effect on rheumatoid synovial cells and inhibited dysregulated proliferation. The expression of PPAR-gamma mRNA in cultured human synoviocytes and THP-1 cells was analysed by RT-PCR. PPAR-gamma was expressed in normal, osteoarthritis (OA), rheumatoid arthritis (RA) synovial cells as well as a human monocytic cell line, THP-1. In RA and OA synoviocytes, the induction of inflammatory cytokine mRNA expression such as TNF-alpha and IL-1beta was significantly inhibited by the natural PPAR-gamma agonist, 15 deoxy-Delta(12,14)prostaglandin J(2)(15d-PGJ(2)). The effect of PPAR-gamma on the nuclear factor (NF)-kappaB activity was tested by electrophoretic mobility shift assay (EMSA). Both troglitazone and 15d-PGJ(2)markedly inhibited TNF-alpha-induced NF-kappaB activation at 30 microM. However, PPAR-gamma agonist neither reduced proliferation nor induced apoptosis in RA synoviocytes when measured by XTT assay and fluorescence activated cell sorter (FACS) analysis. In contrast, it induced apoptosis in a dose-dependent manner in THP-1 cells and augmented TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis as well. In conclusion, these data demonstrate that PPAR-gamma is expressed in human synoviocytes and THP-1 cells, and the PPAR-gamma activation inhibits expression of inflammatory cytokines in RA synoviocytes. Furthermore, PPAR-gamma activation induces apoptosis by itself and augments TRAIL/Apo2L-induced apoptosis in THP-1 cells. These results suggest that PPAR-gamma agonists may provide a new therapeutic approach for RA.     

高糖对THP-1细胞及平滑肌细胞肿瘤坏死因子相关凋亡诱导配体受体4表达的影响

目的：探讨高糖对单核/巨噬细胞系THP-1细胞及人主动脉平滑肌细胞肿瘤坏死因子相关凋亡诱导配体受体4(TRAIL-R4)表达的影响。方法：用PMA孵育THP-1细胞，诱导其分化成为巨噬细胞。流式细胞仪检测成功诱导的巨噬细胞粘附分子CD11b及CD11c。采用不同糖浓度干预THP-1细胞，用Western blotting技术检测TRAIL-R4的表达。用25 mmol/L 高糖培养液在不同时点孵育人主动脉平滑肌细胞，观察TRAIL-R4蛋白表达的变化。用PKC激动剂干预THP-1细胞后，用Western blotting技术检测TRAIL-R4的表达。结果：佛波酯(PMA)孵育THP-1细胞48 h可诱导其分化成为巨噬细胞。20 mmol/L 高糖明显上调人THP-1细胞TRAIL-R4的表达。高糖对人主动脉平滑肌细胞TRAIL-R4表达上调的影响随着刺激时间的增加而增加。PKC激活后THP-1细胞TRAIL-R4的表达明显上调。结论：高糖上调TRAIL-R4蛋白表达，TRAIL-R4通过抑制巨噬细胞及平滑肌细胞的凋亡促进动脉粥样硬化。     

All-trans retinoic acid induces TLR-5 expression and cell differentiation and promotes flagellin-mediated cell functions in human THP-1 cells

Toll-like receptor 5 (TLR-5), which is expressed on macrophages and dendritic cells (DCs), is a crucial cell surface molecule that senses microbial-associated molecular patterns and initiates host innate immune responses upon infection with invaders that express flagellin. Little information is known about the induction factors and mechanisms of TLR-5 expression. In this study, we demonstrate that all-trans retinoic acid (ATRA) significantly up-regulated TLR-5 expression in human macrophage THP-1 cells by co-activating NF-κB and the RARα receptor and inducing the differentiation of CD11b(-)CD11c(-) THP-1 cells to CD11b(+)CD11c(low) cells. Furthermore, when stimulated with flagellin, ATRA-induced THP-1 cells expressed multiple cytokines, including TNF-α, IL-1beta, and IL-12p40, and several co-stimulatory molecules, such as CD40, CD80, CD86, and MHC class I and II. We also showed that when ATRA-induced THP-1 cells were stimulated with flagellin, the cells displayed an allostimulatory capacity rather than phagocytic activity. Taken together, our findings suggest that ATRA is a crucial immunostimulatory cofactor that induces the activation of macrophages and their subsequent differentiation into dendritic-like cells.     

Diminished forkhead box P3/CD25 double-positive T regulatory cells are associated with the increased nuclear factor-kappaB ligand (RANKL+) T cells in bone resorption lesion of periodontal disease

Periodontal disease involves multi-bacterial infections accompanied by inflammatory bone resorption lesions. The abundant T and B lymphocyte infiltrates are the major sources of the osteoclast differentiation factor, receptor activator for nuclear factor-kappaB ligand (RANKL) which, in turn, contributes to the development of bone resorption in periodontal disease. In the present study, we found that the concentrations of RANKL and regulatory T cell (T(reg))-associated cytokine, interleukin (IL)-10, in the periodontal tissue homogenates were correlated negatively, whereas RANKL and proinflammatory cytokine, IL-1beta, showed positive correlation. Also, according to the fluorescent-immunohistochemistry, the frequency of forkhead box P3 (FoxP3)/CD25 double-positive cells was diminished strikingly in the bone resorption lesion of periodontal disease compared to healthy gingival tissue, while CD25 or FoxP3 single positive cells were still observed in lesions where abundant RANKL+ lymphocytes were present. Very importantly, few or no expressions of FoxP3 by the RANKL+ lymphocytes were observed in the diseased periodontal tissues. Finally, IL-10 suppressed both soluble RANKL (sRANKL) and membrane RANKL (mRANKL) expression by peripheral blood mononuclear cells (PBMC) activated in vitro in a bacterial antigen-specific manner. Taken together, these results suggested that FoxP3/CD25 double-positive T(reg) cells may play a role in the down-regulation of RANKL expression by activated lymphocytes in periodontal diseased tissues. This leads to the conclusion that the phenomenon of diminished CD25+FoxP3+ T(reg) cells appears to be associated with the increased RANKL+ T cells in the bone resorption lesion of periodontal disease.