Leishmania expressed lipophosphoglycan interacts with Toll‐like receptor (TLR)‐2 to decrease TLR‐9 expression and reduce anti‐leishmanial responses

Two different Toll‐like receptors (TLRs) have been shown to play a role in host responses to Leishmania infection. TLR‐2 is involved in parasite survival in macrophages upon activation by lipophosphoglycan (LPG), a virulence factor expressed by Leishmania. In contrast, activation of TLR‐9 has been shown to promote a host‐protective response. However, whether there is a relationship between the interaction of LPG and TLR‐2, on one hand, with the effect of TLR‐9, on the other hand, remains unknown. In this study, we report that in‐vitro infection of macrophages with a L. major parasite with high expression levels of LPG results in decreased TLR‐9 expression compared to infection with a L. major parasite with lower expression levels of LPG. Addition of anti‐LPG as well as anti‐TLR‐2 antibodies prevents this reduction of TLR‐9 expression. Also, the addition of purified LPG to macrophages results in a decrease of TLR‐9 expression, which is shown to be mediated by transforming growth factor (TGF)‐β and interleukin (IL)‐10. Finally, in‐vitro treatment of macrophages with anti‐LPG and/or anti‐TLR‐2 antibodies before infection reduces the number of amastigotes in macrophages and co‐treatment of mice with anti‐TLR‐2 antibodies and cytosine–phosphate–guanosine (CpG) reduces footpad swelling and parasite load in the draining lymph nodes, accompanied by an interferon (IFN)‐γ‐predominant T cell response. Thus, for the first time, we show how interactions between LPG and TLR‐2 reduce anti‐leishmanial responses via cytokine‐mediated decrease of TLR‐9 expression.     

Activation profile of Toll‐like receptors of peripheral blood lymphocytes in patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease associated with aberrant activation of T and B lymphocytes for the production of inflammatory cytokines and autoreactive antibodies. Animal studies of SLE have indicated that Toll‐like receptors (TLR) are important in the pathogenesis of murine lupus. In the present clinical study, differential protein expressions of TLR‐1–9 of monocytes and different lymphocyte subsets from patients with SLE and normal control subjects were determined by flow cytometry. Results showed that the expression of intracellular TLRs (TLR‐3, ‐8, ‐9) and extracellular TLRs (TLR‐1, ‐2, ‐4, ‐5, ‐6) were elevated in monocytes, CD4⁺ T lymphocytes, CD8⁺ T lymphocytes and B lymphocytes of SLE patients compared to control subjects (all P < 0·001). Moreover, cell surface expression of TLR‐4 on CD4⁺ T lymphocytes and CD8⁺ T lymphocytes, and TLR‐6 on B lymphocytes, were correlated positively with SLE disease activity index (SLEDAI) (TLR‐4 on CD4⁺ T lymphocytes and CD8⁺ T lymphocytes: r = 0·536, P = 0·04; r = 0·713, P = 0·003; TLR‐6 in B lymphocytes: r = 0·572, P = 0·026). In concordance with the above results, there is an observable increased relative induction (%) of inflammatory cytokine interleukin (IL)‐1β, IL‐6, IL‐10 and IL‐12, chemokines CCL2, CXCL8, CCL5 and CXCL10 from peripheral blood mononuclear cells (PBMC) upon differential stimulation by PolyIC (TLR‐3 ligand), lipopolysaccharide (TLR‐4 ligand), peptidoglycan (TLR‐2 ligand), flagellin (TLR‐5 ligand), R837 (TLR‐7 ligand) and CpG DNA (TLR‐9 ligand) in SLE patients compared to controls. These results suggest that the innate immune response for extracellular pathogens and self‐originated DNA plays immunopathological roles via TLR activation in SLE.     

A live Leishmania major vaccine containing CpG motifs induces the de novo generation of Th17 cells in C57BL/6 mice

Cutaneous leishmaniasis produces open sores that lead to scarring and disfiguration. We have reported that vaccination of C57BL/6 mice with live Leishmania major plus CpG DNA (Lm/CpG) prevents lesion development and provides long‐term immunity. Our current study aims to characterize the components of the adaptive immune response that are unique to Lm/CpG. We find that this vaccine enhances the proliferation of CD4⁺ Th17 cells, which contrasts with the highly polarized Th1 response caused by L. major alone; the Th17 response is dependent upon release of vaccine‐induced IL‐6. Neutralization of IFN‐γ and, in particular, IL‐17 caused increased parasite burdens in Lm/CpG‐vaccinated mice. IL‐17R‐deficient Lm/CpG‐vaccinated mice develop lesions, and display decreased IL‐17 and IFN‐γ, despite normal IL‐12, production. Neutrophil accumulation is also decreased in the IL‐17R‐deficient Lm/CpG‐vaccinated mice but Treg numbers are augmented. Our data demonstrate that activation of immune cells through CpG DNA, in the presence of live L. major, causes the specific induction of Th17 cells, which enhances the development of a protective cellular immunity against the parasite. Our study also demonstrates that vaccines combining live pathogens with immunomodulatory molecules may strikingly modify the natural immune response to infection in an alternative manner to that induced by killed or subunit vaccines.     

A distinct Toll-like receptor repertoire in human tonsillar B cells, directly activated by PamCSK, R-837 and CpG-2006 stimulation

Toll‐like receptors (TLRs) recognize specific pathogen‐associated molecular patterns (PAMPs), which subsequently trigger innate immunity. Recent data also suggest a role for TLRs in the direct activation of adaptive immune cells. In the present study, the expression and function of TLR1–TLR10 were characterized in purified human tonsillar B cells, focusing on differences among CD19⁺ CD38^– CD27^– (naïve B cells), CD19⁺ IgD^– CD27^–[germinal centre (GC) B cells] and CD19⁺ CD38^– CD27⁺ (memory B cells) cells. The study was also designed to compare the TLR expression in B cells obtained from infected and hyperplastic tonsils that served as controls. The results demonstrated a distinct repertoire of TLRs, in which TLR1, TLR2, TLR7, TLR9 and TLR10 predominated. No differences were found among naïve, GC and memory B cells. Tonsillar infection did not substantially alter the TLR expression profile in ex vivo‐isolated B‐cell subsets. Purified CD19⁺ B cells stimulated with Pam₃CSK₄, R‐837 and CpG oligodeoxynucleotide (ODN) 2006, via TLR1/TLR2, TLR7 and TLR9, respectively, showed an induction of interleukin‐6 secretion and an up‐regulated expression of human leucocyte antigen (HLA)‐DR. Collectively, the present study demonstrates that B cells exhibit constitutively high levels of specific TLRs, which are not developmentally regulated during the B‐cell differentiation process. Ongoing microbial infections, such as chronic tonsillitis, do not appear to affect the TLR profile in B cells. Furthermore, the distinct expression of TLRs allows B cells to respond directly to the cognate PAMPs. This further emphasizes the role of TLRs in directly activating adaptive immune cells.     

Effective therapeutic anticancer vaccines based on precision guiding of cytolytic T lymphocytes

Summary: In natural immune responses CD4⁺ T helper (Th) cells, reactive with peptide antigens presented by major histocompatibility complex (MHC) class II molecules on dendritic cells (DC), can drive the maturation of DC that is required for induction of CD8⁺ cytolytic T‐lymphocyte (CTL) immunity. Proper induction, expansion and maintenance of CTL responses are achieved through delicate interactions between CD4⁺ T cells, DC and CD8⁺ T cells involving several ligand–receptor pairs. Th cells to a large extent operate through up‐regulation of CD40L, which then interacts with CD40 on DC to cause DC maturation. Subsequent CTL induction by activated DC requires CD80/CD86 on the DC to interact with the CD28 costimulatory receptor on CD8⁺ T cells. For maintenance and full expansion of CTL, interaction of the DC‐expressed 4–1BB ligand with its receptor 4–1BB on CTL is also important. Alternative molecular triggers of DC activation that can support induction of powerful CTL responses include agonistic anti‐CD40 antibody or ligands of Toll‐like receptors (TLR) such as LPS (TLR4 ligand) or oligodeoxynucleotides containing CpG‐motifs (TLR9 ligand). The combination of CpG adjuvant with a 35 amino acid long synthetic peptide comprising both tumor‐specific CTL and Th epitopes proved to be a highly effective vaccine formulation capable of inducing therapeutic immunity against human papillomavirus‐induced mouse tumors. The recently acquired insights into antigen presentation and costimulatory signals have made possible the development of a new generation of therapeutic anticancer vaccines.     

Participation of TLR2 and TLR4 in Cytokines Production by Patients with Symptomatic and Asymptomatic Chronic Chagas Disease

Chagas disease (CD), caused by the protozoan Trypanosoma cruzi, is a serious public health issue. Its evolution involves an acute stage, characterized by no specific symptoms, and the chronic stage during most individuals are asymptomatic, but about 30–40% of them become symptomatic presenting the cardiac or digestive disease. Host immune response mechanisms involved in symptomatic or asymptomatic chronic disease are not fully understood. The pro‐inflammatory cytokines are crucial in host resistance. However, a fine control of this inflammatory process, by action of anti‐inflammatory cytokines, is necessary to avoid tissue injury. This control was found to be responsible for no clinical manifestations in asymptomatic individuals. Toll‐like receptors (TLRs) are extremely important in defining the cytokine profile released in response to a micro‐organism. We found that patients with the cardiac form predominantly released the pro‐inflammatory cytokines: IFN‐γ, TNF‐α and IL‐17 with the involvement of both, TLR2 and TLR4. In contrast, patients with asymptomatic disease release predominantly the anti‐inflammatory cytokines IL‐10 and TGF‐β, but also with TLR2 and TLR4 participation. The mechanisms by which stimulation of the same TLRs results in release of different pattern of cytokines, depending on the patients group that is being evaluated, are discussed.     

Satellite glial cells in human trigeminal ganglia have a broad expression of functional Toll‐like receptors

Toll‐like receptors (TLRs) orchestrate immune responses to a wide variety of danger‐ and pathogen‐associated molecular patterns. Compared to the central nervous system (CNS), expression profile and function of TLRs in the human peripheral nervous system (PNS) are ill‐defined. We analyzed TLR expression of satellite glial cells (SGCs) and microglia, glial cells predominantly involved in local immune responses in ganglia of the human PNS and normal‐appearing white matter (NAWM) of the CNS, respectively. Ex vivo flow cytometry analysis of cell suspensions obtained from human cadaveric trigeminal ganglia (TG) and NAWM showed that both SGCs and microglia expressed TLR1–5, TLR7, and TLR9, although expression levels varied between these cell types. Immunohistochemistry confirmed expression of TLR1–TLR4 and TLR9 by SGCs in situ. Stimulation of TG‐ and NAWM‐derived cell suspensions with ligands of TLR1–TLR6, but not TLR7 and TLR9, induced interleukin 6 (IL‐6) secretion. We identified CD45^LOWCD14^POS SGCs and microglia, but not CD45^HIGH leukocytes and CD45^NEG cells as the main source of IL‐6 and TNF‐α upon stimulation with TLR3 and TLR5 ligands. In conclusion, human TG‐resident SGCs express a broad panel of functional TLRs, suggesting their role in initiating and orchestrating inflammation to pathogens in human sensory ganglia.     

Decreased functional response to Toll like receptor ligands in patients with oral cancer

Patients with oral cancer (OC) show dysregulation of variety of anti tumor immune responses. To assess the role of Toll like receptor (TLR) signaling in peripheral blood lymphocytes (PBL) from OC patients, we analyzed the expression of TLR2, TLR3, TLR4 and TLR9 on various lymphocyte subsets. Results revealed an increased expression of TLRs on unconventional T cells (like γδ T cells, NKT cells and CD4⁺CD8⁺ T cells) as compared to conventional αβ T cells. Functional studies using TLR ligands (CpG, Poly I:C, LPS and Pam3CSK4) showed defects in the TLR mediated signaling in PBLs of OC patients. Proliferation of OC PBLs in response to stimulation with TLR ligands was significantly decreased. TLR ligand induced IFN-γ production by PBLs from OC patients were low as compared to HI. Stimulation with TLR ligands upregulated the levels of activation markers (CD25 and CD69) on PBLs from HI but not from OC patients. TLR ligands CpG, Poly I:C, LPS and Pam3CSK4 significantly augmented the tumor directed cytotoxic response of PBLs from HI but not from OC patients. Our data suggests that impairment of TLR function on PBLs may be another strategy adopted by tumor cells to dampen tumor directed immune responses.     

Human polymorphonuclear leukocytes produce cytokines in response to Leishmania major promastigotes

Polymorphonuclear leukocytes (PMN) release cytokines that may influence the development of the subsequent adaptive immune response. Little is known about cytokines produced by human PMN in response to Leishmania (L.). In this study, mRNA expression of Interleukin (IL)‐12p40, IL‐12p35, Interferon (IFN)‐γ, transforming growth factor (TGF)‐β, IL‐1, and IL‐4 in PMN of volunteers stimulated with L. major promastigotes has been investigated by real‐time PCR and the results were confirmed by flow cytometer. The results showed that L. major did not induce mRNA expression of IL12p40, IL12p35, IFN‐γ, and TGF‐β in PMN, while IL‐1 and IL‐4 mRNA were induced. Flow cytometry results confirmed no IFN‐γ production by PMN with or without stimulation. IL‐12p70 was present in untreated and L. major‐treated PMN, and these cells release IL‐12 following incubation with L. major. Significant amount of IL‐1 even without treatment with promastigotes was detected in PMN. Moreover, the proportion of PMN, which produce IL‐1 in response to L. major, was increased compared with the percent of unstimulated IL‐1‐producing PMN. The results showed the accumulation of small amounts of IL‐4 in PMN after stimulation. In conclusion, our results indicate that IL‐12 and IL‐1 are pre‐stored in human PMN, nor L. major induces IL‐1 and IL‐4, but not IL‐12, IFN‐γ, nor TGF‐β expression in these cells.     

CD27+ B cells from a subgroup of common variable immunodeficiency patients are less sensitive to apoptosis rescue regardless of interleukin‐21 signalling

Common variable immunodeficiency (CVID) is a primary immunodeficiency characterized by hypogammaglobulinaemia and recurrent infections. Although the underlying cause is unknown, B cells from most CVID patients fail to differentiate to memory or plasma cells. We investigated if increased apoptosis could influence the fate of B cells. For this purpose we activated purified B lymphocytes of CVID patients with a surrogate T‐dependent (anti‐CD40) or T‐independent [cytosine–phosphate–guanosine oligodeoxynucleotides (CpG‐ODN) or anti‐immunoglobulin (Ig)M)] stimulus with or without interleukin (IL)‐21. We found that CD27⁺ B cells were more sensitive than CD27^– B cells to spontaneous apoptosis and less sensitive to rescue from apoptosis. The addition of IL‐21 down‐modulated the protective effect of all the stimuli on CD27^– B cells and the protective effect of CpG‐ODN and anti‐IgM on CD27⁺ B cells. In contrast, IL‐21 rescued unstimulated CD27^– B cells and improved the rescue of anti‐CD40‐stimulated CD27⁺ B cells. When we compared patients and controls, mainly CD27⁺ B cells from MB0 patients were less sensitive to rescue from apoptosis than those from MB1 patients and controls after activation, irrespective of the IL‐21 effect. Increased apoptosis during an immune response could result in lower levels of immunoglobulin production in these patients.     

Human blood dendritic cells from allergic subjects have impaired capacity to produce interferon-α via toll-like receptor 9

Background High‐affinity IgE receptor (Fc?RI) expression on blood dendritic cells reportedly correlates with serum IgE levels. Our studies demonstrate that plasmacytoid dendritic cells (pDCs) secrete pro‐inflammatory cytokines (IL‐6, TNF‐α) following Fc?RI stimulation – a mode of activation that simultaneously reduces expression of Toll‐like receptor 9 (TLR9). Whether or not TLR9 and/or Fc?RI levels and their function on dendritic cells relate to allergic status is unknown. Objective The aim of this study is to compare the innate (TLR9‐mediated) immune response of human pDCs to TLR9 and Fc?RIα receptor expression in allergic and non‐allergic subjects. Methods Basophil‐depleted mononuclear cell fractions containing pDCs were prepared from peripheral blood of allergic and non‐allergic subjects. Intracellular TLR9 and surface Fc?RIα expression in blood dendritic cell antigen‐2‐positive cells were determined by flow cytometry. Activating anti‐IgE antibody, anti‐Fc?RIα antibody, and TLR9 agonist were used to stimulate cell suspensions, with cytokine levels determined by ELISA. Results No difference in the frequency of pDCs was detected among allergic (n=9) vs. non‐allergic (n=11) subjects (P=0.261). While there was also no difference in the baseline expression of TLR9, pDCs from allergic subjects produced sixfold less IFN‐α when stimulated with CpG (P=0.002). Conversely, there was higher Fc?RIα expression (P=0.01) on the pDCs of allergic subjects. Conclusions Impaired TLR9‐dependent immune responses in human pDCs are associated with allergic status and inversely correlated with Fc?RIα expression. This impaired innate immune response among dendritic cells of allergic subjects may lead to more targeted therapeutic approaches and could provide a better understanding of the mechanisms underlying conventional and CpG‐based immunotherapy.     

Anti-tumour synergy of cytotoxic chemotherapy and anti-CD40 plus CpG-ODN immunotherapy through repolarization of tumour-associated macrophages

We studied the effectiveness of monoclonal anti‐CD40 + cytosine–phosphate–guanosine‐containing oligodeoxynucleotide 1826 (CpG‐ODN) immunotherapy (IT) in mice treated with multidrug chemotherapy (CT) consisting of vincristine, cyclophosphamide and doxorubicin. Combining CT with IT led to synergistic anti‐tumour effects in C57BL/6 mice with established B16 melanoma or 9464D neuroblastoma. CT suppressed the functions of T cells and natural killer (NK) cells, but primed naïve peritoneal macrophages (Mφ) to in vitro stimulation with lipopolysaccharide (LPS), resulting in augmented nitric oxide (NO) production. IT, given after CT, did not restore the responsiveness of T cells and NK cells, but further activated Mφ to secrete NO, interferon‐γ (IFN‐γ) and interleukin (IL)‐12p40 and to suppress the proliferation of tumour cells in vitro. These functional changes were accompanied by immunophenotype alterations on Mφ, including the up‐regulation of Gr‐1. CD11b⁺ F4/80⁺ Mφ comprised the major population of B16 tumour‐infiltrating leucocytes. CT + IT treatment up‐regulated molecules associated with the M1 effector Mφ phenotype [CD40, CD80, CD86, major histocompatibility complex (MHC) class II, IFN‐γ, tumour necrosis factor‐α (TNF‐α) and IL‐12] and down‐regulated molecules associated with the M2 inhibitory Mφ phenotype (IL‐4Rα, B7‐H1, IL‐4 and IL‐10) on the tumour‐associated Mφ compared with untreated controls. Together, the results show that CT and anti‐CD40 + CpG‐ODN IT synergize in the induction of anti‐tumour effects which are associated with the phenotypic repolarization of tumour‐associated Mφ.     

The CD20 homolog Ms4a8a integrates pro‐ and anti‐inflammatory signals in novel M2‐like macrophages and is expressed in parasite infection

Recently, we identified the CD20 homolog Ms4a8a as a novel molecule expressed by tumor‐associated macrophages that directly enhances tumor growth. Here, we analyzed Ms4a8a⁺ macrophages in M2‐associated infectious pathologies. In late‐stage Trypanosoma congolense and Taenia crassiceps infections, Ms4a8a expression was detected in hepatic and peritoneal macrophages respectively. Innate immunity in these infections is modulated by Toll‐like receptor (TLR) signaling and TLR2/4/7 agonists strongly induced Ms4a8a expression in bone marrow derived macrophages (BMDMs) treated with M2 mediators (glucocorticoids/IL‐4). LPS/dexamethasone/IL‐4‐induced Ms4a8a⁺ BMDMs were characterized by strong expression of mRNA of mannose receptor (Mmr), arginase 1, and CD163, and by decreased iNOS expression. Coinduction of Ms4a8a by M2 mediators and TLR agonists involved the classical TLR signaling cascade via activation of MyD88/TRIF and NF‐κB. Forced overexpression of Ms4a8a modulated the TLR4 response of RAW264.7 cells as shown by gene expression profiling. Upregulation of Hdc, Tcfec, and Sla was confirmed both in primary LPS/dexamethasone/IL‐4‐stimulated Ms4a8a⁺ BMDMs and in peritoneal macrophages from late‐stage Taenia crassiceps infection. In conclusion, we show that TLR signaling skews the typical alternative macrophage activation program to induce a special M2‐like macrophage subset in vitro that also occurs in immunomodulatory immune reactions in vivo, a process directly involving the CD20 homolog Ms4a8a.     

Th1 cytokines are more effective than Th2 cytokines at licensing anti‐tumour functions in CD40‐activated human macrophages in vitro

CD40 agonists are showing activity in early clinical trials in patients with advanced cancer. In animal models, CD40 agonists synergise with T‐cell‐activating therapies to inhibit tumour growth by driving tumour macrophage repolarisation from an immunosuppressive to a Th1 immunostimulatory, tumouricidal phenotype. We therefore tested the hypothesis that T‐cell‐derived cytokines license anti‐tumour functions in CD40‐activated human macrophages. CD40 ligand (CD40L) alone activated macrophages to produce immunosuppressive IL‐10, in a similar fashion to bacterial LPS, but failed to promote anti‐tumour functions. The Th1 cytokine IFN‐γ optimally licensed CD40L‐induced macrophage anti‐tumour functions, inducing a switch from IL‐10 to IL‐12p70 production, promoting macrophage‐mediated Th1 T‐cell skewing and enhancing tumouricidal activity. We found that even the Th2 cytokines IL‐4 and IL‐13 promoted IL‐12p70 production (albeit without inhibiting IL‐10 production) and enhanced Th1 T‐cell skewing by CD40L‐activated macrophages. However, IL‐4 and IL‐13 did not enhance tumouricidal activity in CD40L‐activated macrophages. Thus, while both Th1 and Th2 cytokines biased macrophages to a Th1 immunostimulatory phenotype, only Th1 cytokines promoted tumouricidal activity in CD40L‐activated macrophages. The presence of tumour‐infiltrating Th1 or Th2 cells might therefore be predictive for patient response to CD40 agonism.     

Avian-specific TLRs and downstream effector responses to CpG-induction in chicken macrophages

Chickens possess toll-like receptor (TLR15), a pattern recognition receptor (PRR) absent in mammals. We characterized the regulation and mechanism of CpG responsiveness via TLRs in chicken macrophage HD11 cells. TLR15 was significantly upregulated after induction with B- and C-type CpG oligonucleotides (ODN), tripalmitoylated lipopeptide (PAM3CSK4), Escherichia coli- and Salmonella enteritidis-derived lipopolysaccharide (LPS). In response to CpG-ODN inhibitor, TLR15 and IL1B were downregulated, but TLR21 was upregulated. IL1B was upregulated with CpG-ODN and downregulated after inhibitor treatment. The results suggest that responsiveness to different types of CpG-ODN in chicken macrophages requires multiple receptors, each with unique variation in expression. We utilized RNA interference (RNAi) technology to examine myeloid differentiation primary response gene (MyD88) dependency of TLR15 and TLR21. HD11 macrophages transfected with multiple MyD88-target siRNAs exhibited 70% decrease in MyD88 mRNA expression. IL1B was upregulated with CpG induction in cells with no reduction of MyD88 mRNA levels, but not in cells with 70% MyD88 reduction. Therefore, induction through TLR15 in response to CpG-ODN operates via the MyD88-dependent pathway in chicken macrophages.     

TELOMERE-INDEPENDENT REDUCTION OF HUMAN B LYMPHOCYTE: PROLIFERATION DURING LONG-TERM CULTURE

Toll‐like receptors (TLRs) and other pattern‐recognition receptors (PRRs) of the innate immune system form functional receptor complexes that recognize and respond to pathogen‐associated molecular patterns (PAMPs). Porphyromonas gingivalis is an important pathogen in human periodontitis and has also been implicated in atherosclerosis. A major virulence factor of this pathogen is the fimbriae, which function as a surface adhesin. Here we present evidence that fimbriae also constitute a predominant P. gingivalis proinflammatory molecule which activates the TLR signaling pathway resulting in induction of proinflammatory cytokines (IL‐1β, IL‐6, and TNF‐α) and chemokines (IL‐8) in monocytic cells. Although TLR2 and TLR4 mediate cellular activation in response to fimbriae, other PRRs, namely CD14 and CD11b/CD18, are involved in the recognition of fimbriae. We thus propose that fimbriae function as a PAMP which interacts with a PRR multi‐receptor complex, where CD14 and CD11b/CD18 function as recruiting receptors and TLRs function as signaling receptors. In addition to cytokine induction, TLR activation by fimbriae also results in upregulation of the CD40, CD80, and CD86 costimulatory molecules in antigen‐presenting cells, suggesting that fimbriae are sensed as a potential “danger” to the host immune system. Moreover, proinflammatory cytokine induction is attenuated upon repeated cellular stimulation with P. gingivalis fimbriae. This mechanism of tolerance induction which serves to mitigate excessive and potentially harmful inflammatory reactions appears to be due partly to fimbria‐induced downregulation of the expression of interleukin‐1 receptor‐associated kinase‐1 (IRAK‐1), an important signaling intermediate of the TLR pathway. Understanding the molecular basis of how the host recognizes and responds to P. gingivalis fimbriae is essential for developing molecular approaches to control P. gingivalis‐induced inflammatory responses in periodontal disease and perhaps atherosclerosis.     

Toll-like receptor 9 contributes to recognition of Mycobacterium bovis Bacillus Calmette-Guérin by Flt3-ligand generated dendritic cells

Recognition of mycobacteria by the innate immune system is essential for the development of an adaptive immune response. Mycobacterial antigens stimulate antigen presenting cells (APCs) through distinct Toll-like receptors (TLRs) resulting in rapid activation of the innate immune system. The role of TLRs during infection with Mycobacterium bovis Bacillus Calmette-Guérin (BCG) has been evaluated for TLR2 and TLR4 only. Surprisingly, despite the fact that immune stimulatory CpG-motifs have been originally derived from BCG, for the vaccine strain the role of TLR9 has not been addressed before. To identify the set of TLRs involved in the recognition of BCG, we infected bone marrow-derived macrophages and bone marrow-derived dendritic cells (Flt3-ligand generated DCs) from TLR2, TLR3, TLR4, TLR7, TLR9, MyD88 knockout, TLR2/4 and TLR2/4/9 multiple knockout mice. The degree of activation and stimulation was determined by TNFα, IL-6 and IL-12p40 ELISA. Activation of DCs was measured by surface expression of the costimulatory molecule CD86. We observed the most dramatic reduction of the inflammatory response for TLR2-deficient antigen presenting cells. Both macrophages and DCs produce markedly decreased amounts of TNFα and IL-6 in the absence of TLR2 whereas no significant reduction could be observed for TLR3, 4, 7, 9 single TLR-knockouts. However, IL-12 production in DCs appears not exclusively dependent on TLR2 and only in TLR2/4/9-deficient DCs BCG-induced IL-12 is reduced to background levels. Similarly, up-regulation of CD86 is abolished only in TLR2/4/9-deficient DCs supporting a role of TLR9 in the recognition of M. bovis BCG by murine dendritic cells.