A hypervariable N-terminal region of Yersinia LcrV determines Toll-like receptor 2-mediated IL-10 induction and mouse virulence

Deciphering the Role of Leptospira Surface Protein LigA in Modulating the Host Innate Immune Response

Leptospira, a zoonotic pathogen, is known to infect various hosts and can establish persistent infection. This remarkable ability of bacteria is attributed to its potential to modulate (activate or evade) the host immune response by exploiting its surface proteins. We have identified and characterized the domain of the variable region of Leptospira immunoglobulin-like protein A (LAV) involved in immune modulation. The 11^th domain (A₁₁) of the variable region of LigA (LAV) induces a strong TLR4 dependent innate response leading to subsequent induction of humoral and cellular immune responses in mice. A₁₁ is also involved in acquiring complement regulator FH and binds to host protease Plasminogen (PLG), there by mediating functional activity to escape from complement-mediated killing. The deletion of A₁₁ domain significantly impaired TLR4 signaling and subsequent reduction in the innate and adaptive immune response. It also inhibited the binding of FH and PLG thereby mediating killing of bacteria. Our study discovered an unprecedented role of LAV as a nuclease capable of degrading Neutrophil Extracellular Traps (NETs). This nuclease activity was primarily mediated by A₁₁. These results highlighted the moonlighting function of LigA and demonstrated that a single domain of a surface protein is involved in modulating the host innate immune defenses, which might allow the persistence of Leptospira in different hosts for a long term without clearance.

Systematic analysis, identification, and use of CRISPR/Cas13a-associated crRNAs for sensitive and specific detection of the lcrV gene of Yersinia pestis

CRISPR-associated proteins that produce a signal in the presence of a target nucleic acid represent potentially powerful tools for diagnostics, but they also exhibit shortfalls that plague many CRISPR systems. For instance, not all targets elicit robust activity, which challenges the timely development of sensitive assays, and though many such tests have been reported, they often avoid discussion of the crRNA design and screening process. Here, motivated by the desire to detect the Yersinia pestis lcrV virulence gene, we detail the process involved in developing components for a CRISPR-based test that provides sensitive and specific identification of this sequence using Cas13a. This includes detailing the diversity of crRNA performance, identifying sequence that enable detection with attomolar sensitivity and species-level specificity, and presenting a method for simple streamlining of the crRNA screening process to allow for the high-throughput testing required for developing assay design rules in the future.

Vaccine Potential of a Recombinant Bivalent Fusion Protein LcrV-HSP70 Against Plague and Yersiniosis

To counteract the deadly pathogens, i.e., Y. pestis, Y. enetrocolitica, and Y. pseudotuberculosis, we prepared a recombinant DNA construct lcrV-hsp70 encoding the bivalent fusion protein LcrV-HSP70. The lcrV gene of Y. pestis and hsp70 domain II DNA fragment of M. tuberculosis were amplified by PCR. The lcrV amplicon was first ligated in the pET vector using NcoI and BamHI restriction sites. Just downstream to the lcrV gene, the hsp70 domain II was ligated using BamHI and Hind III restriction sites. The in-frame and the orientation of cloned lcrV-hsp70 were checked by restriction analysis and nucleotide sequencing. The recombinant bivalent fusion protein LcrV-HSP70 was expressed in E. coli and purified by affinity chromatography. The vaccine potential of LcrV-HSP70 fusion protein was evaluated in formulation with alum. BALB/c mice were vaccinated, and the humoral and cellular immune responses were studied. The fusion protein LcrV-HSP70 induced a strong and significant humoral immune response in comparison to control animals. We also observed a significant difference in the expression levels of IFN-γ and TNF-α in LcrV–HSP70-immunized mice in comparison to control, HSP70, and LcrV groups. To test the protective efficacy of the LcrV–HSP70 fusion protein against plague and Yersiniosis, the vaccinated mice were challenged with Y. pestis, Y. enterocolitica, and Y. pseudotuberculosis separately. The bivalent fusion protein LcrV–HSP70 imparted 100% protection against the plague. In the case of Yersiniosis, on day 2 post challenge, there was a significant reduction in the number of CFU of Y. enterocolitica and Y. pseudotuberculosis in the blood (CFU/ml) and the spleen (CFU/g) of vaccinated animals in comparison to the LcrV, HSP70, and control group animals.

Interactions between Yersinia pestis V-antigen (LcrV) and human Toll-like receptor 2 (TLR2) in a modelled protein complex and potential mechanistic insights

Background

Yersinia pestis, the etiological pathogen of plague, is capable of repressing the immune response of white blood cells to evade phagocytosis. The V-antigen (LcrV) was found to be involved in this process by binding to human Toll-like Receptor 2 (TLR2). The detailed mechanism behind this LcrV and TLR2 mediated immune response repression, however, is yet to be fully elucidated due to the lack of structural information.

Results

In this work, with protein structure modelling, we were able to construct a structure model of the heterotetramer of Y. pestis LcrV and human TLR2. Molecular dynamics simulation suggests the stability of this structure in aquatic environment. The LcrV model has a dumbbell-like structure with two globule domains (G1 at N-terminus and G2 away from membrane) connected with a coiled-coil linker (CCL) domain. The two horseshoe-shape TLR2 subunits form a V-shape structure, are not in direct contact with each other, and are held together by the LcrV homodimer. In this structure model, both the G1 and CCL domains are involved in the formation of LcrV homodimer, while all three domains are involved in LcrV-TLR2 binding. A mechanistic model was proposed based on this heterotetrameric structure model: The LcrV homodimer separates the TLR2 subunits to inhibit the dimerization of TLR2 and subsequent signal transfer for immune response; while LcrV could also inhibit the formation of heterodimers of TLR2 with other TLRs, and leads to immune response repression.

Conclusions

A heterotetrameric structure of Y. pestis LcrV and human TLR2 was modelled in this work. Analysis of this modelled structure showed its stability in aquatic environments and the role of LcrV domains and residues in protein-protein interaction. A mechanistic model for the role of LcrV in Y. pestis pathogenesis is raised based on this heterotetrameric structure model. This work provides a hypothesis of LcrV function, with which further experimental validation may elucidate the role of LcrV in human immune response repression.

S-Layer Protein of Lactobacillus helveticus SBT2171 Promotes Human β-Defensin 2 Expression via TLR2-JNK Signaling

Antimicrobial peptides that contribute to innate immunity are among the most important protective measures against infection in many organisms. Several substances are known to regulate the expression of antimicrobial peptides. In this study, we investigated the factors in lactic acid bacteria (LAB) that induce antimicrobial peptide expression in the host. We found that Lactobacillus helveticus SBT2171 (LH2171) induced the expression of human β-defensin (hBD)2 in Caco-2 human colonic epithelial cells. Specifically, surface layer protein (SLP) of LH2171 stimulated hBD2 expression by activating c-Jun N-terminal kinase (JNK) signaling via Toll-like receptor (TLR)2 in Caco-2 cells. SLPs extracted from other lactobacilli similarly increased hBD2 expression, suggesting that this stimulatory effect is common feature of Lactobacillus SLPs. Interestingly, Lactobacillus strains that strongly induced hBD2 expression also potently activated JNK signaling. Thus, upregulation of hBD2 induced by TLR2–JNK signaling contributes to protection of the host against infection.

Polymorphism in the Yersinia LcrV Antigen Enables Immune Escape From the Protection Conferred by an LcrV-Secreting Lactococcus Lactis in a Pseudotuberculosis Mouse Model

Yersinioses caused by Yersinia pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica are significant concerns in human and veterinary health. The link between virulence and the potent LcrV antigen has prompted the latter's selection as a major component of anti-Yersinia vaccines. Here, we report that (i) the group of Yersinia species encompassing Y. pestis and Y. pseudotuberculosis produces at least five different clades of LcrV and (ii) vaccination of mice with an LcrV-secreting Lactococcus lactis only protected against Yersinia strains producing the same LcrV clade as that of used for vaccination. By vaccinating with engineered LcrVs and challenging mice with strains producing either type of LcrV or a LcrV mutated for regions of interest, we highlight key polymorphic residues responsible for the absence of cross-protection. Our results show that an anti-LcrV-based vaccine should contain multiple LcrV clades if protection against the widest possible array of Yersinia strains is sought.

Subtractive proteomics and immunoinformatics revealed novel B-cell derived T-cell epitopes against Yersinia enterocolitica: An etiological agent of Yersiniosis

Yersinia enterocolitica is the third most common cause of gastrointestinal manifestations in Europe. Statistically, every year the pathogen accounts for 640 hospitalizations, 117,000 illnesses, and 35 deaths in the United States. The associated mortality rate of the pathogen is 50% and is virtually resistant to penicillin G, ampicillin and cephalotin. The development of new and effective therapeutic procedures is urgently needed to counter the multi-drug-resistant phenotypes imposed by the said pathogen. Based on subtractive reverse vaccinology and immunoinformatics approaches, we have successfully predicted novel antigenic peptide vaccine candidates against Y. enterocolitica. The pipeline revealed two isoforms of ompC family; meoA (ompC) and ompC2 as promising vaccine targets. Protein-protein interactions elaborated the involvement of target candidates in the major biological pathways of the pathogen. The predicted 9-mer B-cell derived T-cell epitope of proteins are found to be virulent, antigenic, non-allergic, surface exposed and conserved in all nine completely sequenced strains of the pathogen. Molecular docking predicts deep and stable binding of the epitopes in the binding pocket of the most predominant allele in human population-the DRB1*0101. These epitopes of target proteins could provide the foundation for the development of an epitope-driven vaccine against Y. enterocolitica.

T cell-intrinsic TLR2 stimulation promotes IL-10 expression and suppressive activity by CD45RbHi T cells

While Toll-like receptors (TLRs) represent one of the best characterized innate immune pathways, evidence suggests that TLRs are not restricted to innate leukocytes and some epithelial cells, but are also expressed in T cells. Specifically, published evidence focusing on FoxP3⁺ regulatory T cells demonstrate that they express functional TLR2, which is already known among the TLR family for its association with immune suppression; however, little is known about the relationship between T cell-intrinsic TLR2 binding and cytokine production, T cell differentiation, or T cell receptor (TCR) stimulation. Here, we demonstrate that TCR and TLR2 co-stimulation provides a T cell-intrinsic signal which generates a dramatic, synergistic cytokine response dominated by IL-10. Importantly, the response was not seen in either CD4⁺CD25⁺ or CD4⁺FoxP3⁺ Tregs, yet resulted in the expansion of a suppressive CD4⁺CD25⁺CD62L^-CD44⁺CD45Rb^hi effector/memory T cell subset not typically associated with immune inhibition. This study reveals the striking ability of a prototypical innate immune receptor to trigger a potent and suppressive IL-10 response in effector/memory T cells, supporting the notion that TLR2 is a co-regulatory receptor on T cells.

A study on the efficacy of the recombinant Yersinia adhesin A vaccine against yersiniosis in the early phase

Yersinia pseudotuberculosis (Y. ptb) is a zoonotic pathogenic bacterial species of the family Enterobacteriaceae and causes yersiniosis, an acute intestinal infection in humans and animals. Y. ptb is often implicated in lethal epidemics in zoo animals and reductions in the breeding population, but a valid prevention method has not been established. Therefore, this study aimed to develop a vaccine for yersiniosis control. The immunogenicity of one of the adhesion factors involved in pathogenic mechanisms of Y. ptb, Yersinia adhesin A (YadA), was investigated. BALB/c mice were divided into 3 groups: in group 1, mice received insoluble recombinant YadA (rYadA) produced in genetically engineered Escherichia coli (100 µg/dose); in group 2, mice received inactivated Y. ptb with strong expression of YadA (20 mg/dose);and in group 3, mice received phosphate-buffered saline (0.2 ml/dose). All interventions were administered subcutaneously twice at an interval of 1 week. One week after the second administration, Y. ptb (10⁷ cells/mouse) was inoculated orally. As a result, the survival rate was 100% in group 1, 60% in group 2, and 0% in group 3. The anti-YadA antibody titer increased in a stepwise fashion in groups 1 and 2. The present study results suggest that rYadA shows promise as a protective antigen against yersiniosis. This study concluded that vaccination against Y. ptb may become available as a new method to prevent lethal epidemics in animals.

Anti-inflammatory activities of Ganoderma lucidum (Lingzhi) and San-Miao-San supplements in MRL/lpr mice for the treatment of systemic lupus erythematosus

BACKGROUND

Ganoderma lucidum (Lingzhi; LZ) and San-Miao-San (SMS) are Chinese medicines (CMs) used to treat inflammatory ailments and numbing syndrome/arthralgia syndrome (Bi Zheng), respectively. Given that the main symptoms of systemic lupus erythematosus (SLE) include inflammation of the joints, joint pain, edema and palpitations of the heart because of problems associated with Bi Zheng, it was envisaged that LZ and SMS could be used as potential treatments for this autoimmune disease. This study aims to investigate the anti-inflammatory activity of a combination formulation containing LZ and SMS (LZ-SMS) in SLE mice.

METHODS

Female adult Balb/c mice of 20-24 weeks of age were used as normal mice (n = 10), whereas female MRL/lpr mice of 12-24 weeks of age were divided into three groups (n = 10 in each group), including mild, moderate and severe SLE mice groups. The clinical characteristics of the SLE and Babl/c mice (i.e., body weight, joint thickness, lupus flare, proteinuria, leukocyturia and lymphadenopathy) were assessed. The plasma concentrations of anti-nuclear antibody (ANA) and anti-double stranded DNA antibody (anti-ds-DNA) were analyzed by an enzyme-linked immunosorbent assay, whereas the concentration of several key cytokines (IFN-γ, TNF-α, IL-6, IL-10, IL-2, IL-27, IL-12P70, IL-17A and IL-21) were analyzed by a Luminex multiplex assay. The gene expression profiles for differentiation of the T helper (Th) lymphocytes in splenic CD4(+) Th cells were assessed by RT-qPCR. Flow cytometry was used to measure the percentages of CD4(+)CD25(+)Foxp3(+) Treg cells and CD19(+)CD5(+)CD1d(+)IL-10(+) regulatory B (Breg) cells (IL-10(+) Bregs).

RESULTS

Concentrations of anti-ds-DNA in the plasma samples collected from the LZ-SMS-treated (500 mg/kg/day oral administration for 7 days followed with 50 mg/kg/day intraperitoneal administration for 7 days), moderate and severe SLE mice decreased significantly compared with the PBS treated mice (P < 0.05). The gene expression levels of the induced regulatory T (iTreg) and natural Treg (nTreg) cells were significantly higher than those of the Th17, Th1 and "conventional Th cells vs. Treg cells" regulated genes following the LZ-SMS treatment (P < 0.05). The percentages of CD4(+)CD25(+)Foxp3(+) Treg cells collected from the splenic, thymic and peripheral blood cells, as well as the percentages of IL-10(+) Bregs collected from the splenic and thymic cells increased significantly in the LZ-SMS-treated SLE mice (P < 0.05) compared with the untreated PBS group. The ratio of the percentage of CD4(+)CD25(+)Foxp3(+) Treg cells to the percentage of CD4(+)CD25(-) effector T cells collected from the splenic, thymic and peripheral blood cells in LZ-SMS-treated moderate and severe SLE mice increased significantly compared with the untreated PBS group (P < 0.05). Furthermore, a comparison with the PBS treatment group revealed significant decreases in the concentrations of several inflammatory cytokines, including IL-21, IL-10 and IL-17A (P < 0.05), as well as significant increases in the concentrations of IL-2 and IL-12P70 in the LZ-SMS treated SLE mice (P < 0.05).

CONCLUSION

LZ-SMS treatment led to significant increases in the percentages of CD4(+)CD25(+)Foxp3(+) Treg and IL-10(+) Breg cells, together with a reduction in the plasma concentrations of several inflammatory cytokines and the down-regulated expression of the corresponding cytokine related genes in SLE mice. The clinical characteristics of the LZ-SMS-treated SLE mice also improved significantly.

Recombinant Bivalent Fusion Protein rVE Induces CD4+ and CD8+ T-Cell Mediated Memory Immune Response for Protection Against Yersinia enterocolitica Infection

Studies investigating the correlates of immune protection against Yersinia infection have established that both humoral and cell mediated immune responses are required for the comprehensive protection. In our previous study, we established that the bivalent fusion protein (rVE) comprising immunologically active regions of Y. pestis LcrV (100–270 aa) and YopE (50–213 aa) proteins conferred complete passive and active protection against lethal Y. enterocolitica 8081 challenge. In the present study, cohort of BALB/c mice immunized with rVE or its component proteins rV, rE were assessed for cell mediated immune responses and memory immune protection against Y. enterocolitica 8081. rVE immunization resulted in extensive proliferation of both CD4 and CD8 T cell subsets; significantly high antibody titer with balanced IgG1: IgG2a/IgG2b isotypes (1:1 ratio) and up-regulation of both Th1 (TNF-α, IFN-γ, IL-2, and IL-12) and Th2 (IL-4) cytokines. On the other hand, rV immunization resulted in Th2 biased IgG response (11:1 ratio) and proliferation of CD4+ T-cell; rE group of mice exhibited considerably lower serum antibody titer with predominant Th1 response (1:3 ratio) and CD8+ T-cell proliferation. Comprehensive protection with superior survival (100%) was observed among rVE immunized mice when compared to the significantly lower survival rates among rE (37.5%) and rV (25%) groups when IP challenged with Y. enterocolitica 8081 after 120 days of immunization. Findings in this and our earlier studies define the bivalent fusion protein rVE as a potent candidate vaccine molecule with the capability to concurrently stimulate humoral and cell mediated immune responses and a proof of concept for developing efficient subunit vaccines against Gram negative facultative intracellular bacterial pathogens.

Transcriptomic response to Yersinia pestis: RIG-I like receptor signaling response is detrimental to the host against plague

Bacterial pathogens have evolved various mechanisms to modulate host immune responses for successful infection. In this study, RNA-sequencing technology was used to analyze the responses of human monocytes THP1 to Yersinia pestis infection. Over 6000 genes were differentially expressed over the 12 h infection. Kinetic responses of pathogen recognition receptor signaling pathways, apoptosis, antigen processing, and presentation pathway and coagulation system were analyzed in detail. Among them, RIG-I-like receptor (RLR) signaling pathway, which was established for antiviral defense, was significantly affected. Mice lacking MAVS, the adaptor of the RLR signaling pathway, were less sensitive to infection and exhibited lower IFN-β production, higher Th1-type cytokines IFN-γ and IL-12 production, and lower Th2-type cytokines IL-4 and IL-13 production in the serum compared with wild-type mice. Moreover, infection of pathogenic bacteria other than Y. pestis also altered the expression of the RLR pathway, suggesting that the response of RLR pathway to bacterial infection is a universal mechanism.

Infection-induced IL-10 and JAK-STAT: A review of the molecular circuitry controlling immune hyperactivity in response to pathogenic microbes

Generation of effective immune responses against pathogenic microbes depends on a fine balance between pro- and anti-inflammatory responses. Interleukin-10 (IL-10) is essential in regulating this balance and has garnered renewed interest recently as a modulator of the response to infection at the JAK-STAT signaling axis of host responses. Here, we examine how IL-10 functions as the “master regulator” of immune responses through JAK-STAT, and provide a perspective from recent insights on bacterial, protozoan, and viral infection model systems. Pattern recognition and subsequent molecular events that drive activation of IL-10-associated JAK-STAT circuitry are reviewed and the implications for microbial pathogenesis are discussed.

Rabbit monoclonal antibodies directed at the T3SS effector protein YopM identify human pathogenic Yersinia isolates

The Yersinia outer protein M (YopM) is a type 3 secretion system (T3SS)-dependent effector protein of Yersinia enterocolitica, Yersinia pseudotuberculosis and Yersinia pestis. Although YopM is indispensable for full virulence, its molecular functions still remain largely elusive. Recently, we could identify the recombinant YopM (rYopM) protein derived from the Y. enterocolitica strain 8081 (JB580) as a cell-penetrating protein, which down-regulates the expression of various pro-inflammatory cytokines including TNFα. In this study, we have generated rabbit monoclonal anti-YopM antibodies (RabMabs). RabMabs were characterized by SDS-PAGE and Western blotting using various truncated versions of rYopM to identify epitope-containing domains. RabMabs recognizing either the N- or C-terminus of YopM were characterized further and validated using a collection of 61 pathogenic and non-pathogenic Yersinia strains as well as exemplary strains of major intestinal bacterial pathogens such as Salmonella enterica ssp. enterica, Shigella flexneri and intestinal pathogenic Escherichia coli. RabMab 41.3 directed at the N-terminus of YopM of Y. enterocolitica strain 8081 recognized all YopM-expressing pathogenic Yersinia strains analyzed in this study but failed to recognize non-pathogenic isolates. Thus, RabMab 41.3 might be applicable for the detection of pathogenic Yersinia strains.

RIP2/RICK-dependent cytokine production upon Yersinia enterocolitica infection in macrophages with TLR4 deficiency

Receptor-interacting protein 2 (RIP2) is a caspase recruitment domain (CARD)-containing serine/threonine kinase that is activated by NOD1 or NOD2 recognition of their ligands and essential for the activation of NF-κB and mitogen-activated protein kinase (MAPK). RIP2 has been known to play an important role in innate immune responses against certain bacterial infection. However, the role and interplay of RIP2 with TLR signalling on cytokine production in macrophages against Yersinia enterocolitica infection remains poorly understood. In the present study, we examined whether RIP2 is essential for Yersinia-induced production of cytokines in macrophages. Our results showed that naïve RIP2-deficient macrophages produced similar level of IL-6, TNF-α and IL-10 upon Y. enterocolitica infection compared with wild-type macrophages. However, the production of IL-6, TNF-α and IL-10 by Y. enterocolitica was impaired in RIP2-deficient macrophages after lipopolysaccharide (LPS) pretreatment, a TLR4-tolerant condition. In addition, RIP2 inhibitors, SB203580, PP2, and gefitinib, reduced IL-6 production in TLR4-deficient macrophages in response to Y. enterocolitica, whereas they did not affect the cytokines production in WT cells. These results demonstrate that RIP2 may play an important role in proinflammatory cytokine production in macrophages at the absence of TLR signalling.

Human and animal isolates of Yersinia enterocolitica show significant serotype-specific colonization and host-specific immune defense properties

Yersinia enterocolitica is a human pathogen that is ubiquitous in livestock, especially pigs. The bacteria are able to colonize the intestinal tract of a variety of mammalian hosts, but the severity of induced gut-associated diseases (yersiniosis) differs significantly between hosts. To gain more information about the individual virulence determinants that contribute to colonization and induction of immune responses in different hosts, we analyzed and compared the interactions of different human- and animal-derived isolates of serotypes O:3, O:5,27, O:8, and O:9 with murine, porcine, and human intestinal cells and macrophages. The examined strains exhibited significant serotype-specific cell binding and entry characteristics, but adhesion and uptake into different host cells were not host specific and were independent of the source of the isolate. In contrast, survival and replication within macrophages and the induced proinflammatory response differed between murine, porcine, and human macrophages, suggesting a host-specific immune response. In fact, similar levels of the proinflammatory cytokine macrophage inflammatory protein 2 (MIP-2) were secreted by murine bone marrow-derived macrophages with all tested isolates, but the equivalent interleukin-8 (IL-8) response of porcine bone marrow-derived macrophages was strongly serotype specific and considerably lower in O:3 than in O:8 strains. In addition, all tested Y. enterocolitica strains caused a considerably higher level of secretion of the anti-inflammatory cytokine IL-10 by porcine than by murine macrophages. This could contribute to limiting the severity of the infection (in particular of serotype O:3 strains) in pigs, which are the primary reservoir of Y. enterocolitica strains pathogenic to humans.

Editorial: A Toll gate to escape T cells

Discussion of how the subversive actions of P. gingivalis include manipulation of initial adaptive immune response.

Amino acid substitutions in LcrV at putative sites of interaction with Toll-like receptor 2 do not affect the virulence of Yersinia pestis

LcrV, a component of the type III secretion system (T3SS) translocon in Yersinia pestis, has been concerned in suppressing inflammation through Toll-like receptor 2 (TLR2) by inducing expression of the anti-inflammatory cytokine interleukin-10 (IL-10). Previous studies have reported that LcrV aa E33, E34, K42 and/or E204 and E205 were important for interactions with TLR2 in vitro. While, recently there have been conflicting reports doubting this interaction and its importance in vivo. To further investigate the role of these residues, we replaced the wild-type lcrV gene on the pCD1Ap virulence plasmid of Y. pestis with lcrV2345 gene, which encodes a mutant protein by substituting all five of the amino acid residues with glutamine. The characteristics of the wild-type LcrV and mutant LcrV2345 were evaluated in tissue culture and mice. When purified protein was incubated with HEK293 cells synthesizing human TLR2 with or without CD14, LcrV2345 induced higher levels of IL-8 than wild-type LcrV, indicating that the LcrV2345 was not impaired in its ability to interact with TLR2. LcrV2345 stimulated higher levels of tumor necrosis factor-alpha (TNF-α) production than LcrV in J774A.1 cells, while neither protein elicited significant levels of IL-10. We also found there was no statistically significant difference in virulence between strains with wild-type LcrV and with mutated LcrV2345 administered by either subcutaneous or intranasal route in mice. Additionally, there were no discernible differences in survival kinetics. Serum levels of cytokines, such as IL-10 and TNF-α, bacterial burden, and the extent of organ inflammation were also indistinguishable in both strains. Our data confirm that immunomodulation mediated by LcrV/TLR2 interactions does not play a significant role in the pathogenicity of Y. pestis.

Identification of a unique TLR2-interacting peptide motif in a microbial leucine-rich repeat protein

Pathogenesis of many bacterially-induced inflammatory diseases is driven by Toll-like receptor (TLR) mediated immune responses following recognition of bacterial factors by different TLRs. Periodontitis is a chronic inflammation of the tooth supporting apparatus often leading to tooth loss, and is caused by a Gram-negative bacterial consortium that includes Tannerella forsythia. This bacterium expresses a virulence factor, the BspA, which drives periodontal inflammation by activating TLR2. The N-terminal portion of the BspA protein comprises a leucine-rich repeat (LRR) domain previously shown to be involved in the binding and activation of TLR2. The objective of the current study was to identify specific epitopes in the LRR domain of BspA that interact with TLR2. Our results demonstrate that a sequence motif GC(S/T)GLXSIT is involved in mediating the interaction of BspA with TLR2. Thus, our study has identified a peptide motif that mediates the binding of a bacterial protein to TLR2 and highlights the promiscuous nature of TLR2 with respect to ligand binding. This work could provide a structural basis for designing peptidomimetics to modulate the activity of TLR2 in order to block bacterially-induced inflammation.

Interleukin-10 induction is an important virulence function of the Yersinia pseudotuberculosis type III effector YopM

Pathogenic Yersinia species modulate host immune responses through the activity of a plasmid-encoded type III secretion system and its associated effector proteins. One effector, YopM, is a leucine-rich-repeat-containing protein that is important for virulence in murine models of Yersinia infection. Although the mechanism by which YopM promotes virulence is unknown, we previously demonstrated that YopM was required for the induction of high levels of the immunosuppressive cytokine interleukin-10 (IL-10) in sera of C57BL/6J mice infected with Yersinia pseudotuberculosis. To determine if IL-10 production is important for the virulence function of YopM, C57BL/6J or congenic IL-10⁻/⁻ mice were infected intravenously with wild-type or yopM mutant Y. pseudotuberculosis strains. Analysis of cytokine levels in serum and bacterial colonization in the spleen and liver showed that YopM is required for IL-10 induction in C57BL/6J mice infected with either the IP32953 or the 32777 strain of Y. pseudotuberculosis, demonstrating that the phenotype is conserved in the species. In single-strain infections, the ability of the 32777ΔyopM mutant to colonize the liver was significantly increased by the delivery of exogenous IL-10 to C57BL/6J mice. In mixed infections, the competitive advantage of a yopM⁺ 32777 strain over an isogenic yopM mutant to colonize spleen and liver, as observed for C57BL/6J mice, was significantly reduced in IL-10⁻/⁻ animals. Thus, by experimentally controlling IL-10 levels in a mouse infection model, we obtained evidence that the induction of this cytokine is an important mechanism by which YopM contributes to Y. pseudotuberculosis virulence.

Immunomodulatory effects of Streptococcus suis capsule type on human dendritic cell responses, phagocytosis and intracellular survival

Streptococcus suis is a major porcine pathogen of significant commercial importance worldwide and an emerging zoonotic pathogen of humans. Given the important sentinel role of mucosal dendritic cells and their importance in induction of T cell responses we investigated the effect of different S. suis serotype strains and an isogenic capsule mutant of serotype 2 on the maturation, activation and expression of IL-10, IL-12p70 and TNF-α in human monocyte-derived dendritic cells. Additionally, we compared phagocytosis levels and bacterial survival after internalization. The capsule of serotype 2, the most common serotype associated with infection in humans and pigs, was highly anti-phagocytic and modulated the IL-10/IL-12 and IL-10/TNF-α cytokine production in favor of a more anti-inflammatory profile compared to other serotypes. This may have consequences for the induction of effective immunity to S. suis serotype 2 in humans. A shielding effect of the capsule on innate Toll-like receptor signaling was also demonstrated. Furthermore, we showed that 24 h after phagocytosis, significant numbers of viable intracellular S. suis were still present intracellularly. This may contribute to the dissemination of S. suis in the body.

Multi-Functional Characteristics of the Pseudomonas aeruginosa Type III Needle-Tip Protein, PcrV; Comparison to Orthologs in other Gram-negative Bacteria

Pseudomonas aeruginosa possesses a type III secretion system (T3SS) to intoxicate host cells and evade innate immunity. This virulence-related machinery consists of a molecular syringe and needle assembled on the bacterial surface, which allows delivery of T3 effector proteins into infected cells. To accomplish a one-step effector translocation, a tip protein is required at the top end of the T3 needle structure. Strains lacking expression of the functional tip protein fail to intoxicate host cells. P. aeruginosa encodes a T3S that is highly homologous to the proteins encoded by Yersinia spp. The needle-tip proteins of Yersinia, LcrV, and P. aeruginosa, PcrV, share 37% identity and 65% similarity. Other known tip proteins are AcrV (Aeromonas), IpaD (Shigella), SipD (Salmonella), BipD (Burkholderia), EspA (EPEC, EHEC), Bsp22 (Bordetella), with additional proteins identified from various Gram-negative species, such as Vibrio and Bordetella. The tip proteins can serve as a protective antigen or may be critical for sensing host cells and evading innate immune responses. Recognition of the host microenvironment transcriptionally activates synthesis of T3SS components. The machinery appears to be mechanically controlled by the assemblage of specific junctions within the apparatus. These junctions include the tip and base of the T3 apparatus, the needle proteins and components within the bacterial cytoplasm. The tip proteins likely have chaperone functions for translocon proteins, allowing the proper assembly of translocation channels in the host membrane and completing vectorial delivery of effector proteins into the host cytoplasm. Multi-functional features of the needle-tip proteins appear to be intricately controlled. In this review, we highlight the functional aspects and complex controls of T3 needle-tip proteins with particular emphasis on PcrV and LcrV.

TLR2 signaling improves immunoregulation to prevent type 1 diabetes

Signaling through TLR2 promotes inflammation and modulates CD4(+) CD25(+) Tregs. We assessed mechanistically how this molecule would alter immunoregulation in type 1 diabetes (T1D). We also asked whether TLR2 may be involved in our recent discovery that viral infection can protect from autoimmune diabetes by expanding and invigorating Tregs. Treatment of prediabetic mice with a synthetic TLR2 agonist diminished T1D and increased the number and function of CD4(+) CD25(+) Tregs, also conferring DCs with tolerogenic properties. TLR2 ligation also promoted the expansion of Tregs upon culture with DCs and ameliorated their capacity to prevent the disease. Protection from T1D by lymphocytic choriomeningitis virus (LCMV) infection depended on TLR2. LCMV increased the frequency of CD4(+) CD25(+) Tregs and their production of TGF-β more significantly in WT than TLR2-deficient mice. Furthermore, LCMV infection in vivo or LCMV-infected DCs in vitro rendered, via TLR2, CD4(+) CD25(+) Tregs capable of diminishing T1D. We identify novel mechanisms by which TLR2 promotes immunoregulation and controls autoimmune diabetes in naïve or infected hosts. This work should help understand T1D etiology and develop novel immune-based therapeutic interventions.

Microbial manipulation of receptor crosstalk in innate immunity

In the arms race of host-microbe co-evolution, successful microbial pathogens have evolved ingenious ways to evade host immune responses. In this Review, we focus on 'crosstalk manipulation' - the microbial strategies that instigate, subvert or disrupt the molecular signalling crosstalk between receptors of the innate immune system. This proactive interference undermines host defences and contributes to microbial adaptive fitness and persistent infections. Understanding how pathogens exploit host receptor crosstalk mechanisms and infiltrate the host signalling network is essential for developing interventions to redirect the host response and achieve protective immunity.

Anti-inflammatory modulation of immune response by probiotic Escherichia coli Nissle 1917 in human blood mononuclear cells

Escherichia coli Nissle 1917 (EcN) bears a defect in its LPS biosynthesis leading to truncated variable oligosaccharide-antigen chains and a semi-rough phenotype. It is effectively inactivated by complement factors due to resolved serum resistance and is, therefore, safe as a probiotic strain, i.e. for the treatment of inflammatory gastrointestinal diseases. It is unknown whether the modification of LPS in EcN contributes to its probiotic properties. Purified LPS from EcN and wild-type LPS from uropathogenic E. coli W536 together with raw lysates of both strains were analyzed for their gene expression activity with human PBMCs measured by microarrays. Comparing the two LPS molecules and the two lysate variants with each other, respectively, no differences of transcriptional patterns were observed. However, when comparing LPS with lysate patterns, pro-inflammatory cytokine IL-12p40 was up-regulated by both LPS molecules and anti-inflammatory IL-10 by both lysates. The higher the lysate concentration, the higher IL-10 release from PBMCs, clearly exceeding LPS induced IL-12p40 release. Furthermore, inflammatory chemokine CCL24 (eotaxin) was down-regulated by lysates and quantitative real-time PCR revealed that EcN compared to wild-type LPS was 8 times stronger in down-regulation of CCL24. We conclude that truncated LPS may down-regulate CCL24-mediated inflammation and that EcN lysate contains as yet unidentified factors which preferably induce anti-inflammatory activity. Both effects may contribute to the probiotic properties of EcN.

Evaluation of Psn, HmuR and a modified LcrV protein delivered to mice by live attenuated Salmonella as a vaccine against bubonic and pneumonic Yersinia pestis challenge

We evaluated the ability of Yersinia pestis antigens HmuR, Psn and modified forms of LcrV delivered by live attenuated Salmonella strains to stimulate a protective immune response against subcutaneous or intranasal challenge with Y. pestis CO92. LcrV196 is a previously described truncated protein that includes aa 131-326 of LcrV and LcrV5214 has been modified to replace five key amino acids required for interaction with the TLR2 receptor. Psn is the outer membrane receptor for the siderophore, yersiniabactin, and the bacteriocin, pesticin. Mice immunized with Salmonella synthesizing Psn, LcrV196 or LcrV5214 developed serum IgG responses to the respective Yersinia antigen and were protected against pneumonic challenge with Y. pestis. Immunization with Salmonella synthesizing Psn or LcrV196 was sufficient to afford nearly full protection against bubonic challenge, while immunization with the strain synthesizing LcrV5214 was not protective. Immunization with Salmonella synthesizing HmuR, an outer membrane protein involved in heme acquisition in Y. pestis, was poorly immunogenic and did not elicit a protective response against either challenge route. These findings indicate that both Psn and LcrV196 delivered by Salmonella provide protection against both bubonic and pneumonic plague.

Fine-tuning synthesis of Yersinia pestis LcrV from runaway-like replication balanced-lethal plasmid in a Salmonella enterica serovar typhimurium vaccine induces protection against a lethal Y. pestis challenge in mice

A balanced-lethal plasmid expression system that switches from low-copy-number to runaway-like high-copy-number replication (pYA4534) was constructed for the regulated delayed in vivo synthesis of heterologous antigens by vaccine strains. This is an antibiotic resistance-free maintenance system containing the asdA gene (essential for peptidoglycan synthesis) as a selectable marker to complement the lethal chromosomal DeltaasdA allele in live recombinant attenuated Salmonella vaccines (RASVs) such as Salmonella enterica serovar Typhimurium strain chi9447. pYA4534 harbors two origins of replication, pSC101 and pUC (low and high copy numbers, respectively). The pUC replication origin is controlled by a genetic switch formed by the operator/promoter of the P22 cro gene (O/P(cro)) (P(R)), which is negatively regulated by an arabinose-inducible P22 c2 gene located on both the plasmid and the chromosome (araC P(BAD) c2). The absence of arabinose, which is unavailable in vivo, triggers replication to a high-copy-number plasmid state. To validate these vector attributes, the Yersinia pestis virulence antigen LcrV was used to develop a vaccine against plague. An lcrV sequence encoding amino acids 131 to 326 (LcrV196) was optimized for expression in Salmonella, flanked with nucleotide sequences encoding the signal peptide (SS) and the carboxy-terminal domain (CT) of beta-lactamase, and cloned into pYA4534 under the control of the P(trc) promoter to generate plasmid pYA4535. Our results indicate that the live Salmonella vaccine strain chi9447 harboring pYA4535 efficiently stimulated a mixed Th1/Th2 immune response that protected mice against lethal challenge with Y. pestis strain CO92 introduced through either the intranasal or subcutaneous route.

The contribution of Toll-like receptor 2 to the innate recognition of a Leishmania infantum silent information regulator 2 protein

We have characterized a Leishmania protein belonging to the silent information regulator 2 (SIR2) family [SIR2 related protein 1 (SIR2RP1)] that might play an immunoregulatory role during infection through its capacity to trigger B-cell effector functions. We report here that SIR2RP1 leads to the proliferation of activated B cells, causing increased expression of major histocompatibility complex (MHC) II and the costimulatory molecules CD40 and CD86, which are critical ligands for T-cell cross-talk during the development of adaptive immune responses. In contrast, B cells isolated from Toll-like receptor 2 (TLR2) knockout mice were unable to respond to the SIR2RP1 stimulus. Similarly, SIR2RP1 induced the maturation of dendritic cells (DCs) in a TLR2-dependent manner with the secretion of pro-inflammatory cytokines [interleukin (IL)-12 and tumour necrosis factor (TNF)-alpha] and enhanced the costimulatory properties of DCs. Nevertheless, immunization assays demonstrated that TLR2-deficient mice were able to mount a specific humoral response to SIR2RP1. Interestingly, further investigations showed that macrophages were activated by SIR2RP1 even in the absence of TLR2. Therefore, a different type of interplay between SIR2RP1 and the major antigen-presenting cells in vivo could explain the immune response observed in TLR2-deficient mice. Together, these results demonstrate that TLR2 signalling contributes to SIR2RP1 recognition by innate immune host cells.

Comparative Analyses of Transcriptional Profiles in Mouse Organs Using a Pneumonic Plague Model after Infection with Wild-Type Yersinia pestis CO92 and Its Braun Lipoprotein Mutant

We employed Murine GeneChips to delineate the global transcriptional profiles of the livers, lungs, and spleens in a mouse pneumonic plague infection model with wild-type (WT) Y. pestis CO92 and its Braun lipoprotein (Δlpp) mutant with reduced virulence. These organs showed differential transcriptional responses to infection with WT Y. pestis, but the overall host functional processes affected were similar across all three tissues. Gene expression alterations were found in inflammation, cytokine signaling, and apoptotic cell death-associated genes. Comparison of WT and Δlpp mutant-infected mice indicated significant overlap in lipopolysaccharide- (LPS-) associated gene expression, but the absence of Lpp perturbed host cell signaling at critical regulatory junctions resulting in altered immune response and possibly host cell apoptosis. We generated a putative signaling pathway including major inflammatory components that could account for the synergistic action of LPS and Lpp and provided the mechanistic basis of attenuation caused by deletion of the lpp gene from Y. pestis in a mouse model of pneumonic plague.

Bordetella evades the host immune system by inducing IL-10 through a type III effector, BopN

The inflammatory response is one of several host alert mechanisms that recruit neutrophils from the circulation to the area of infection. We demonstrate that Bordetella, a bacterial pathogen, exploits an antiinflammatory cytokine, interleukin-10 (IL-10), to evade the host immune system. We identified a Bordetella effector, BopN, that is translocated into the host cell via the type III secretion system, where it induces enhanced production of IL-10. Interestingly, the BopN effector translocates itself into the nucleus and is involved in the down-regulation of mitogen-activated protein kinases. Using pharmacological blockade, we demonstrated that BopN-induced IL-10 production is mediated, at least in part, by its ability to block the extracellular signal-regulated kinase pathway. We also showed that BopN blocks nuclear translocation of nuclear factor κB p65 (NF-κBp65) but, in contrast, promotes nuclear translocation of NF-κBp50. A BopN-deficient strain was unable to induce IL-10 production in mice, resulting in the elimination of bacteria via neutrophil infiltration into the pulmonary alveoli. Furthermore, IL-10–deficient mice effectively eliminated wild-type as well as BopN mutant bacteria. Thus, Bordetella exploits BopN as a stealth strategy to shut off the host inflammatory reaction. These results explain the ability of Bordetella species to avoid induction of the inflammatory response.

Amino acid and structural variability of Yersinia pestis LcrV protein

The LcrV protein is a multifunctional virulence factor and protective antigen of the plague bacterium and is generally conserved between the epidemic strains of Yersinia pestis. We investigated the diversity in the LcrV sequences among non-epidemic Y. pestis strains which have a limited virulence in selected animal models and for humans. Sequencing of lcrV genes from 19 Y. pestis strains belonging to different phylogenetic groups (subspecies) showed that the LcrV proteins possess four major variable hotspots at positions 18, 72, 273, and 324-326. These major variations, together with other minor substitutions in amino acid sequences, allowed us to classify the LcrV alleles into five sequence types (A-E). We observed that the strains of different Y. pestis "subspecies" can have the same type of LcrV, including that conserved in epidemic strains, and different types of LcrV can exist within the same natural plague focus. Therefore, the phenomenon of "selective virulence" characteristic of the strains of the microtus biovar is unlikely to be the result of polymorphism of the V antigen. The LcrV polymorphisms were structurally analyzed by comparing the modeled structures of LcrV from all available strains. All changes except one occurred either in flexible regions or on the surface of the protein, but local chemical properties (i.e. those of a hydrophobic, hydrophilic, amphipathic, or charged nature) were conserved across all of the strains. Polymorphisms in flexible and surface regions are likely subject to less selective pressure, and have a limited impact on the structure. In contrast, the substitution of tryptophan at position 113 with either glutamic acid or glycine likely has a serious influence on the regional structure of the protein, and these mutations might have an effect on the function of LcrV. The polymorphisms at positions 18, 72 and 273 were accountable for differences in the oligomerization of LcrV.

N255 is a key residue for recognition by a monoclonal antibody which protects against Yersinia pestis infection

Mab7.3 to Yersinia pestis LcrV antigen (LcrV(Ype)) protected J774A.1 macrophages in vitro from killing by a Yersinia pseudotuberculosis strain expressing LcrV(Ype). Of 4 site-directed mutations in the coiled-coil region (148-169) and 7 mutations in the 225-255 sequence of LcrV(Ype), only the mutation of N255 to D255, abrogated the binding of Mab7.3 and reduced its protective capacity against plague. Since the Mab7.3 epitope in LcrV(Ype) (135-275) encompasses a region (136-180) thought to be exposed on the injectisome, we suggest that Mab7.3 protects by binding to LcrV(Ype) and interfering with protein-protein interactions necessary for type three secretion.

Oral vaccination with LcrV from Yersinia pestis KIM delivered by live attenuated Salmonella enterica serovar Typhimurium elicits a protective immune response against challenge with Yersinia pseudotuberculosis and Yersinia enterocolitica

The use of live recombinant attenuated Salmonella vaccines (RASV) synthesizing Yersinia proteins is a promising approach for controlling infection by Yersinia species. In this study, we constructed attenuated Salmonella strains which synthesize a truncated form of LcrV, LcrV196 and evaluated the immune response and protective efficacy elicited by these strains in mice against two other major species of Yersinia: Yersinia pseudotuberculosis and Yersinia enterocolitica. Surprisingly, we found that the RASV strain alone was sufficient to afford nearly full protection against challenge with Y. pseudotuberculosis, indicating the likelihood that Salmonella produces immunogenic cross-protective antigens. In contrast, lcrV196 expression was required for protection against challenge with Y. enterocolitica strain 8081, but was not sufficient to achieve significant protection against challenge with Y. enterocolitica strain WA, which expressed a divergent form of lcrV. Nevertheless, we are encouraged by these findings to continue pursuing our long-term goal of developing a single vaccine to protect against all three human pathogenic species of Yersinia.

Mapping of a microbial protein domain involved in binding and activation of the TLR2/TLR1 heterodimer

The pentameric B subunit of type IIb Escherichia coli enterotoxin (LT-IIb-B(5)), a doughnut-shaped oligomeric protein from enterotoxigenic E. coli, activates the TLR2/TLR1 heterodimer (TLR2/1). We investigated the molecular basis of the LT-IIb-B(5) interaction with TLR2/1 to define the structure-function relationship of LT-IIb-B(5) and, moreover, to gain an insight into how TLR2/1 recognizes large, nonacylated protein ligands that cannot fit within its lipid-binding pockets, as previously shown for the Pam(3)CysSerLys(4) (Pam(3)CSK(4)) lipopeptide. We first identified four critical residues in the upper region of the LT-IIb-B(5) pore. Corresponding point mutants (M69E, A70D, L73E, S74D) were defective in binding TLR2 or TLR1 and could not activate APCs, despite retaining full ganglioside-binding capacity. Point mutations in the TLR2/1 dimer interface, as determined in the crystallographic structure of the TLR2/1-Pam(3)CSK(4) complex, resulted in diminished activation by both Pam(3)CSK(4) and LT-IIb-B(5). Docking analysis of the LT-IIb-B(5) interaction with this apparently predominant activation conformation of TLR2/1 revealed that LT-IIb-B(5) might primarily contact the convex surface of the TLR2 central domain. Although the TLR1/LT-IIb-B(5) interface is relatively smaller, the leucine-rich repeat motifs 9-12 in the central domain of TLR1 were found to be critical for cooperative TLR2-induced cell activation by LT-IIb-B(5). Moreover, the putative LT-IIb-B(5) binding site overlaps partially with that of Pam(3)CSK(4); consistent with this, Pam(3)CSK(4) suppressed TLR2 binding of LT-IIb-B(5), albeit not as potently as self-competitive inhibition. We identified the upper pore region of LT-IIb-B(5) as a TLR2/1 interactive domain, which contacts the heterodimeric receptor at a site that is distinct from, although it overlaps with, that of Pam(3)CSK(4).

Outsmarting the host: bacteria modulating the immune response

Pathogenic bacteria and their hosts have had a two-way conversation for millions of years. This interaction has led to many measure/counter-measure responses by the host and bacteria. The host immune response has developed many mechanisms to neutralize and remove pathogen bacteria. In turn pathogenic bacteria have developed mechanisms to alter and evade the host immune response. We will review some of the mechanisms utilized by bacteria to accomplish this goal. We will also examine the current state of understanding of Francisella tularensis mediated immune evasion.

Yersinia enterocolitica Yop mutants as oral live carrier vaccines

Attenuated enteropathogenic yersiniae that translocate heterologous antigens into the cytosol of antigen presenting cells via their type three secretion system (TTSS) are considered promising candidates for the development of live oral vaccine carrier strains that induce CD8 T cell responses. Wild type Yersinia enterocolitica of serotype O:8 however efficiently suppresses the immune response of the host by translocating effector proteins called Yersinia outer proteins (Yops) into the cytosol of immune cells. We therefore tested immunogenicity, protective efficacy, and virulence ofyop mutants that translocate the model antigen Listeriolysin (LLO) of Listeria monocytogenes in a mouse model. A deltayopP mutant-based vaccine carrier strain induced the highest numbers of LLO91-99-specific CD8 T cells and effectively protected mice against a lethal challenge with Listeria whereas deltayopPT, deltayopPV(K42Q), and deltayopPO mutants of Y. enterocolitica induced fewer CD8 T cells and conferred only partial protection. The deltayopPH, deltayopPE, deltayopPM, and deltayopPQ mutants induced the weakest CD8 T cell response and did not significantly protect mice against Listeria presumably due to the strong attenuation of these strains in the mouse model. Even though a Y. enterocolitica strain WA-C(pTTSS), which translocated only LLO (but not Yops), induced superior MHC class I-restricted antigen presentation in DC compared to the deltayopP mutants in vitro, this strain was not able to significantly colonize mouse tissue or to induce CD8 T cell responses in vivo. The success in designing a Yersinia oral vaccine carrier is therefore dependent to a great extent on the subtle balance between immunogenicity and attenuation.

Exogenous Yersinia pestis quorum sensing molecules N-octanoyl-homoserine lactone and N-(3-oxooctanoyl)-homoserine lactone regulate the LcrV virulence factor

LcrV is a key Yersinia pestis antigen, immune regulator, and component of the type III secretion system (T3SS). Researchers have shown that N-acyl-homoserine lactones (AHLs) can down-regulate the expression of the LcrV homolog, PcrV, in Pseudomonas aeruginosa. Using ELISA, western blot, DNA microarray analysis, and real time PCR we demonstrate that the addition of AHL molecules N-octanoyl-homoserine lactone (C8) or N-(3-oxooctanoyl)-homoserine lactone (oxo-C8) to Y. pestis cultures down-regulates LcrV protein expression. DNA microarray analysis shows 10 additional T3SS genes are consistently down-regulated by C8 or oxo-C8. This is the first report demonstrating that AHLs regulate Y. pestis virulence factor expression.

CpG oligodeoxynucleotides augment the murine immune response to the Yersinia pestis F1-V vaccine in bubonic and pneumonic models of plague

The current U.S. Department of Defense candidate plague vaccine is a fusion between two Yersinia pestis proteins: the F1 capsular protein, and the low calcium response (Lcr) V-protein. We hypothesized that an immunomodulator, such as CpG oligodeoxynucleotide (ODN)s, could augment the immune response to the plague F1-V vaccine in a mouse model for plague. CpG ODNs significantly augmented the antibody response and efficacy of a single dose of the plague vaccine in murine bubonic and pneumonic models of plague. In the latter study, we also found an overall significant augmentation the immune response to the individual subunits of the plague vaccine by CpG ODN 2006. In a long-term, prime-boost study, CpG ODN induced a significant early augmentation of the IgG response to the vaccine. The presence of CpG ODN induced a significant increase in the IgG2a subclass response to the vaccine up to 5 months after the boost. Our studies showed that CpG ODNs significantly augmented the IgG antibody response to the plague vaccine, which increased the probability of survival in murine models of plague (P<0.0001).

Induction of innate immune response through TLR2 and dectin 1 prevents type 1 diabetes

Studies have suggested a correlation between the decline in infectious diseases and increase in the incidence of type 1 diabetes (T1D) in developed countries. Pathogens influence the disease outcome through innate immune receptors such as TLRs. Here we report the effect of ligation of TLR2 and dectin 1 on APCs and the influence of innate immune response induced through these receptors on T1D. Exposure of APCs of NOD mice to zymosan, a fungal cell wall component that interacts with TLR2 and dectin 1, resulted in the release of significant amounts of IL-10, TGF-beta1, IL-2, and TNF-alpha. Treatment of pre- and early hyperglycemic mice with zymosan resulted in suppression of insulitis, leading to a significant delay in hyperglycemia. T cells from zymosan-treated mice showed reduced ability to induce diabetes in NOD-Scid mice compared with control T cells. Zymosan treatment induced suppression of T1D was associated with an increase in the L-selectin(high) T cell frequencies and enhanced suppressor function of CD4(+)CD25(+) T regulatory cells. Further, activation by anti-CD3-Ab induced larger amounts of TGF-beta1 and/or IL-10 production by CD4(+)CD25(+) and CD4(+)CD25(-) T cells from zymosan-treated mice. These results show that innate immune response through TLR2 and dectin 1 results in suppressor cytokine production by APCs and promotes the regulatory function of T cells. Our study demonstrates the possible involvement of signaling through innate immune receptors such as TLR2 and dectin 1 in reduced T1D incidence under the conditions of low hygiene, and the potential of targeting them for treating T1D.

Substrains of 129 mice are resistant to Yersinia pestis KIM5: implications for interleukin-10-deficient mice

Interleukin-10 (IL-10)-deficient mice are resistant to several pathogens, including Yersinia pestis. Surprisingly, we observed that heterozygous IL-10(+/-) mice also survive high-dose intravenous infection with Y. pestis KIM5 (Pgm(-)). Analysis of commercial IL-10(-/-) mice revealed that at least 30 cM of genomic DNA from the original 129 strain remains, including a functional Slc11a1 (Nramp1) gene. Interestingly, two substrains of 129 mice were resistant to high-dose Y. pestis KIM5. Resistance does not appear to be recessive, as F(1) mice (C57BL/6J x 129) also survived a high-dose challenge. A QTL-based genetic scan of chromosome 1 with 35 infected F(1) backcrossed mice revealed that resistance to KIM5 maps to a region near IL-10. Two novel IL-10(+/+) mouse strains which each possess most of the original 30-cM stretch of 129 DNA maintained resistance to high-dose infection with Y. pestis KIM5 even in a heterozygous state. Conversely, a novel IL-10(-/-) mouse strain in which most of the 129 DNA has been crossed out exhibited intermediate resistance to KIM5, while the corresponding IL-10(+/-) strain was completely susceptible. Taken together, these results demonstrate that 129-derived genomic DNA near IL-10 confers resistance to Yersinia pestis KIM5 and contributes to the observed resistance of IL-10(-/-) mice.

Toll gates to periodontal host modulation and vaccine therapy

Toll-like receptors (TLRs) are central mediators of innate antimicrobial and inflammatory responses and play instructive roles in the development of the adaptive immune response. Thus when stimulated by certain agonists, TLRs serve as adjuvant receptors that link innate and adaptive immunity. However, when excessively activated or inadequately controlled during an infection, TLRs may contribute to immunopathology associated with inflammatory diseases, such as periodontitis. Moreover, certain microbial pathogens appear to exploit aspects of TLR signalling in ways that enhance their adaptive fitness. The diverse and important roles played by TLRs suggest that therapeutic manipulation of TLR signalling may have implications in the control of infection, attenuation of inflammation, and the development of vaccine adjuvants for the treatment of periodontitis. Successful application of TLR-based therapeutic modalities in periodontitis would require highly selective and precisely targeted intervention. This would in turn necessitate precise characterization of TLR signalling pathways in response to periodontal pathogens, as well as development of effective and specific agonists or antagonists of TLR function and signalling. This review summarizes the current status of TLR biology as it relates to periodontitis, and evaluates the potential of TLR-based approaches for host-modulation therapy in this oral disease.

Toll-like receptor 6 drives differentiation of tolerogenic dendritic cells and contributes to LcrV-mediated plague pathogenesis

Educating dendritic cells (DC) to become tolerogenic DC, which promote regulatory IL-10 immune responses, represents an effective immune evasion strategy for pathogens. Yersinia pestis virulence factor LcrV is reported to induce IL-10 production via interaction with Toll-like receptor (TLR) 2. However, TLR2-/- mice are not protected against subcutaneous plague infection. Using complementary in vitro and in vivo approaches and LcrV as a model, we show that TLR6 associates with TLR2 to induce tolerogenic DC and regulatory type-1 T cells selectively secreting IL-10. In contrast, TLR1 heterodimerizes with TLR2 to promote proinflammatory IL-12p40 cytokine, producing DC and inflammatory T cell differentiation. LcrV specifically hijacks the TLR2/6 pathway to stimulate IL-10 production, which blocks host protective inflammatory responses. These results explain why TLR2 can mediate both pro- and anti-inflammatory responses and identify TLR6 as a distinct receptor driving regulatory IL-10 responses.

Immune defense against pneumonic plague

SUMMARY

Yersinia pestis is one of the world's most virulent human pathogens. Inhalation of this Gram-negative bacterium causes pneumonic plague, a rapidly progressing and usually fatal disease. Extensively antibiotic-resistant strains of Y. pestis exist and have significant potential for exploitation as agents of terrorism and biowarfare. Subunit vaccines comprised of the Y. pestis F1 and LcrV proteins are well-tolerated and immunogenic in humans but cannot be tested for efficacy, because pneumonic plague outbreaks are uncommon and intentional infection of humans is unethical. In animal models, F1/LcrV-based vaccines protect mice and cynomolgus macaques but have failed, thus far, to adequately protect African green monkeys. We lack an explanation for this inconsistent efficacy. We also lack reliable correlate assays for protective immunity. These deficiencies are hampering efforts to improve vaccine efficacy. Here, I review the immunology of pneumonic plague, focusing on evidence that humoral and cellular defense mechanisms collaborate to defend against pulmonary Y. pestis infection.

Role of IFN-gamma and IL-6 in a protective immune response to Yersinia enterocolitica in mice

Background

Yersinia outer protein (Yop) H is a secreted virulence factor of Yersinia enterocolitica (Ye), which inhibits phagocytosis of Ye and contributes to the virulence of Ye in mice. The aim of this study was to address whether and how YopH affects the innate immune response to Ye in mice.

Results

For this purpose, mice were infected with wild type Ye (pYV⁺) or a YopH-deficient Ye mutant strain (ΔyopH). CD11b⁺ cells were isolated from the infected spleen and subjected to gene expression analysis using microarrays. Despite the attenuation of ΔyopH in vivo, by variation of infection doses we were able to achieve conditions that allow comparison of gene expression in pYV⁺ and ΔyopH infection, using either comparable infection courses or splenic bacterial burden. Gene expression analysis provided evidence that expression levels of several immune response genes, including IFN-γ and IL-6, are high after pYV⁺ infection but low after sublethal ΔyopH infection. In line with these findings, infection of IFN-γR^-/- and IL-6^-/- mice with pYV⁺ or ΔyopH revealed that these cytokines are not necessarily required for control of ΔyopH, but are essential for defense against infection with the more virulent pYV⁺. Consistently, IFN-γ pretreatment of bone marrow derived macrophages (BMDM) strongly enhanced their ability in killing intracellular Ye bacteria.

Conclusion

In conclusion, this data suggests that IFN-γ-mediated effector mechanisms can partially compensate virulence exerted by YopH. These results shed new light on the protective role of IFN-γ in Ye wild type infections.