Pertussis toxin targets the innate immunity through DAP12, FcRγ, and MyD88 adaptor proteins.

Activation of the innate immunity by adjuvants, such as pertussis toxin (PTX), in the presence of autoreactive lymphocytes and antigen mimicry is sufficient to trigger autoimmunity. Toll-like, C-type lectin, and immunglobulin-like receptors play an important role in the innate immunity by sensing a variety of microbial products through several adaptor proteins, including MyD88, DAP12, and FcRγ. This study investigated the interaction between PTX and innate immune components. The direct interactions between coated PTX and receptor-fusion proteins were examined using ELISA-based binding assays. Functionally, PTX-binding receptors could be classified into two groups: inhibition (DAP12-coupled TREM2, ITIM-bearing SIRPα, SIGNR1/SIGNR3/DCSIGN) and activation (MyD88-associated TLR4, DAP12-coupled LMIR5/CD300b, FcRγ-coupled LMIR8/CD300c, CLEC9A, MGL-1). DAP12, MyD88, and FcRγ were selected for further investigation. A comprehensive analysis of gene transcription showed that PTX up-regulated the expression of various inflammatory mediators. DAP12 deficiency resulted in reduction or enhancement of inflammatory responses in a cytokine-specific manner. PTX was able to activate the TREM2-DAP12 signalling pathway. PTX induced lower expression of inflammatory mediators in the absence of FcRγ alone and substantially lost its inflammatory capacity in the absence of both FcRγ and MyD88. PTX was able to activate the MyD88-NF-κB signalling pathway in the presence of TLR2 or TLR4. The inflammatory activity of PTX was completely lost by heating. These results demonstrate that PTX targets the innate immunity through DAP12, FcRγ, and MyD88 providing new insights into the immunobiology of PTX.

The immunobiology of Campylobacter jejuni: Innate immunity and autoimmune diseases.

The Gram-negative bacterium Campylobacter jejuni causes gastroenteritis and Guillain-Barré syndrome in humans. Recent advances in the immunobiology of C. jejuni have been made. This review summarizes C. jejuni-binding innate receptors and highlights the role of innate immunity in autoimmune diseases. This human pathogen produces a variety of glycoconjugates, including human ganglioside-like determinants and multiple activators of Toll-like receptors (TLRs). Furthermore, C. jejuni targets MyD88, NLRP3 inflammasome, TIR-domain-containing adapter-inducing interferon-ß (TRIF), sialic acid-binding immunoglobulin-like lectins (Siglecs), macrophage galactose-type lectin (MGL), and immunoglobulin-like receptors (TREM2, LMIR5/CD300b). The roles of these innate receptors and signaling molecules have been extensively studied. MyD88-mediated TLR activation or inflammasome-dependent IL-1ß secretion is essential for autoimmune induction. TRIF mediates the production of type I interferons that promote humoral immune responses and immunoglobulin class-switching. Siglec-1 and Siglec-7 interact directly with gangliosides. Siglec-1 activation enhances phagocytosis and inflammatory responses. MGL internalizes GalNAc-containing glycoconjugates. TREM2 is well-known for its role in phagocytosis. LMIR5 recognizes C. jejuni components and endogenous sulfoglycolipids. Several lines of evidence from animal models of autoimmune diseases suggest that simultaneous activation of innate immunity in the presence of autoreactive lymphocytes or antigen mimicry may link C. jejuni to immunopathology.

Evidence for TLR4 and FcRγ-CARD9 activation by cholera toxin B subunit and its direct bindings to TREM2 and LMIR5 receptors.

Cholera toxin (CTX) is a virulent factor of Vibrio cholerae that causes life-threatening diarrheal disease. Its non-toxic subunit CTB has been extensively studied for vaccine delivery. In immune cells, CTB induces a number of signaling molecules related to cellular activation and cytokine production. The mechanisms by which CTB exerts its immunological effects are not understood. We report here the immunological targets of CTB. The unexpected finding that GM1 ganglioside inhibited NF-κB activation in human monocytes stimulated with CTX and agonists of Toll-like receptors (TLR) suggests the possibility of CTX-TLR interaction. Indeed, CTX-induced IL-6 production was substantially reduced in MyD88(-/-) or TLR4(-/-) macrophages. Ectopic expression of TLR4 was required for CTX-induced NF-κB activation in HEK 293 cells. Furthermore, the inflammatory capacity of CTB was lost in the absence of TLR4, adaptor protein FcRγ, or its downstream signaling molecule CARD9. Attempts have been made to identify CTB-binding targets from various C-type lectin and immunoglobulin-like receptors. CTB targeted not only GM1 and TLR4 but also TREM2 and LMIR5/CD300b. CTB-TREM2 interaction initiated signal transduction through adaptor protein DAP12. The binding of CTB inhibited LMIR5 activation induced by its endogenous ligand 3-O-sulfo-ß-d-galactosylceramide C24:1. In summary, CTB targets TLR4, FcRγ-CARD9, TREM2, and LMIR5. These findings provide new insights into the immunobiology of cholera toxin.

Campylobacter jejuni targets immunoglobulin-like receptor LMIR5.

Campylobacter jejuni causes gastroenteritis and Guillain-Barré syndrome. Host immunity plays an important role in the disease pathogenesis; however, little is known about the immune receptors for C. jejuni. We report here that C. jejuni targets C-type lectin (SIGNR1, SIGNR3) and immunoglobulin-like receptors (TREM2, TREM3, LMIR5, LMIR8). Among these, C. jejuni interacted preferentially with LMIR5, which was selected for further verification using reporter cells. LMIR5 ligation by C. jejuni activated transcriptional factor NFAT through adaptor protein DAP12. Furthermore, LMIR5 activators were identified as protein components, RNA-associated proteins, and 150-kDa high-molecular-weight glycoconjugates. This finding discloses potential receptors that might link C. jejuni to immunopathology.

3-O-sulfo-ß-D-galactose moiety of endogenous sulfoglycolipids is a potential ligand for immunoglobulin-like receptor LMIR5.

Axonal Guillain-Barré syndrome (GBS) is an autoimmune neuropathy characterized by limb weakness and/or paralysis due to the presence of autoantibodies against brain glycolipids. The immune receptors that recognize these autoimmune targets have not been described. In this study, 12 C-type lectin and 10 immunoglobulin-like receptors were screened for their potential ligands from the brain glycolipids, which are the binding targets for GBS autoantibodies. These glycolipids were GM1, GM2, GD1a, GD1b, GQ1b, crude gangliosides, and 3-O-sulfo-ß-D-galactosylceramide C24:1 (designated as C24:1). A direct interaction between ligand and receptor was examined using an ELISA-based binding assay. C-type lectin (CLEC5a, SIGNR3) and immunoglobulin-like receptors (TREM2, TREM3, LMIR2, LMIR5, LMIR7, LMIR8) interacted with C24:1. In addition, TREM3 did bind to GQ1b. LMIR5 interacted with GD1a, GQ1b, and crude gangliosides. Binding with highest affinity was observed for the LMIR5-C24:1 interaction, which was selected for further verification. C24:1 was found to induce MCP-1 production, but not proinflammatory cytokines, in basophils. C24:1-induced MCP-1 production was significantly reduced in DAP12(-/-) basophils. Importantly, LMIR5 ligation by C24:1 resulted in NFAT activation through DAP12 in LMIR5-expressing reporter cells. Structural analysis showed that LMIR5 recognized the 3-O-sulfo-ß-D-galactose moiety of C24:1. The findings indicated that C24:1 is a potential ligand for DAP12-coupled LMIR5.

Toll-like receptors recognize distinct proteinase-resistant glycoconjugates in Campylobacter jejuni and Escherichia coli.

Campylobacter jejuni causes gastroenteritis and autoimmune neuropathy Guillain-Barré syndrome. The mechanism by which C. jejuni infection results in such the hyperimmunity is not completely understood. Host immunity plays an important role in the disease pathogenesis; however, little is known how immune system recognizes this human pathogen. In this study, we report that Toll-like receptors recognize distinct proteinase K-resistant glycoconjugates in C. jejuni and Escherichia coli. Lipopolysaccharide is solely proteinase-resistant glycoconjugate in E. coli. In contrast, C. jejuni possesses at least five different components that are resistant to proteinase digestion and are capable of inducing NF-κB activation through TLR2 and TLR4. Possession of multiple activators of Toll-like receptors may be the unique strategy of C. jejuni to trigger hyperimmunity.

LMIR5 extracellular domain activates myeloid cells through toll-like receptor 4.

LMIR5/CD300b is an activating immunoglobulin-like receptor whose extracellular domain (LMIR5-Fc) is constitutively released from immune cells. The release of LMIR5-Fc is augmented upon stimulation with TLR agonists. LMIR5-Fc is reported to possess inflammatory activity and amplify LPS-induced lethal inflammation; however, its action mechanism has not been clarified. This study was aimed to identify receptors for LMIR5-Fc. Using NF-κB reporter cells in human monocytes THP1, LMIR5-Fc was solely found to trigger NF-κB activation among various signaling receptors examined. In addition, an injection of LMIR5-Fc into the mouse peritoneal resulted in a rapid production of inflammatory mediators and an amplification of LPS activity. Moreover, LMIR5-Fc-induced cytokine production was markedly reduced in TLR4-deficient mouse macrophages. Using TLR4 reporter cells, the LMIR5-Fc sample that contained a trace amount of endotoxin under the sensitivity of reporter cells triggered a potent NF-κB activation. Furthermore, the inflammatory activity of LMIR5-Fc was completely lost by heating but unchanged by polymyxin B pretreatment. Using TLR4 fusion protein, TLR4 was found to interact specifically with LMIR5-overexpressing cells. Therefore, LMIR5-Fc is new inflammatory mediator and endogenous ligand of TLR4. This study provides an insight into the positive feedback mechanism of inflammation through TLR4-LMIR5-Fc axis.

Complement inhibitor prevents disruption of sodium channel clusters in a rabbit model of Guillain-Barré syndrome.

Complement-mediated disruption of voltage-gated sodium channels at the nodes of Ranvier acts in the development of acute motor axonal neuropathy. Nafamostat mesilate, a synthetic serine protease inhibitor, used in clinical practice for more than 20 years, has anti-complement activity. Acute motor axonal neuropathy rabbits obtained by GM1 ganglioside sensitization were or were not given nafamostat mesilate intravenously. Complement deposition and sodium channel disruption in the spinal anterior roots were significantly less frequent in the treated rabbits than in the controls. Nafamostat mesilate inhibited complement deposition and prevented sodium channel disruption. This provided the rationale for a clinical trial.

Evaluation of a cytolethal distending toxin (cdt) gene-based species-specific multiplex PCR assay for the identification of Campylobacter strains isolated from poultry in Thailand.

We have recently developed a cytolethal distending toxin (cdt) gene-based species-specific multiplex PCR assay for identifying Campylobacter jejuni, C. coli and C. fetus. In the present study, the applicability of this assay was evaluated with 34 Campylobacter-like organisms isolated from poultry in Thailand for species identification and was compared with other assays including API Campy, 16S rRNA gene sequence, and hippuricase (hipO) gene detection. Of the 34 strains analyzed, 20, 10 and 1 were identified as C. jejuni, C. coli, and Arcobacter cryaerophilus, respectively, and 3 could not be identified by API Campy. However, 16S rRNA gene analysis, showed that all 34 strains are C. jejuni/coli. To discriminate between these 2 species, the hipO gene, which is specifically present in C. jejuni, was examined by PCR and was detected in 20 strains, which were identified as C. jejuni by API Campy but not in the remaining 14 strains. Collective results indicated that 20 strains were C. jejuni whereas the 14 strains were C. coli. When the cdt gene-based multiplex PCR was employed, however, 19, 20 and 19 strains were identified as C. jejuni while 13, 14 and 13 were identified as C. coli by the cdtA, cdtB and cdtC gene-based multiplex PCR, respectively. Pulsed-field gel electrophoresis revealed that C. jejuni and C. coli strains analyzed are genetically diverse. Taken together, these data suggest that the cdt gene-based multiplex PCR, particularly cdtB gene-based multiplex PCR, is a simple, rapid and reliable method for identifying the species of Campylobacter strains.

Bidirectional transcription of lipooligosaccharide synthesis genes from Campylobacter jejuni.

The lipooligosaccharide (LOS) molecules of Campylobacter jejuni are involved in virulence and induction of the Guillain-Barré syndrome (GBS). This study analysed the transcription of the LOS synthesis genes from the GBS-inducing C. jejuni strain HB 93-13 under microaerobic conditions. Fourteen consecutive genes Cj1132c, waaC, htrB, wlaNC, wlaND, cgtA, cgtB, cstII, neuB, neuC, neuA, wlaVA, wlaQA, and waaF were included. The results of rapid amplification of cDNA ends and single-stranded ligation of complementary ends showed initiation sites with potential promoter regions on both DNA strands in the Cj1132c/waaC, cgtB/cstII, and wlaQA/waaF strand-switch regions. Other termini without recognisable promoter region were also found throughout the LOS gene cluster, suggesting a low specificity of the polymerase during transcription. In addition, all gene junction regions were cloned into the shuttle vector pMW10 carrying the promoterless lacZ gene to identify functional promoter sites. Bidirectional active promoters were found in the strand-switch regions. The results of RT-PCR and cDNA blotting indicated that transcriptional linkage occurred between different operons, indicating a lack of transcription termination within the LOS gene cluster. Moreover, the results of semi-quantitative RT-PCR and real-time RT-PCR showed that both DNA strands were transcribed but transcription of the coding strand was at a higher rate. The results presented here provide an insight into transcription of the LOS synthesis gene cluster of C. jejuni.

Evaluation of eight RNA isolation methods for transcriptional analysis in Campylobacter jejuni.

DNA-free RNA samples are essential to investigate gene regulation using real-time RT-PCR. This study evaluated eight RNA isolation methods in combination with TURBO DNase treatment and acid phenol extractions for their ability to produce DNA-free RNA from Campylobacter jejuni strains.

Expression of the htrB gene is essential for responsiveness of Salmonella typhimurium and Campylobacter jejuni to harsh environments.

In Campylobacter jejuni, an htrB homologous gene is located in the lipo-oligosaccharide synthesis gene cluster. This study examined the effects of htrB expression on the responsiveness of Salmonella typhimurium and C. jejuni to harsh environments. Complementation experiments showed that the C. jejuni htrB gene could restore the normal morphology of the Salmonella htrB mutant, and its ability to grow without inhibition under heat, acid and osmotic stresses, but not bile stress. This indicated that the htrB genes in C. jejuni and S. typhimurium exhibit similar pleiotropic effects. Moreover, quantitative real-time RT-PCR showed that expression of the C. jejuni htrB gene was upregulated under acid, heat, oxidative and osmotic stresses, but did not change under bile stress. This indicated that the C. jejuni htrB gene plays a role in regulating cell responses to various environmental changes. Furthermore, deletion mutation of the htrB gene in C. jejuni was lethal, indicating that the htrB gene is essential for C. jejuni survival. Therefore, these results showed that expression of the htrB gene is essential for the response of S. typhimurium and C. jejuni to environmental stresses.

Exchange of lipooligosaccharide synthesis genes creates potential Guillain-Barre syndrome-inducible strains of Campylobacter jejuni.

Human ganglioside-like structures, such as GM1, found on some Campylobacter jejuni strains have been linked to inducing the Guillain-Barré Syndrome (GBS). This study shows that a C. jejuni strain without GM1-like molecules acquired large DNA fragments, including lipooligosaccharide synthesis genes, from a strain expressing GM1-like molecules and consequently transformed into a number of potential GBS-inducible transformants, which exhibited a high degree of genetic and phenotypic diversity.