The negative regulation of Toll‐like receptor and associated pathways

Toll-interacting protein is activated by the transcription factor GATA1 and Sp1 to negatively regulate NF-κB and MAPK pathways in the Japanese eel (Anguilla japonica)

Toll-interacting protein (Tollip) serves as a crucial inhibitory factor in the modulation of Toll-like receptor (TLR)-mediated innate immunological responses. The structure and function of Tollip have been well documented in mammals, yet the information in teleost remained limited. This work employed in vitro overexpression and RNA interference in vivo and in vitro to comprehensively examine the regulatory effects of AjTollip on NF-κB and MAPK signaling pathways. The levels of p65, c-Fos, c-Jun, IL-1, IL-6, and TNF-α were dramatically reduced following overexpression of AjTollip, whereas knocking down AjTollip in vivo and in vitro enhanced those genes' expression. Protein molecular docking simulations showed AjTollip interacts with AjTLR2, AjIRAK4a, and AjIRAK4b. A better understanding of the transcriptional regulation of AjTollip is crucial to elucidating the role of Tollip in fish antibacterial response. Herein, we cloned and characterized a 2.2 kb AjTollip gene promoter sequence. The transcription factors GATA1 and Sp1 were determined to be associated with the activation of AjTollip expression by using promoter truncation and targeted mutagenesis techniques. Collectively, our results indicate that AjTollip suppresses the NF-κB and MAPK signaling pathways, leading to the decreased expression of the downstream inflammatory factors, and GATA1 and Sp1 play a vital role in regulating AjTollip expression.

Effects of zinc supplementation and implant abscess on the immune system and growth performance of growing beef steers

Seventy-two Angus-cross steers (261 ± 14 kg) were utilized to determine the effects of supplemental Zn sulfate on growth, trace mineral status, circulating immune cells, and functional innate immune responses. Steers were stratified by weight and implanted with a Component E-S with Tylan implant (Elanco Animal Health, Greenfield, IN) on day 0. Dietary treatments included: control (CON; no supplemental Zn), Zn100 (100 mg supplemental Zn/kg DM), and Zn150 (150 mg supplemental Zn/kg DM). Analyzed dietary concentrations of Zn were 58, 160, and 207 mg Zn/kg DM, respectively. On days 13 and 57, blood from nine steers per treatment was collected for immune analyses (cell phenotyping and response to stimulus). On day 16, implant abscesses were evaluated by palpation and visual appraisal. Sixty percent of steers had abscesses; however, there were no differences in abscess prevalence due to treatment (P = 0.67). Data were analyzed as a split-plot design using the Mixed procedure of SAS 9.4 (Cary, NC) with effects of dietary treatment, abscess, and their interaction. There was a tendency (treatment × abscess; P ≤ 0.09) for steers without abscesses to have greater average daily gain (ADG; treatment × abscess P = 0.06) and gain:feed (G:F; treatment × abscess P = 0.09) from d 14 to 27 in CON and Zn100 while within Zn150 steers without abscesses tended to have lesser ADG and G:F than abscessed steers. There were no other treatment × abscess effects for growth performance, but steers with abscesses tended to have decreased final body weight (P = 0.10) and overall G:F (days 0 to 57; P = 0.08). There was no interaction of treatment and abscess on immune cell populations on days 13 or 58 (treatment × abscess P ≥ 0.11). On day 13, Zn150 steers had increased CD45RO + gamma delta (P = 0.04) T cells. Abscessed steers had increased CD21 + B cells (P = 0.03) and tended to have increased CD21 + (P = 0.07) and CD21 + MHCIIhi (P = 0.07) B cells in circulation. This study shows zinc supplementation and implant abscesses can alter the immune system and growth performance of growing beef steers.

Salmonellosis: An Overview of Epidemiology, Pathogenesis, and Innovative Approaches to Mitigate the Antimicrobial Resistant Infections

Salmonella is a major foodborne pathogen and a leading cause of gastroenteritis in humans and animals. Salmonella is highly pathogenic and encompasses more than 2600 characterized serovars. The transmission of Salmonella to humans occurs through the farm-to-fork continuum and is commonly linked to the consumption of animal-derived food products. Among these sources, poultry and poultry products are primary contributors, followed by beef, pork, fish, and non-animal-derived food such as fruits and vegetables. While antibiotics constitute the primary treatment for salmonellosis, the emergence of antibiotic resistance and the rise of multidrug-resistant (MDR) Salmonella strains have highlighted the urgency of developing antibiotic alternatives. Effective infection management necessitates a comprehensive understanding of the pathogen's epidemiology and transmission dynamics. Therefore, this comprehensive review focuses on the epidemiology, sources of infection, risk factors, transmission dynamics, and the host range of Salmonella serotypes. This review also investigates the disease characteristics observed in both humans and animals, antibiotic resistance, pathogenesis, and potential strategies for treatment and control of salmonellosis, emphasizing the most recent antibiotic-alternative approaches for infection control.

Gcm counteracts Toll-induced inflammation and impacts hemocyte number through cholinergic signaling

Hemocytes, the myeloid-like immune cells of Drosophila, fulfill a variety of functions that are not completely understood, ranging from phagocytosis to transduction of inflammatory signals. We here show that downregulating the hemocyte-specific Glial cell deficient/Glial cell missing (Glide/Gcm) transcription factor enhances the inflammatory response to the constitutive activation of the Toll pathway. This correlates with lower levels of glutathione S-transferase, suggesting an implication of Glide/Gcm in reactive oxygen species (ROS) signaling and calling for a widespread anti-inflammatory potential of Glide/Gcm. In addition, our data reveal the expression of acetylcholine receptors in hemocytes and that Toll activation affects their expressions, disclosing a novel aspect of the inflammatory response mediated by neurotransmitters. Finally, we provide evidence for acetylcholine receptor nicotinic acetylcholine receptor alpha 6 (nAchRalpha6) regulating hemocyte proliferation in a cell autonomous fashion and for non-cell autonomous cholinergic signaling regulating the number of hemocytes. Altogether, this study provides new insights on the molecular pathways involved in the inflammatory response.

Toll-interacting protein participates in immunity and development of the lepidopteran insect Antheraea pernyi

Toll-interacting protein (Tollip) participates in multiple biological processes. However, the biological functions of Tollip proteins in insects remain to be further explored. Here, the genomic sequence of tollip gene from Antheraea pernyi (named Ap-Tollip) was identified with a length of 15,060 bp, including eight exons and seven introns. The predicted Ap-Tollip protein contained conserved C2 and CUE domains and was highly homologous to those tollips from invertebrates. Ap-Tollip was highly expressed in fat body compared with other determined tissues. As far as the developmental stages were concerned, the highest expression level was found at the 14th day in eggs or the 3rd day of the 1st instar. Ap-Tollip was also obviously regulated by lipopolysaccharide, polycytidylic acid or 20E in different tissues. In addition, the interaction between Ap-Tollip and ubiquitin was confirmed by western blotting and pull-down assay. RNAi of Ap-Tollip significantly affected the expression levels of apoptosis and autophagy-related genes. These results indicated that Ap-Tollip was involved in immunity and development of A. pernyi.

Secreted Akkermansia muciniphila threonyl-tRNA synthetase functions to monitor and modulate immune homeostasis

Commensal bacteria are critically involved in the establishment of tolerance against inflammatory challenges, the molecular mechanisms of which are just being uncovered. All kingdoms of life produce aminoacyl-tRNA synthetases (ARSs). Thus far, the non-translational roles of ARSs have largely been reported in eukaryotes. Here, we report that the threonyl-tRNA synthetase (AmTARS) of the gut-associated bacterium Akkermansia muciniphila is secreted and functions to monitor and modulate immune homeostasis. Secreted AmTARS triggers M2 macrophage polarization and orchestrates the production of anti-inflammatory IL-10 via its unique, evolutionary-acquired regions, which mediates specific interactions with TLR2. This interaction activates the MAPK and PI3K/AKT signaling pathways, which converge on CREB, leading to an efficient production of IL-10 and suppression of the central inflammatory mediator NF-κB. AmTARS restores IL-10-positive macrophages, increases IL-10 levels in the serum, and attenuates the pathological effects in colitis mice. Thus, commensal tRNA synthetases can act as intrinsic mediators that maintain homeostasis.

A review on gout: Looking back and looking ahead

Gout is a metabolic disease caused by the deposition of monosodium urate (MSU) crystals inside joints, which leads to inflammation and tissue damage. Increased concentration of serum urate is an essential step in the development of gout. Serum urate is regulated by urate transporters in the kidney and intestine, especially GLUT9 (SLC2A9), URAT1 (SLC22A12) and ABCG. Activation of NLRP3 inflammasome bodies and subsequent release of IL-1β by monosodium urate crystals induce the crescendo of acute gouty arthritis, while neutrophil extracellular traps (NETs) are considered to drive the self-resolving of gout within a few days. If untreated, acute gout may eventually develop into chronic tophaceous gout characterized by tophi, chronic gouty synovitis, and structural joint damage, leading the crushing burden of treatment. Although the research on the pathological mechanism of gout has been gradually deepened in recent years, many clinical manifestations of gout are still unable to be fully elucidated. Here, we reviewed the molecular pathological mechanism behind various clinical manifestations of gout, with a view to making contributions to further understanding and treatment.

A TMEM16J variant leads to dysregulated cytosolic calcium which may lead to renal disease

SIGIRR (single immunoglobulin IL-1 related receptor), PKP3 (plakophilin 3), and TMEM16J (anoctamin 9), a putative calcium-activated ion channel and phospholipid scramblase, control the immune response and the extent of inflammation. Variants of SIGIRR/PKP3/TMEM16J lead to severe inflammatory diseases such as pneumonia, enterocolitis, and kidney graft rejection. Meta-analysis of genome-wide association studies identified TMEM16J-T604A as a promotor for chronic kidney disease (CKD), but the disease mechanism and function of TMEM16J remain unknown. Here, we demonstrate TMEM16J as a calcium-activated calcium-permeable channel, which is expressed in the endoplasmic reticulum (ER). TMEM16J controls the intracellular distribution of calcium, and inhibits intracellular receptor-mediated Ca²⁺ signals and Ca²⁺ -dependent activation of ion channels, but augments transcription and release of pro-inflammatory cytokines. Renal epithelial cells expressing the variant TMEM16J-T604A show enhanced calcium signals when compared to cells expressing wt-TMEM16J, and demonstrate spontaneous transcription and release of cytokines. This study identifies TMEM16J as an important regulator of intracellular Ca²⁺ signals, ion channel activity, and cytokine release. TMEM16J may therefore affect immune response in renal tissue and immune cells.

Stress signaling and STAT1 activation characterize the keratinocytic gene expression pattern in Hidradenitis suppurativa

BACKGROUND

The pathogenetic factors generating the innate immune signal necessary for T cell activation, initiation and chronification of Hidradenitis suppurativa (HS, also known as Acne inversa) are still poorly understood. Emerging evidence suggests that a defective keratinocyte function critically contributes to HS disease development and progression.

OBJECTIVES

To elucidate the role of keratinocytes in HS lesion formation, we compared the transcriptomes of lesional and perilesional epidermis isolated from HS patients by RNA sequencing (RNA Seq).

METHODS

Pairwise-matched lesional and perilesional HS skin samples of five different donors were obtained and epidermal keratinocytes freshly isolated and processed for RNA extraction and RNA seq. Lesionally regulated genes were analyzed by large scale promotor analysis and functional annotation clustering to identify epidermally overrepresented transcription factor binding sites and functionally related gene groups. Results were experimentally validated with independent epidermal isolates of patient-matched lesional and perilesional HS skin employing qRT-PCR, cell culture, immunoblot, and immunostaining.

RESULTS

We show that HS is characterized by a strong epidermal stress state evident by a significant overrepresentation of an AP-1-driven gene signature and a substantial activation of the stress-activated cJun N-terminal kinase (JNK) pathway in lesional epidermis. Additionally, our data reveal a strong induction of STAT1 activation in lesional HS epidermis that likely results from IFNγ production and triggered expression of key inflammatory genes coordinating innate immune activation and the adaptive T cell response in HS.

CONCLUSIONS

Our data implicate a key role of stress signaling and JAK/STAT1 activation in disease progression of HS and suggest interference with JAK/STAT1 signaling as a potentially promising therapeutic approach for HS.

Salmonella Typhimurium and inflammation: a pathogen-centric affair

Microbial infections are controlled by host inflammatory responses that are initiated by innate immune receptors after recognition of conserved microbial products. As inflammation can also lead to disease, tissues that are exposed to microbial products such as the intestinal epithelium are subject to stringent regulatory mechanisms to prevent indiscriminate signalling through innate immune receptors. The enteric pathogen Salmonella enterica subsp. enterica serovar Typhimurium, which requires intestinal inflammation to sustain its replication in the intestinal tract, uses effector proteins of its type III secretion systems to trigger an inflammatory response without the engagement of innate immune receptors. Furthermore, S. Typhimurium uses a different set of effectors to restrict the inflammatory response to preserve host homeostasis. The S. Typhimurium-host interface is a remarkable example of the unique balance that emerges from the co-evolution of a pathogen and its host.

Novirhabdoviruses versus fish innate immunity: A review

Novirhabdoviruses belong to the Rhabdoviridae family of RNA viruses. All of the four members are pathogenic for bony fish. Particularly, Infectious hematopoietic necrosis virus (IHNV) and Viral hemorrhagic septicemia virus (VHSV) often cause mass animal deaths and huge economic losses, representing major obstacles to fish farming industry worldwide. The interactions between fish and novirhabdoviruses are becoming better understood. In this review, we will present our current knowledge of fish innate immunity, particularly type I interferon (IFN-I) response, against novirhabdoviral infection, and the evasion strategies exploited by novirhabdoviruses. Members of Toll-like receptors (TLRs) and RIG-I-like receptors (RLRs) appear to be involved in novirhabdovirus surveillance. NF-κB activation and IFN-I induction are primarily triggered for antiviral defense. Autophagy can also be induced by viral glycoprotein (G). Although sensitive to IFN-I, novirhabdoviruses have nucleoprotein (N), matrix protein (M), and non-virion protein (NV) to interfere with host signal transduction and gene expression steps toward antiviral state establishment. Moreover, novirhabdoviruses may exploit some microRNAs for immunosuppression.

Toll-interacting protein in the freshwater fish Labeo rohita exhibits conserved structural motifs of higher eukaryotes and is distinctly expressed in pathogen-associated molecular pattern stimulations and bacterial infections

Toll-interacting protein (Tollip) is a critical regulator of TOLL- like receptor (TLR)-signaling pathway. It is predominantly associated with TLR2 and TLR4 during acute inflammatory conditions and inhibits the TLR-mediated nuclear factor-kappa activation by suppressing the autophosphorylation of interleukin-1 receptor-associated kinase and its kinase activity. This article describes the Tollip of Labeo rohita (LrTollip), a highly valuable freshwater fish from the Indian subcontinent. The full-length LrTollip complementary DNA (1412 nucleotides) encodes a 276-amino acid (aa) protein, depicting a highly conserved target of the Myb1 (Tom1)-binding domain (TBD; 1-53 aa), conserved core domain 2 (C2; 54-151 aa), and coupling of ubiquitin to endoplasmic reticulum degradation (CUE; 231-273 aa) domains of mouse and human counterparts. The key amino acids exerting the critical functions of Tollip, such as phospholipids recognition and ubiquitination, are present in the C2 and CUE domains of LrTollip, respectively. LrTollip is widely expressed in the kidneys, gills, spleen, liver, and blood, and among these tested tissues, the highest expression is observed in blood. In response to TLR ligands and NOD-like receptor (NLR) ligands stimulations and Aeromonas hydrophila, Edwardsiella tarda, and Bacillus subtilis infections, LrTollip gene expression is induced in various organs/tissues with remarkable difference in their kinetics. These data together suggest the important role of LrTollip in TLR- and NLR-signal transduction pathways and immune-related diseases in fish.

The Salmonella effector protein SopD targets Rab8 to positively and negatively modulate the inflammatory response

The food-borne bacterial pathogen Salmonella Typhimurium uses a type III protein secretion system to deliver multiple proteins into host cells. These secreted effectors modulate the functions of host cells and activate specific signalling cascades that result in the production of pro-inflammatory cytokines and intestinal inflammation. Some of the Salmonella-encoded effectors counteract this inflammatory response and help to preserve host homeostasis. Here, we demonstrate that the Salmonella effector protein SopD, which is required for pathogenesis, functions to both activate and inhibit the inflammatory response by targeting the Rab8 GTPase, which is a negative regulator of inflammation. We show that SopD has GTPase-activating protein activity for Rab8 and, therefore, inhibits this GTPase and stimulates inflammation. We also show that SopD activates Rab8 by displacing it from its cognate guanosine dissociation inhibitor, resulting in the stimulation of a signalling cascade that suppresses inflammation. We solved the crystal structure of SopD in association with Rab8 to a resolution of 2.3 Å, which reveals a unique contact interface that underlies these complex interactions. These findings show the remarkable evolution of a bacterial effector protein to exert both agonistic and antagonistic activities towards the same host cellular target to modulate the inflammatory response.

Sox4 represses host innate immunity to facilitate pathogen infection by hijacking the TLR signaling networks

Toll-like receptors (TLRs) are essential for the protection of the host from pathogen infections by initiating the integration of contextual cues to regulate inflammation and immunity. However, without tightly controlled immune responses, the host will be subjected to detrimental outcomes. Therefore, it is important to balance the positive and negative regulations of TLRs to eliminate pathogen infection, yet avert harmful immunological consequences. This study revealed a distinct mechanism underlying the regulation of the TLR network. The expression of sex-determining region Y-box 4 (Sox4) is induced by virus infection in viral infected patients and cultured cells, which subsequently represses the TLR signaling network to facilitate viral replication at multiple levels by a distinct mechanism. Briefly, Sox4 inhibits the production of myeloid differentiation primary response gene 88 (MyD88) and most of the TLRs by binding to their promoters to attenuate gene transcription. In addition, Sox4 blocks the activities of the TLR/MyD88/IRAK4/TAK1 and TLR/TRIF/TRAF3/TBK1 pathways by repressing their key components. Moreover, Sox4 represses the activation of the nuclear factor kappa-B (NF-κB) through interacting with IKKα/α, and attenuates NF-kB and IFN regulatory factors 3/7 (IRF3/7) abundances by promoting protein degradation. All these contributed to the down-regulation of interferons (IFNs) and IFN-stimulated gene (ISG) expression, leading to facilitate the viral replications. Therefore, we reveal a distinct mechanism by which viral pathogens evade host innate immunity and discover a key regulator in host defense.

IFN-mediated negative feedback supports bacteria class-specific macrophage inflammatory responses

Despite existing evidence for tuning of innate immunity to different classes of bacteria, the molecular mechanisms used by macrophages to tailor inflammatory responses to specific pathogens remain incompletely defined. By stimulating mouse macrophages with a titration matrix of TLR ligand pairs, we identified distinct stimulus requirements for activating and inhibitory events that evoked diverse cytokine production dynamics. These regulatory events were linked to patterns of inflammatory responses that distinguished between Gram-positive and Gram-negative bacteria, both in vitro and after in vivo lung infection. Stimulation beyond a TLR4 threshold and Gram-negative bacteria-induced responses were characterized by a rapid type I IFN-dependent decline in inflammatory cytokine production, independent of IL-10, whereas inflammatory responses to Gram-positive species were more sustained due to the absence of this IFN-dependent regulation. Thus, disparate triggering of a cytokine negative feedback loop promotes tuning of macrophage responses in a bacteria class-specific manner and provides context-dependent regulation of inflammation dynamics.

Salmonella stimulates pro-inflammatory signalling through p21-activated kinases bypassing innate immune receptors

Microbial infections are most often countered by inflammatory responses that are initiated through the recognition of conserved microbial products by innate immune receptors and result in pathogen expulsion^1-6. However, inflammation can also lead to pathology. Tissues such as the intestinal epithelium, which are exposed to microbial products, are therefore subject to stringent negative regulatory mechanisms to prevent signalling through innate immune receptors^6-11. This presents a challenge to the enteric pathogen Salmonella Typhimurium, which requires intestinal inflammation to compete against the resident microbiota and to acquire the nutrients and electron acceptors that sustain its replication^12,13. We show here that S. Typhimurium stimulates pro-inflammatory signalling by a unique mechanism initiated by effector proteins that are delivered by its type III protein secretion system. These effectors activate Cdc42 and the p21-activated kinase 1 (PAK1) leading to the recruitment of TNF receptor-associated factor 6 (TRAF6) and mitogen-activated protein kinase kinase kinase 7 (TAK1), and the stimulation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) inflammatory signalling. The removal of Cdc42, PAK1, TRAF6 or TAK1 prevented S. Typhimurium from stimulating NF-κB signalling in cultured cells. In addition, oral administration of a highly specific PAK inhibitor blocked Salmonella-induced intestinal inflammation and bacterial replication in the mouse intestine, although it resulted in a significant increase in the bacterial loads in systemic tissues. Thus, S. Typhimurium stimulates inflammatory signalling in the intestinal tract by engaging critical downstream signalling components of innate immune receptors. These findings illustrate the unique balance that emerges from host-pathogen co-evolution, in that pathogen-initiated responses that help pathogen replication are also important to prevent pathogen spread to deeper tissues.

CgNrdp1, a conserved negative regulating factor of MyD88-dependent Toll like receptor signaling in oyster Crassostrea gigas

Toll like receptor (TLR) signaling cascades are under precise regulations to ensure the proper immune responses during various pathogen invasions. The neuregulin receptor degradation protein-1 (Nrdp1) has been demonstrated to be a novel negative regulator of TLR signaling by targeting MyD88 to induce degradation in mammals. In the present study, an Nrdp1 homologue, CgNrdp1, was identified from the genome of Pacific oyster Crassostrea gigas. It contained an open reading frame encoding a polypeptide of 315 amino acids which shared high identities with other homologues from different species. There was a conserved RING domain in CgNrdp1, indicating the functional E3 ubiquitin ligase activity. The bacterially expressed recombinant CgNrdp1 and CgMyD88 showed much stronger affinity compared to control groups in the ELISA assay, showing the interacting ability between CgNrdp1 and CgMyD88. When CgMyD88 or HsMyD88 was co-transfected with CgNrdp1 into HEK293T cells, the luciferase activities of NF-κB were significantly decreased compared to those in MyD88 single-transfection groups, indicating the conserved negative regulating function of CgNrdp1 on the MyD88 induced TLR signaling. These results indicated that CgNrdp1 was a negative regulator of TLR signaling in oyster and the Nrdp1-MyD88 axis was functional and highly conserved from mollusks to mammals in the negative regulation of TLR signaling.

The identification, characterization, and function of two TREMs genes in Chinese Yangzhou goose (Anas cygnoides)

Triggering receptor expressed on myeloid cells (TREM) is a cell-surface receptor primarily expressed on macrophages. Here, two novel TREM genes, AcTREM1 and AcTREM2, were identified from Anas cygnoides. AcTREM1 cDNA contained a putative signal peptide, two IG domains, and a transmembrane domain. The deduced AcTREM2 sequence also contained a signal peptide, an IG domain, and a transmembrane domain. qRT-PCR, fluorescence in situ hybridization, and immunofluorescence experiments showed that AcTREM1 and AcTREM2 were mainly expressed in the liver and spleen, and both genes and proteins were mainly distributed in cytoplasm. AcTREM1 expression in the liver and spleen was significantly upregulated following lipopolysaccharide (LPS) challenge at an early stage of infection and then decreased at a later stage. Changes in AcTREM2 expression were reciprocal to those of AcTREM1 in the liver and spleen after LPS challenge. Our results indicate that AcTREM1 and AcTREM2 participate in the antibacterial immunity of A. cygnoides.

Molecular Pathophysiology of Gout

Three contradictory clinical presentations of gout have puzzled clinicians and basic scientists for some time: first, the crescendo of sterile inflammation in acute gouty arthritis; second, its spontaneous resolution, despite monosodium urate (MSU) crystal persistence in the synovium; and third, immune anergy to MSU crystal masses observed in tophaceous or visceral gout. Here, we provide an update on the molecular pathophysiology of these gout manifestations, namely, how MSU crystals can trigger the auto-amplification loop of necroinflammation underlying the crescendo of acute gouty arthritis. We also discuss new findings, such as how aggregating neutrophil extracellular traps (NETs) might drive the resolution of arthritis and how these structures, together with granuloma formation, might support immune anergy, but yet promote tissue damage and remodeling during tophaceous gout.

The Role of Caveolin 1 in HIV Infection and Pathogenesis

Caveolin 1 (Cav-1) is a major component of the caveolae structure and is expressed in a variety of cell types including macrophages, which are susceptible to human immunodeficiency virus (HIV) infection. Caveolae structures are present in abundance in mechanically stressed cells such as endothelial cells and adipocytes. HIV infection induces dysfunction of these cells and promotes pathogenesis. Cav-1 and the caveolae structure are believed to be involved in multiple cellular processes that include signal transduction, lipid regulation, endocytosis, transcytosis, and mechanoprotection. Such a broad biological role of Cav-1/caveolae is bound to have functional cross relationships with several molecular pathways including HIV replication and viral-induced pathogenesis. The current review covers the relationship of Cav-1 and HIV in respect to viral replication, persistence, and the potential role in pathogenesis.

S100A8/A9 and S100A9 reduce acute lung injury

S100A8 and S100A9 are myeloid cell-derived proteins that are elevated in several types of inflammatory lung disorders. Pro- and anti-inflammatory properties are reported and these proteins are proposed to activate TLR4. S100A8 and S100A9 can function separately, likely through distinct receptors but a systematic comparison of their effects in vivo are limited. Here we assess inflammation in murine lung following S100A9 and S100A8/A9 inhalation. Unlike S100A8, S100A9 promoted mild neutrophil and lymphocyte influx, possibly mediated in part, by increased mast cell degranulation and selective upregulation of some chemokine genes, particularly CXCL-10. S100 proteins did not significantly induce proinflammatory mediators including TNF-α, interleukin-1β (IL-1β), IL-6 or serum amyloid A3 (SAA3). In contrast to S100A8, neither preparation induced S100A8 or IL-10 mRNA/protein in airway epithelial cells, or in tracheal epithelial cells in vitro. Like S100A8, S100A9 and S100A8/A9 reduced neutrophil influx in acute lung injury provoked by lipopolysaccharide (LPS) challenge but were somewhat less inhibitory, possibly because of differential effects on expression of some chemokines, IL-1β, SAA3 and IL-10. Novel common pathways including increased induction of an NAD⁺-dependent protein deacetylase sirtuin-1 that may reduce NF-κB signalling, and increased STAT3 activation may reduce LPS activation. Results suggest a role for these proteins in normal homeostasis and protective mechanisms in the lung.

Macrophage-epithelial interactions in pulmonary alveoli

Alveolar macrophages have been investigated for years by approaches involving macrophage extraction from the lung by bronchoalveolar lavage, or by cell removal from lung tissue. Since extracted macrophages are studied outside their natural milieu, there is little understanding of the extent to which alveolar macrophages interact with the epithelium, or with one another to generate the lung's innate immune response to pathogen challenge. Here, we review new evidence of macrophage-epithelial interactions in the lung, and we address the emerging understanding that the alveolar epithelium plays an important role in orchestrating the macrophage-driven immune response.

The Salmonella Effector Protein SopA Modulates Innate Immune Responses by Targeting TRIM E3 Ligase Family Members

Salmonella Typhimurium stimulates inflammatory responses in the intestinal epithelium, which are essential for its ability to replicate within the intestinal tract. Stimulation of these responses is strictly dependent on the activity of a type III secretion system encoded within its pathogenicity island 1, which through the delivery of effector proteins, triggers signaling pathways leading to inflammation. One of these effectors is SopA, a HECT-type E3 ligase, which is required for the efficient stimulation of inflammation in an animal model of Salmonella Typhimurium infection. We show here that SopA contributes to the stimulation of innate immune responses by targeting two host E3 ubiquitin ligases, TRIM56 and TRIM65. We also found that TRIM65 interacts with the innate immune receptor MDA5 enhancing its ability to stimulate interferon-β signaling. Therefore, by targeting TRIM56 and TRIM65, SopA can stimulate signaling through two innate immune receptors, RIG-I and MDA5. These findings describe a Salmonella mechanism to modulate inflammatory responses by directly targeting innate immune signaling mechanisms.

Salmonella Typhimurium, one of the main causes of food-borne illnesses, stimulates inflammatory responses in the intestinal epithelium. These responses are very important for the pathogen’s ability to secure nutrients within the intestinal tract. The ability of this pathogen to stimulate intestinal inflammation depends on a protein-delivery machine known as the type III secretion system. This system “injects” bacterial effector protein into host cells to modulate a variety of cellular functions for the pathogen’s benefit. We show here that one of these effector proteins, SopA, stimulates signaling pathways that can lead to inflammation. We report that SopA exerts its function by targeting two host E3 ubiquitin ligases, TRIM56 and TRIM65, which have the ability to enhance interferon-β expression through the innate immune receptors RIG-I and MDA5. These findings describe a Salmonella mechanism to stimulate inflammation by directly targeting innate immune signaling mechanisms.

Dual Activation of TRIF and MyD88 Adaptor Proteins by Angiotensin II Evokes Opposing Effects on Pressure, Cardiac Hypertrophy, and Inflammatory Gene Expression

Hypertension is recognized as an immune disorder whereby immune cells play a defining role in the genesis and progression of the disease. The innate immune system and its component toll-like receptors are key determinants of the immunologic outcome through their proinflammatory response. Toll-like receptor-activated signaling pathways use several adaptor proteins of which adaptor proteins myeloid differentiation protein 88 (MyD88) and toll-interleukin receptor domain-containing adaptor protein-inducing interferon-β (TRIF) define 2 major inflammatory pathways. In this study, we compared the contributions of MyD88 and TRIF adaptor proteins to angiotensin II (Ang II)-induced hypertension and cardiac hypertrophy in mice. Deletion of MyD88 did not prevent cardiac hypertrophy and the pressor response to Ang II tended to increase. Moreover, the increase in inflammatory gene expression (Tnfa, Nox4, and Agtr1a) was significantly greater in the heart and kidney of MyD88-deficient mice when compared with wild-type mice. Thus, pathways involving MyD88 may actually restrain the inflammatory responses. However, in mice with nonfunctional TRIF (Trif(mut) mice), Ang II-induced hypertension and cardiac hypertrophy were abrogated, and proinflammatory gene expression in heart and kidneys was unchanged or decreased. Our results indicate that Ang II induces activation of a proinflammatory innate immune response, causing hypertension and cardiac hypertrophy. These effects require functional adaptor protein TRIF-mediated pathways. However, the common MyD88-dependent signaling pathway, which is also activated simultaneously by Ang II, paradoxically exerts a negative regulatory influence on these responses.

Emerging role of SIGIRR rs7396562(T/G) polymorphism in systemic lupus erythematosus in a Chinese population

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease, with heterogeneous presentation. The aim of this study was to examine the association of a single-nucleotide polymorphism, rs7396562, of the interferon induced with single immunoglobulin IL-1-related receptor (SIGIRR) gene with SLE in a Chinese population. A total of 741 SLE patients and 731 healthy control subjects were enrolled in the present study. The genotyping of polymorphism (rs7396562) was determined by TaqMan allele discrimination assay on the 7,300 real-time polymerase chain reaction system. The frequency of T allele for rs7396562 in patients was significantly higher than in controls (T versus G, OR=1.318, 95 % confidence interval (CI)=1.139-1.525, P<0.001). Fortunately, some significant difference in genotype distribution was found between cases and controls (P<0.001). We also found some significant evidence for the association of the SIGIRR rs7396562 polymorphism with SLE between dominant and recessive model (TG+TT versus GG, P=0.002; TT versus TG+GG, P=0.002). We also analyzed the association of the SIGIRR rs7396562 T allele with clinical features; luckily, photosensitivity and malar rash had some significant signal with the SNP. In conclusion, our study represents the first report demonstrating an association of the SIGIRR rs7396562 polymorphism with SLE susceptibility in a Chinese population.

Alternatively spliced myeloid differentiation protein-2 inhibits TLR4-mediated lung inflammation

We previously identified a novel alternatively spliced isoform of human myeloid differentiation protein-2 (MD-2s) that competitively inhibits binding of MD-2 to TLR4 in vitro. In this study, we investigated the protective role of MD-2s in LPS-induced acute lung injury by delivering intratracheally an adenovirus construct that expressed MD-2s (Ad-MD-2s). After adenovirus-mediated gene transfer, MD-2s was strongly expressed in lung epithelial cells and readily detected in bronchoalveolar lavage fluid. Compared to adenovirus serotype 5 containing an empty vector lacking a transgene control mice, Ad-MD-2s delivery resulted in significantly less LPS-induced inflammation in the lungs, including less protein leakage, cell recruitment, and expression of proinflammatory cytokines and chemokines, such as IL-6, keratinocyte chemoattractant, and MIP-2. Bronchoalveolar lavage fluid from Ad-MD-2s mice transferred into lungs of naive mice before intratracheal LPS challenge diminished proinflammatory cytokine levels. As house dust mite (HDM) sensitization is dependent on TLR4 and HDM Der p 2, a structural homolog of MD-2, we also investigated the effect of MD-2s on HDM-induced allergic airway inflammation. Ad-MD-2s given before HDM sensitization significantly inhibited subsequent allergic airway inflammation after HDM challenge, including reductions in eosinophils, goblet cell hyperplasia, and IL-5 levels. Our study indicates that the alternatively spliced short isoform of human MD-2 could be a potential therapeutic candidate to treat human diseases induced or exacerbated by TLR4 signaling, such as Gram-negative bacterial endotoxin-induced lung injury and HDM-triggered allergic lung inflammation.

Regulation of toll-like receptor signaling by the SF3a mRNA splicing complex

The innate immune response plays a key role in fighting infection by activating inflammation and stimulating the adaptive immune response. However, chronic activation of innate immunity can contribute to the pathogenesis of many diseases with an inflammatory component. Thus, various negatively acting factors turn off innate immunity subsequent to its activation to ensure that inflammation is self-limiting and to prevent inflammatory disease. These negatively acting pathways include the production of inhibitory acting alternate proteins encoded by alternative mRNA splice forms of genes in Toll-like receptor (TLR) signaling pathways. We previously found that the SF3a mRNA splicing complex was required for a robust innate immune response; SF3a acts to promote inflammation in part by inhibiting the production of a negatively acting splice form of the TLR signaling adaptor MyD88. Here we inhibit SF3a1 using RNAi and subsequently perform an RNAseq study to identify the full complement of genes and splicing events regulated by SF3a in murine macrophages. Surprisingly, in macrophages, SF3a has significant preference for mRNA splicing events within innate immune signaling pathways compared with other biological pathways, thereby affecting the splicing of specific genes in the TLR signaling pathway to modulate the innate immune response.

Within minutes after we are exposed to pathogens, our bodies react with a rapid response known as the “innate immune response.” This arm of the immune response regulates the process of inflammation, in which various immune cells are recruited to sites of infection and are activated to produce a host of antimicrobial compounds. This response is critical to fight infection. However, this response, if it is activated too strongly or if it becomes chronic, can do damage and can contribute to numerous very common diseases ranging from atherosclerosis to asthma to cancer. Thus it is essential that this response be tightly regulated, turned on when we have an infection, and turned off when not needed. We are investigating a mechanism that helps turn off this response, to ensure that inflammation is limited to prevent inflammatory disease. This mechanism involves the production of alternate forms of RNAs and proteins that control inflammation. We have discovered that a protein known as SF3a1 can regulate the expression of these alternate inhibitory RNA forms and are investigating how to use this knowledge to better control inflammation.

The early induction of suppressor of cytokine signaling 1 and the downregulation of toll-like receptors 7 and 9 induce tolerance in costimulated macrophages

Toll-like receptors (TLR) 7 and 9 transduce a cellular signal through the MyD88-dependent pathway and induce the production of inflammatory mediators against microbial nucleotide components. The repeated stimulation of TLR4 leads to endotoxin tolerance, but the molecular mechanisms of tolerance induced through the costimulation of individual TLR has not yet been established, although endosomal TLRs share signaling pathways with TLR4. In the present study, mouse macrophages were simultaneously stimulated with the TLR7 agonist, gardiquimod (GDQ), and the TLR9 agonist, CpG ODN 1826, to examine the mechanism and effector functions of macrophage tolerance. Compared with individual stimulation, the costimulation of both TLRs reduced the secretion of TNF-α and IL-6 through the delayed activation of the NF-κB pathway; notably, IL-10 remained unchanged in costimulated macrophages. This tolerance reflected the early induction of suppressor of cytokine signaling-1 (SOCS-1), according to the detection of elevated TNF-α secretion and restored NF-κB signaling in response to the siRNA-mediated abrogation of SOCS-1 signaling. In addition, the restimulation of each TLRs using the same ligand significantly reduced the expression of both TLRs in endosomes. These findings revealed that the costimulation of TLR7 and TLR9 induced macrophage tolerance via SOCS-1, and the restimulation of each receptor or both TLR7 and TLR9 downregulated TLR expression through a negative feedback mechanisms that protects the host from excessive inflammatory responses. Moreover, the insufficient and impaired immune response in chronic viral infection might also reflect the repeated and simultaneous stimulation of those endosomal TLRs.

The Subtleties and Contrasts of the LeuO Regulator in Salmonella Typhi: Implications in the Immune Response

Salmonella are facultative intracellular pathogens. Salmonella infection occurs mainly by expression of two Salmonella pathogenicity Islands (SPI-1 and SPI-2). SPI-1 encodes transcriptional factors that participate in the expression of virulence factors encoded in the island. However, there are transcriptional factors encoded outside the island that also participate in the expression of SPI-1-encoded genes. Upon infection, bacteria are capable of avoiding the host immune response with several strategies that involve several virulence factors under the control of transcriptional regulators. Interestingly, LeuO a transcriptional global regulator which is encoded outside of any SPI, is proposed to be part of a complex regulatory network that involves expression of several genes that help bacteria to survive stress conditions and, also, induces the expression of porins that have been shown to be immunogens and can thus be considered as antigenic candidates for acellular vaccines. Hence, the understanding of the LeuO regulon implies a role of bacterial genetic regulation in determining the host immune response.

Extracellular signal-regulated kinase mediates expression of arginase II but not inducible nitric-oxide synthase in lipopolysaccharide-stimulated macrophages

The mitogen-activated protein kinases (MAPK) have been shown to participate in iNOS induction following lipopolysaccharide (LPS) stimulation, while the role of MAPKs in the regulation of arginase remains unclear. We hypothesized that different MAPK family members are involved in iNOS and arginase expression following LPS stimulation. LPS-stimulated RAW 264.7 cells exhibited increased protein and mRNA levels for iNOS, arginase I, and arginase II; although the induction of arginase II was more robust than that for arginase I. A p38 inhibitor completely prevented iNOS expression while it only attenuated arginase II induction. In contrast, a MEK1/2 inhibitor (ERK pathway) completely abolished arginase II expression while actually enhancing iNOS induction in LPS-stimulated cells. Arginase II promoter activity was increased by ∼4-fold following LPS-stimulation, which was prevented by the ERK pathway inhibitor. Arginase II promoter activity was unaffected by a p38 inhibitor or JNK pathway interference. Transfection with a construct expressing a constitutively active RAS mutant increased LPS-induced arginase II promoter activity, while transfection with a vector expressing a dominant negative ERK2 mutant or a vector expressing MKP-3 inhibited the arginase II promoter activity. LPS-stimulated nitric oxide (NO) production was increased following siRNA-mediated knockdown of arginase II and decreased when arginase II was overexpressed. Our results demonstrate that while both the ERK and p38 pathways regulate arginase II induction in LPS-stimulated macrophages, iNOS induction by LPS is dependent on p38 activation. These results suggest that differential inhibition of the MAPK pathway may be a potential therapeutic strategy to regulate macrophage phenotype.

Regulation of mIκBNS stability through PEST-mediated degradation by proteasome

Negative regulatory proteins in a cytokine signaling play a critical role in restricting unwanted excess activation of the signaling pathway. At the same time, negative regulatory proteins need to be removed rapidly from cells to respond properly to the next incoming signal. A nuclear IκB protein called IκBNS is known to inhibit a subset of NF-κB target genes upon its expression by NF-κB activation. Here, we show a mechanism to control the stability of mIκBNS which might be important for cells to prepare the next round signaling. We found that mIκBNS is a short-lived protein of which the stability is controlled by proteasome, independent of ubiquitylation process. We identified that the N-terminal PEST sequence in mIκBNS was critical for the regulation of stability.

Limiting of the innate immune response by SF3A-dependent control of MyD88 alternative mRNA splicing

Controlling infectious disease without inducing unwanted inflammatory disease requires proper regulation of the innate immune response. Thus, innate immunity needs to be activated when needed during an infection, but must be limited to prevent damage. To accomplish this, negative regulators of innate immunity limit the response. Here we investigate one such negative regulator encoded by an alternative splice form of MyD88. MyD88 mRNA exists in two alternative splice forms: MyD88L, a long form that encodes a protein that activates innate immunity by transducing Toll-like receptor (TLR) signals; and a short form that encodes a different protein, MyD88S, that inhibits the response. We find that MyD88S levels regulate the extent of inflammatory cytokine production in murine macrophages. MyD88S mRNA levels are regulated by the SF3A and SF3B mRNA splicing complexes, and these mRNA splicing complexes function with TLR signaling to regulate MyD88S production. Thus, the SF3A mRNA splicing complex controls production of a negative regulator of TLR signaling that limits the extent of innate immune activation.

Salmonella modulation of host cell gene expression promotes its intracellular growth

Salmonella Typhimurium has evolved a complex functional interface with its host cell largely determined by two type III secretion systems (T3SS), which through the delivery of bacterial effector proteins modulate a variety of cellular processes. We show here that Salmonella Typhimurium infection of epithelial cells results in a profound transcriptional reprogramming that changes over time. This response is triggered by Salmonella T3SS effector proteins, which stimulate unique signal transduction pathways leading to STAT3 activation. We found that the Salmonella-stimulated changes in host cell gene expression are required for the formation of its specialized vesicular compartment that is permissive for its intracellular replication. This study uncovers a cell-autonomous process required for Salmonella pathogenesis potentially opening up new avenues for the development of anti-infective strategies that target relevant host pathways.

Essential for the ability of Salmonella Typhimurium to cause disease is the function of a type III secretion system (T3SS) encoded within its pathogenicity island 1 (SPI-1), which through the delivery of bacterial effector proteins modulates a variety of cellular functions. This study reports that the infection of mammalian cells with Salmonella Typhimurium results in a profound reprogramming of gene expression that changes over time. The stimulation of this response requires the activity of a specific subset of bacterial T3SS effector proteins, which stimulate unique signal transduction pathways leading to STAT3 activation. We found that the Salmonella-stimulated changes in host cell gene expression are required for its intracellular replication. Targeting the mechanisms described in this study may lead to the development of novel anti-infective strategies.

Genome-wide transcriptional analysis of differentially expressed genes in flagellin-pretreated mouse corneal epithelial cells in response to Pseudomonas aeruginosa: involvement of S100A8/A9

We previously showed that pre-exposure of the cornea to Toll-like receptor 5 ligand flagellin induces profound mucosal innate protection against infections by modifying gene expression. Taking advantage of easily procurable epithelial cell population, this study is the first report to use genome-wide cDNA microarray approach to document genes associated with flagellin-induced protection against Pseudomonas aeruginosa in corneal epithelial cells (CECs). Infection altered the expression of 675 genes (497 up and 178 down), while flagellin pretreatment followed by infection resulted in a great increase in 890 gene upregulated and 37 genes downregulated. Comparing these two groups showed 209 differentially expressed genes (157 up, 52 down). Notably, among 114 genes categorized as defense related, S100A8/A9 are the two most highly induced genes by flagellin, and their expression in the corneal was confirmed by realtime PCR and immunohistochemistry. Neutralization of S100A8 and, to a less extent, A9, resulted in significantly increased bacterial burden and severe keratitis. Collectively, our study identifies many differentially expressed genes by flagellin in CECs in response to Pseudomonas. These novel gene expression signatures provide new insights and clues into the nature of protective mechanisms established by flagellin and new therapeutic targets for reducing inflammation and for controlling microbial infection.

Osteoclasts and CD8 T cells form a negative feedback loop that contributes to homeostasis of both the skeletal and immune systems

There are a number of dynamic regulatory loops that maintain homeostasis of the immune and skeletal systems. In this review, we highlight a number of these regulatory interactions that contribute to maintaining homeostasis. In addition, we review data on a negative regulatory feedback loop between osteoclasts and CD8 T cells that contributes to homeostasis of both the skeletal and immune systems.

A critical role for MAPK signalling pathways in the transcriptional regulation of toll like receptors

Toll-like Receptors (TLR) are phylogenetically conserved transmembrane proteins responsible for detection of pathogens and activation of immune responses in diverse animal species. The stimulation of TLR by pathogen-derived molecules leads to the production of pro-inflammatory mediators including cytokines and nitric oxide. Although TLR-induced events are critical for immune induction, uncontrolled inflammation can be life threatening and regulation is a critical feature of TLR biology. We used an avian macrophage cell line (HD11) to determine the relationship between TLR agonist-induced activation of inflammatory responses and the transcriptional regulation of TLR. Exposure of macrophages to specific TLR agonists induced upregulation of cytokine and nitric oxide pathways that were inhibited by blocking various components of the TLR signalling pathways. TLR activation also led to changes in the levels of mRNA encoding the TLR responsible for recognising the inducing agonist (cognate regulation) and cross-regulation of other TLR (non-cognate regulation). Interestingly, in most cases, regulation of TLR mRNA was independent of NFκB activity but dependent on one or more of the MAPK pathway components. Moreover, the relative importance of ERK, JNK and p38 was dependent upon both the stimulating agonist and the target TLR. These results provide a framework for understanding the complex pathways involved in transcriptional regulation of TLR, immune induction and inflammation. Manipulation of these pathways during vaccination or management of acute inflammatory disease may lead to improved clinical outcome or enhanced vaccine efficacy.

TLR-4-dependent and -independent mechanisms of fetal brain injury in the setting of preterm birth

In this study, we sought to assess how essential activation of toll-like receptor 4 (TLR-4) is to fetal brain injury from intrauterine inflammation. Both wild-type and TLR-4 mutant fetal central nervous system cells were exposed to inflammation using lipopolysaccharide in vivo or in vitro. Inflammation could not induce neuronal injury in the absence of glial cells, in either wild-type or TLR-4 mutant neurons. However, injured neurons could induce injury in other neurons regardless of TLR-4 competency. Our results indicate that initiation of neuronal injury is a TLR-4-dependent event, while propagation is a TLR-4-independent event.

Extracellular nucleotide inhibits cell proliferation and negatively regulates Toll-like receptor 4 signalling in human progenitor endothelial cells

Extracellular nucleotides mediate a wide range of physiological effects by interacting with plasma membrane P2 purinergic receptors. P2 receptors are expressed in certain kinds of stem cells, and function to induce cytokine expression and to modulate cell proliferation. We have analysed the expression and the function of P2 receptors in human umbilical cord blood-derived EPCs (endothelial progenitor cells). EPCs expressed P2X4,6,7 and P2Y2,4,11,13,14 receptors and extracellular ATP inhibited EPCs proliferation. As in a previous study, EPCs expressed functional TLR4 (Toll-like receptor 4) and activation of TLR4 by LPS (lipopolysaccharide) evoked a pro-inflammatory immune response. When human EPCs were stimulated with LPS and nucleotides, ATP or UTP inhibited the expression of pro-inflammatory cytokines including MCP-1 (monocyte chemoattractant protein-1), IFNα (interferon α), TNFα (tumour necrosis factor α) and adhesion molecule VCAM-1 (vascular cell adhesion molecule 1) induced by LPS. ATP and UTP also down-regulated the gene expression of TLR4, CD14 and MyD88 (myeloid differentiation factor 88), a TLR adaptor molecule, and protein expression of CD14 and MyD88. Moreover, the phosphorylation of NF-κB (nuclear factor κB) p65 induced by TLR4 activation was inhibited partly by ATP or UTP at concentrations of 1-5 μM. These results suggest that extracellular nucleotides negatively regulate EPCs proliferation and TLR4 signalling.

Caveolin-1-mediated negative signaling plays a critical role in the induction of regulatory dendritic cells by DNA and protein coimmunization

Induction of Ag-specific regulatory T cells (iTregs) by vaccination is a promising strategy for treating autoimmune diseases. We previously demonstrated that DNA and protein covaccination converted naive T cells to Ag-specific iTregs by inducing CD11c+CD40(low)IL-10+ regulatory dendritic cells (DCregs). However, it is unclear how coimmunization induces the DCregs. In this paper, we report that the event is initiated by coentry of sequence-matched DNA and protein immunogens into the same DC via caveolae-mediated endocytosis, which leads to inhibition of phosphorylation of caveolin-1 (Cav-1), the main component of caveolae, and upregulation of Tollip. This triggers downstream signaling that upregulates suppressor of cytokine signaling 1 and downregulates NF-κB and STAT-1α. Silencing either Cav-1 or Tollip blocks the negative signaling, leading to upregulated expression of CD40, downregulated production of IL-10, and loss of iTreg-inducing function. We further show that DCregs can be induced in culture from primary DCs and JAWS II DC lines by feeding them sequence-matched DNA and protein immunogens. The in vitro-generated DCregs are effective in ameliorating autoimmune and inflammatory diseases in several mouse models. Our study thus suggests that DNA and protein coimmunization induces DCregs through Cav-1- and Tollip-mediated negative signaling. It also describes a novel method for generating therapeutic DCregs in vitro.

Toll-like receptor 2 knockout mice showed increased periapical lesion size and osteoclast number

INTRODUCTION

The aim of this study was to characterize the formation and progression of experimentally induced periapical lesions in TLR2 knockout (TLR2 KO) mice.

METHODS

Periapical lesions were induced in molars of 28 wild type (WT) and 27 TLR2 KO mice. After 7, 21, and 42 days, the animals were euthanized, and the mandibles were subjected to histotechnical processing. Hematoxylin-eosin-stained sections were examined under conventional light microscopy for the description of pulpal, apical, and periapical features and under fluorescence microscopy for the determination of the periapical lesion size. The subsequent sections were evaluated by tartrate resistant acid phosphatase histoenzymology (osteoclasts), Brown and Brenn staining (bacteria), and immunohistochemistry (RANK, RANKL, and OPG). Data were analyzed by the Mann-Whitney U and Kruskal-Wallis tests (α = 0.05).

RESULTS

The WT group showed significant differences (P < .05) in the periapical lesion size and the osteoclast number between 7 and 42 days and between 21 and 42 days. In the TLR2 KO group, significant differences (P < .05) in the periapical lesion size and the osteoclast number were found between 7 days and the other periods. There was a significant difference (P < .05) between the 2 types of animal regarding the periapical lesion size, which was larger in the TLR2 KO animals. No significant differences (P > .05) were found between WT and TLR2 KO mice related to the pulpal, apical, and periapical features; bacteria localization; and immunohistochemical results (except for RANK expression).

CONCLUSIONS

TLR2 KO animals developed larger periapical lesions with a greater number of osteoclasts, indicating the important role of this receptor in the host's immune and inflammatory response to root canal and periradicular infection.

Dual or triple activation of TLR7, TLR8, and/or TLR9 by single-stranded oligoribonucleotides

The toll-like receptors (TLRs) 7, 8, and 9 stimulate innate immune responses upon recognizing pathogen nucleic acids. Certain GU- or AU-rich RNA sequences were described to differentiate between human TLR7- and TLR8-mediated immune effects. Those single-stranded RNA molecules require endosomal delivery for stabilization against ribonucleases. We have discovered RNA sequences that preferentially activate TLR7, form higher ordered structures, and do not require specific cellular delivery. In addition, a dual activation of TLR8 and TLR9 without affecting TLR7 can be achieved by chimeric molecules consisting of GU-rich RNA and Cytosin (C) phosphordiester or phosphorthioat (p) guanine (CpG) motif DNA sequences. Such chimeras stimulate TLR9-mediated type I interferon (IFN) and TLR8-depending proinflammatory cytokine and chemokine production upon primary human cell activation. However, an RNA-dependent TLR7 IFN-α cytokine release is suppressed by the phosphorothioate DNA sequence contained in the chimeric molecule. To convert the immune response of a single-stranded RNA from TLR7/8 to TLR9, a simple chemical modification at the 5' end proves to be sufficient. Such 8-oxo-2'-deoxy-guanosine or 8-bromo-2'-deoxy-guanosine modifications of the first guanosine in GU-rich single-stranded RNAs convert the immune response to include TLR9 activation and demonstrate strong additive effects for type I IFN immune responses in human primary cells.

Daily exposure to dust alters innate immunity

Pig farmers are exposed to organic material in pig barns on a daily basis and have signs of an ongoing chronic airway inflammation and increased prevalence of chronic inflammatory airway diseases, predominantly chronic bronchitis. Interestingly, the inflammatory response to acute exposure to organic dust is attenuated in farmers. The aim of the study was to closer characterize innate immunity features in blood and airways in farmers and in naïve, non-exposed, controls. The expression of pattern recognition receptors (TLR2, TLR4 and CD14) whose ligands are abundant in pig barn dust and adhesion proteins (CD11b, CD62L and CD162L) on blood and sputum neutrophils in pig farmers and soluble TLR2 and CD14 (sTLR2 and sCD14) in blood and sputum were assessed in pig farmers and previously unexposed controls. The release of pro-inflammatory cytokines from blood cells stimulated with LPS ex vivo was measured in the absence and presence of anti-ST2. We also examined, in a separate study population, serum levels of soluble ST2 (sST2), before and after exposure in a pig barn and a bronchial LPS challenge. Farmers had signs of ongoing chronic inflammation with increased number of blood monocytes, and decreased expression of CD62L and CD162 on blood neutrophils. Farmers also had lower levels of sTLR2 and sCD14 in sputum and reduced expression of CD14 on sputum neutrophils than controls. Exposure to organic dust and LPS induced increase of serum sST2 in controls but not in farmers. In conclusion, farmers have signs of local and systemic inflammation associated with altered innate immunity characteristics.

Common polymorphisms in the PKP3-SIGIRR-TMEM16J gene region are associated with susceptibility to tuberculosis

BACKGROUND

Tuberculosis has been associated with genetic variation in host immunity. We hypothesized that single-nucleotide polymorphisms (SNPs) in SIGIRR, a negative regulator of Toll-like receptor/IL-1R signaling, are associated with susceptibility to tuberculosis.

METHODS

We used a case-population study design in Vietnam with cases that had either tuberculous meningitis or pulmonary tuberculosis. We genotyped 6 SNPs in the SIGIRR gene region (including the adjacent genes PKP3 and TMEM16J) in a discovery cohort of 352 patients with tuberculosis and 382 controls. Significant associations were genotyped in a validation cohort (339 patients with tuberculosis, 376 controls).

RESULTS

Three SNPs (rs10902158, rs7105848, rs7111432) were associated with tuberculosis in discovery and validation cohorts. The polymorphisms were associated with both tuberculous meningitis and pulmonary tuberculosis and were strongest with a recessive genetic model (odds ratios, 1.5-1.6; P = .0006-.001). Coinheritance of these polymorphisms with previously identified risk alleles in Toll-like receptor 2 and TIRAP was associated with an additive risk of tuberculosis susceptibility.

CONCLUSIONS

These results demonstrate a strong association of SNPs in the PKP3-SIGIRR-TMEM16J gene region and tuberculosis in discovery and validation cohorts. To our knowledge, these are the first associations of polymorphisms in this region with any disease.

Toll-like receptor--a potent driving force behind rheumatoid arthritis

Toll like receptor (TLR), one of the key functions of innate immune system, can recognize not only exogenous pathogen-associated molecular patterns, namely PAMPs, but also endogenous molecules created upon tissue injury, sterile inflammation and degeneration. Endogenous TLR ligands are called as damage-associated molecular patters (DAMPs), including endogenous molecules released by activated and necrotic cells, and extracellular matrix molecules. DAMPs are also known as alarmins. TLR research has brought about new insights in the rheumatic diseases. Previous reports suggest that TLRs and the signal pathways intensively contribute to the pathogenesis of rheumatoid arthritis (RA) and other arthritic conditions with interaction of various TLR ligands. Accumulated knowledge of TLR system is summarized to overlook TLRs and the signaling pathway in arthritis conditions, with special reference to RA.

Pre-treatment of recombinant mouse MFG-E8 downregulates LPS-induced TNF-α production in macrophages via STAT3-mediated SOCS3 activation

Milk fat globule-epidermal growth factor factor 8 (MFG-E8) regulates innate immune function by modulating cellular signaling, which is less understood. Herein, we aimed to investigate the direct anti-inflammatory role of MFG-E8 in macrophages by pre-treatment with recombinant murine MFG-E8 (rmMFG-E8) followed by stimulation with LPS in RAW264.7 cells and in peritoneal macrophages, isolated from wild-type (WT) or MFG-E8^−/− mice. RAW264.7 cells and mouse peritoneal macrophages treated with rmMFG-E8 significantly downregulated LPS-induced TNF-α mRNA by 25% and 24%, and protein levels by 29% and 23%, respectively (P<0.05). Conversely, peritoneal macrophages isolated from MFG-E8^−/− mice produced 28% higher levels of TNF-α, as compared to WT mice when treated with LPS. In in vivo, endotoxemia induced by intraperitoneal injection of LPS (5 mg/kg BW), at 4 h after induction, serum level of TNF-α was significantly higher in MFG-E8^−/− mice (837 pg/mL) than that of WT (570 pg/mL, P<0.05). To elucidate the direct anti-inflammatory effect of MFG-E8, we examined STAT3 and its target gene, SOCS3. Treatment with rmMGF-E8 significantly induced pSTAT3 and SOCS3 in macrophages. Similar results were observed in in vivo treatment of rmMFG-E8 in peritoneal cells and splenic tissues. Pre-treatment with rmMFG-E8 significantly reduced LPS-induced NF-κB p65 contents. These data clearly indicated that rmMFG-E8 upregulated SOCS3 which in turn interacted with NF-κB p65, facilitating negative regulation of TLR4 signaling for LPS-induced TNF-α production. Our findings strongly suggest that MFG-E8 is a direct anti-inflammatory molecule, and that it could be developed as a therapy in attenuating inflammation and tissue injury.

Intracellular nucleic acid sensors and autoimmunity

A collection of molecular sensors has been defined by studies in the last decade that can recognize a diverse array of pathogens and initiate protective immune and inflammatory responses. However, if the molecular signatures recognized are shared by both foreign and self-molecules, as is the case of nucleic acids, then the responses initiated by these sensors may have deleterious consequences. Notably, this adverse occurrence may be of primary importance in autoimmune disease pathogenesis. In this case, microbe-induced damage or mishandled physiologic processes could lead to the generation of microparticles containing self-nucleic acids. These particles may inappropriately gain access to the cytosol or endolysosomes and, hence, engage resident RNA and DNA sensors. Evidence, as reviewed here, strongly indicates that these sensors are primary contributors to autoimmune disease pathogenesis, spearheading efforts toward development of novel therapeutics for these disorders.

Recurrent aphthous ulcers--a Toll-like receptor-mediated disease?

BACKGROUND

Recurrent aphthous ulcer (RAU) is characterized by acute and painful inflammatory ulcerations, which heal spontaneously but tend to recur. Many pathogens have been proposed as causative agents, but none has been consistently proven. According to our hypothesis, RAU is an autoinflammatory disorder triggered by pathogen-associated molecular patterns (PAMPs) shared by different pathogenic and commensal microbes.

METHODS

PAMP-reactive Toll-like receptors (TLRs) were mapped in oral epithelium in healthy controls compared to RAU.

RESULTS

In controls, the superficial epithelium formed a TLR(-), a PAMP non-reactive physical barrier zone, but all TLRs were found deeper in the epithelium, usually restricted to suprabasal and basal cell layers. In RAU, the epithelial TLR polarity was lost: TLRs 1, 2, 5, 7, and 8 were found throughout the epithelium, but also TLRs 4, 6, and 10 extended higher up than normally, whereas TLR-3 was almost lost in RAU. In RAU lesions, connective tissue stroma was heavily infiltrated by TLR(+) inflammatory cells.

CONCLUSIONS

Normal TLR architecture prevents inflammatory responses against normal microbes but still contains a deep TLR(+) , PAMP-reactive dormant defense zone. In RAU, the TLR(+), PAMP-reactive zone extends to surface or subsurface exposed to microbial PAMPs. TLR reactivity is further enhanced by recruitment of inflammatory leukocytes forming a new deep line of defense. The organization of the TLR system in healthy mucosa and its changes in RAU are compatible with active pathogenic involvement of TLRs, which together with the typical clinical picture and course suggest that RAU is a TLR-mediated disease.