Interleukin 1 receptor-associated kinase m impairs host defense during pneumococcal pneumonia

The IRAK-M death domain: a tale of three surfaces

The anti-inflammatory interleukin-1 receptor associated kinase-M (IRAK-M) is a negative regulator of MyD88/IRAK-4/IRAK-1 signaling. However, IRAK-M has also been reported to activate NF-κB through the MyD88/IRAK-4/IRAK-M myddosome in a MEKK-3 dependent manner. Here we provide support that IRAK-M uses three surfaces of its Death Domain (DD) to activate NF-κB downstream of MyD88/IRAK-4/IRAK-M. Surface 1, with central residue Trp74, binds to MyD88/IRAK-4. Surface 2, with central Lys60, associates with other IRAK-M DDs to form an IRAK-M homotetramer under the MyD88/IRAK-4 scaffold. Surface 3; with central residue Arg97 is located on the opposite side of Trp74 in the IRAK-M DD tetramer, lacks any interaction points with the MyD88/IRAK-4 complex. Although the IRAK-M DD residue Arg97 is not directly involved in the association with MyD88/IRAK-4, Arg97 was responsible for 50% of the NF-κB activation though the MyD88/IRAK-4/IRAK-M myddosome. Arg97 was also found to be pivotal for IRAK-M's interaction with IRAK-1, and important for IRAK-M's interaction with TRAF6. Residue Arg97 was responsible for 50% of the NF-κB generated by MyD88/IRAK-4/IRAK-M myddosome in IRAK-1/MEKK3 double knockout cells. By structural modeling we found that the IRAK-M tetramer surface around Arg97 has excellent properties that allow formation of an IRAK-M homo-octamer. This model explains why mutation of Arg97 results in an IRAK-M molecule with increased inhibitory properties: it still binds to myddosome, competing with myddosome IRAK-1 binding, while resulting in less NF-κB formation. The findings further identify the structure-function properties of IRAK-M, which is a potential therapeutic target in inflammatory disease.

Exosomes derived miR-362 exacerbates pneumonia by increasing Interleukin-6 via targeting VENTX

Pneumonia is a condition characterized by lung damage resulting from a robust immune response by the host. While the defense and immunity against bacterial lung infections have been extensively studied, little is known about the specific immune factors involved in the progression of bacterial pneumonia. To address this knowledge gap, our study aimed to compare normal lung tissues with pneumonia tissues using various techniques, including HE staining, RNA sequencing, RT-PCR, and Elisa assay. Our analysis revealed a significant increase in the levels of interleukin-6 (IL-6) in pneumonia tissues compared to normal lung tissues. To further investigate the underlying mechanism, we extracted exosomes from both pneumonia and normal lung tissues using ultracentrifugation. The exosomes were then examined using electron microscopy, diameter analysis, and western blot assay. RNA sequencing of the exosomes revealed an upregulation of several microRNAs (miRNAs), with miR-362 exhibiting the most significant change. This finding was confirmed through RT-PCR analysis conducted on lung tissues and alveolar lavage fluid. To gain insights into the specific target genes of miR-362, we employed bioinformatics analysis, which identified VENTX as a potential target gene. This finding was further validated through RT-PCR, western blot, and luciferase assay. Our experimental evidence demonstrated that miR-362 regulates VENTX expression, as evidenced by the use of miR-362 mimics or inhibitors on lung cells. Furthermore, we discovered that exosomes derived from pneumonia tissues upregulate IL-6 production through the miR-362/VENTX axis. Importantly, the blocking of IL-6 generation, which is facilitated by miR-362 inhibitor and VENTX overexpression lentivirus, can be achieved by treating exosomes. Moreover, we conducted in vivo experiments using pneumonia models. Rats were treated with IL-6, miR-362 mimics, or VENTX knock-down lentivirus. The results demonstrated a worse prognosis for rats treated with these factors, indicating their potential as prognostic markers. Taken together, our study suggests that exosomes facilitate IL-6 generation by transferring miR-362, thereby suppressing VENTX transcription. Consequently, the IL-6/miR-362/VENTX axis emerges as a promising therapeutic target for pneumonia.

Gut Microbiota Protected Against pseudomonas aeruginosa Pneumonia via Restoring Treg/Th17 Balance and Metabolism

Backgrounds and Purpose

The theory of “entero-pulmonary axis” proves that pneumonia leads to gut microbiota disturbance and Treg/Th17 immune imbalance. This study is aimed to explore the potential mechanism of fecal microbiota transplantation (FMT) in the treatment of Pseudomonas aeruginosa pneumonia, in order to provide new insights into the treatment of pneumonia.

Methods

Pseudomonas aeruginosa and C57/BL6 mice were used to construct the acute pneumonia mouse model, and FMT was treated. Histopathological changes in lung and spleen were observed by HE staining. The expression of CD25, Foxp3 and IL-17 was observed by immunofluorescence. The proportion of Treg and Th17 cells was analyzed by flow cytometry. Serum IL-6, LPS, and IFN-γ levels were detected by ELISA. The expression of TNF-α, IFN-γ, IL-6, IL-2, Foxp3, IL-17, IL-10, and TGFβ1 in lung tissue homogenate was detected by qRT-PCR. 16S rRNA sequencing and non-targeted metabolomics were used to analyze gut microbiota and metabolism.

Results

Pseudomonas aeruginosa caused the decrease of body weight, food and water intake, lung tissue, and spleen injury in mice with pneumonia. Meanwhile, it caused lung tissue and serum inflammation, and Treg/Th17 cell imbalance in mice with pneumonia. Pseudomonas aeruginosa reduced the diversity and number of gut microbiota in pneumonia mice, resulting in metabolic disorders, superpathway of quinolone and alkylquinolone biosynthesis. It also led to the decrease of 2-heptyl-3-hydroxy-4(1H)-quinolone biosynthesis, and the enrichment of Amino sugar and nucleotide sugar metabolism. FMT with or without antibiotic intervention restored gut microbiota abundance and diversity, suppressed inflammation and tissue damage, and promoted an immunological balance of Treg/Th17 cells in mice with pneumonia. In addition, FMT inhibited the aerobactin biosynthesis, 4-hydroxyphenylacetate degradation, superpathway of lipopolysaccharide biosynthesis and L-arabinose degradation IV function of microbiota, and improved amino sugar and nucleotide sugar metabolism.

Conclusions

FMT restored the Treg/Th17 cells’ balance and improved inflammation and lung injury in mice with Pseudomonas aeruginosa pneumonia by regulating gut microbiota disturbance and metabolic disorder.

A systematic review and meta-analyses of interleukin-1 receptor associated kinase 3 (IRAK3) action on inflammation in in vivo models for the study of sepsis

Background

Interleukin-1 receptor associated kinase 3 (IRAK3) is a critical modulator of inflammation and is associated with endotoxin tolerance and sepsis. Although IRAK3 is known as a negative regulator of inflammation, several studies have reported opposing functions, and the temporal actions of IRAK3 on inflammation remain unclear. A systematic review and meta-analyses were performed to investigate IRAK3 expression and its effects on inflammatory markers (TNF-α and IL-6) after one- or two-challenge interventions, which mimic the hyperinflammatory and immunosuppression phases of sepsis, respectively, using human or animal in vivo models.

Methods

This systematic review and meta-analyses has been registered in the Open Science Framework (OSF) (Registration DOI: 10.17605/OSF.IO/V39UR). A systematic search was performed to identify in vivo studies reporting outcome measures of expression of IRAK3 and inflammatory markers. Meta-analyses were performed where sufficient data was available.

Results

The search identified 7778 studies for screening. After screening titles, abstracts and full texts, a total of 49 studies were included in the systematic review. The review identified significant increase of IRAK3 mRNA and protein expression at different times in humans compared to rodents following one-challenge, whereas the increases of IL-6 and TNF-α protein expression in humans were similar to rodent in vivo models. Meta-analyses confirmed the inhibitory effect of IRAK3 on TNF-α mRNA and protein expression after two challenges.

Conclusions

A negative correlation between IRAK3 and TNF-α expression in rodents following two challenges demonstrates the association of IRAK3 in the immunosuppression phase of sepsis. Species differences in underlying biology affect the translatability of immune responses of animal models to human, as shown by the dissimilarity in patterns of IRAK3 mRNA and protein expression between humans and rodents following one challenge that are further influenced by variations in experimental procedures.

Analysis of interleukin-1 receptor associated kinase-3 (IRAK3) function in modulating expression of inflammatory markers in cell culture models: A systematic review and meta-analysis

BACKGROUND

IRAK3 is a critical modulator of inflammation in innate immunity. IRAK3 is associated with many inflammatory diseases, including sepsis, and is required in endotoxin tolerance to maintain homeostasis of inflammation. The impact of IRAK3 on inflammatory markers such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in cell culture models remains controversial.

OBJECTIVE

To analyse temporal effects of IRAK3 on inflammatory markers after one- or two-challenge interventions in cell culture models.

METHODS

A systematic search was performed to identify in vitro cell studies reporting outcome measures of expression of IRAK3 and inflammatory markers. Meta-analyses were performed where sufficient data were available. Comparisons of outcome measures were performed between different cell lines and human and mouse primary cells.

RESULTS

The literature search identified 7766 studies for screening. After screening titles, abstracts and full-texts, a total of 89 studies were included in the systematic review.

CONCLUSIONS

The review identifies significant effects of IRAK3 on decreasing NF-κB DNA binding activity in cell lines, TNF-α protein level at intermediate time intervals (4h-15h) in cell lines or at long term intervals (16h-48h) in mouse primary cells following one-challenge. The patterns of TNF-α protein expression in human cell lines and human primary cells in response to one-challenge are more similar than in mouse primary cells. Meta-analyses confirm a negative correlation between IRAK3 and inflammatory cytokine (IL-6 and TNF-α) expression after two-challenges.

Lipoteichoic acid of Enterococcus faecalis interferes with Porphyromonas gingivalis lipopolysaccharide signaling via IRAK-M upregulation in human periodontal ligament cells

Periodontitis is a chronic inflammatory disease of the gum caused by infection with multispecies oral bacteria. Since the periodontopathic bacteria, Porphyromonas gingivalis together with Enterococcus faecalis are frequently detected in patients with a severe form of periodontitis, interactions between their virulence factors might play an important role in progression of the disease. P. gingivalis and E. faecalis possess lipopolysaccharide (Pg.LPS) and lipoteichoic acid (Ef.LTA), respectively, as the major virulence factors inducing inflammatory responses. However, the combinatorial effect of these virulence factors on chemokine expression was poorly understood. Here, we examined the interaction between Ef.LTA and Pg.LPS on IL-8 induction in human periodontal ligament (PDL) cells. Pg.LPS, but not Ef.LTA, induced IL-8 expression at both mRNA and protein levels, which was suppressed in the presence of Ef.LTA. Although Ef.LTA and Pg.LPS could stimulate Toll-like receptor 2 (TLR2), Ef.LTA did not interfere with Pg.LPS induced-TLR2 activation. However, Ef.LTA decreased Pg.LPS-induced phosphorylation of ERK, JNK, and p38 kinase. Furthermore, Ef.LTA suppressed Pg.LPS-induced IL-8 promoter activity as well as AP-1, NF-IL6 and NF-κB transcription factors, which are indispensable for IL-8 expression. Interestingly, Ef.LTA enhanced only IL-1 receptor-associated kinase-M (IRAK-M) expression among the tested negative regulators of TLR intracellular signaling cascades in the presence of Pg.LPS. In addition, silencing IRAK-M restored the decreased IL-8 expression by Ef.LTA in the presence of Pg.LPS. Collectively, these results suggest that Ef.LTA inhibits Pg.LPS-induced IL-8 expression in human PDL cells via inducing the expression of a negative regulator of TLR signaling cascades, IRAK-M.

Protease-Activated Receptor 2 Facilitates Bacterial Dissemination in Pneumococcal Pneumonia

Streptococcus pneumoniae is the most common causative pathogen in community-acquired pneumonia. Protease-activated receptor 2 (PAR2) is expressed by different cell types in the lungs and can mediate inflammatory responses. We sought to determine the role of PAR2 during pneumococcal pneumonia. Pneumococcal pneumonia or sepsis was induced in wild-type and PAR2 knock-out (Par2-/-) mice by infection with viable S. pneumoniae. Par2-/- mice demonstrated improved host defense, a largely preserved lung barrier integrity, and reduced mortality during pneumococcal pneumonia. PAR2 deficiency did not influence bacterial growth after intravenous infection. Inhibition of the endogenous PAR2 activating proteases tissue factor/factor VIIa or tryptase did not impact on bacterial burdens during pneumonia. In a PAR2 reporter cell line it was demonstrated that S. pneumoniae-derived proteases are able to cleave PAR2. These results show that S. pneumoniae is able to cleave and exploit PAR2 to disseminate systemically from the airways.

Identification, characterisation and preliminary functional analysis of IRAK-M in grass carp (Ctenopharyngodon idella)

Interleukin-1 receptor-associated kinase (IRAK) family members play important roles in myeloid differentiation primary response 88 (MyD88)-dependent toll-like receptor (TLR) signaling, the crucial innate immune pathway in vertebrates. In the present study, the IRAK family gene IRAK-M (also called IRAK3) from grass carp (Ctenopharyngodon idella) was cloned and characterised. IRAK-M was mainly enriched in the spleen, and the significantly altered expression was observed after grass carp reovirus (GCRV) infection. Subcellular localisation showed that IRAK-M protein distributed uniformly in the entire cell and co-localised with MyD88 in the cytoplasm of transfected cells. Additionally, the interaction between IRAK-M and MyD88 was confirmed by bimolecular fluorescence complementation (BiFC) system. Moreover, deficient of IRAK-M in C. idella kidney cell line (CIK) with small interference RNA (siRNA) upregulated polyinosinic:polycytidylic acid (poly(I:C))-induced inflammatory cytokines production, including interleukin 8 (IL-8), IL-6, and tumour necrosis factor α (TNF-α), which reveals that IRAK-M functions as a negative regulator of inflammatory cytokines. Taken together, our results demonstrate that IRAK-M gene plays an important role in innate immune regulation and provide new insights into understanding the functional characteristics of the IRAK-M in teleosts.

Detrimental role for CCAAT/enhancer binding protein δ in blood-borne brain infection

Background

The most frequent pathogen that causes bacterial meningitis is the Gram-positive bacterium Streptococcus (S.) pneumoniae. CCAAT/enhancer binding protein δ is a transcription factor that has recently been hypothesized to play a detrimental role in outcome of meningitis caused by S. pneumoniae. Here, we studied the role of C/EBPδ prior to the development of pneumococcal meningitis.

Methods

Wild-type and C/EBPδ-deficient mice (C/EBPδ^−/−) were intraveneously infected with S. pneumoniae and sacrificed after 24 or 48 h. cebpδ expression, bacterial loads, inflammatory response and pathology in the brain were assessed.

Results

S. pneumoniae induces cebpδ expression in the brain during blood-borne brain infection. In comparison to wild-type mice, C/EBPδ^−/− animals showed decreased bacterial loads in blood and brain 48 h after inoculation. In the blood compartment, the host inflammatory response was significantly lower upon infection in C/EBPδ^−/− mice as compared to wild-type mice.

Conclusion

C/EBPδ facilitates bacterial dissemination to the brain and enhances the immune response in the blood compartment. Our study suggests that C/EBPδ plays a detrimental role during the initial development of blood-borne brain infection.

Activator protein 1 promotes the transcriptional activation of IRAK-M

Interleukin-1 receptor-associated kinase M (IRAK-M) is a well-known negative regulator for Toll-like receptor signaling, which can regulate immune homeostasis and tolerance in a number of pathological settings. However, the mechanism for IRAK-M regulation at transcriptional level remains largely unknown. In this study, a 1.4kb upstream sequence starting from the major IRAK-M transcriptional start site was cloned into luciferase reporter vector pGL3-basic to construct the full-length IRAK-M promoter. Luciferase reporter plasmids harboring the full-length and the deletion mutants of IRAK-M were transfected into 293T and A549 cells, and their relative luciferase activity was measured. The results demonstrated that activator protein 1(AP-1) cis-element plays a crucial role in IRAK-M constitutive gene transcription. Silencing of c-Fos and/or c-Jun expression suppressed the IRAK-M promoter activity as well as its mRNA and protein expressions. As a specific inhibitor for AP-1 activation, SP600125 also significantly suppressed the basal transcriptional activity of IRAK-M, the binding activity of c-Fos/c-Jun with IRAK-M promoter, and IRAK-M protein expression. Taken together, the result of this study highlights the importance of AP-1 in IRAK-M transcription, which offers more information on the role of IRAK-M in infectious and non-infectious diseases.

The gut microbiota plays a protective role in the host defence against pneumococcal pneumonia

OBJECTIVE

Pneumonia accounts for more deaths than any other infectious disease worldwide. The intestinal microbiota supports local mucosal immunity and is increasingly recognised as an important modulator of the systemic immune system. The precise role of the gut microbiota in bacterial pneumonia, however, is unknown. Here, we investigate the function of the gut microbiota in the host defence against Streptococcus pneumoniae infections.

DESIGN

We depleted the gut microbiota in C57BL/6 mice and subsequently infected them intranasally with S. pneumoniae. We then performed survival and faecal microbiota transplantation (FMT) experiments and measured parameters of inflammation and alveolar macrophage whole-genome responses.

RESULTS

We found that the gut microbiota protects the host during pneumococcal pneumonia, as reflected by increased bacterial dissemination, inflammation, organ damage and mortality in microbiota-depleted mice compared with controls. FMT in gut microbiota-depleted mice led to a normalisation of pulmonary bacterial counts and tumour necrosis factor-α and interleukin-10 levels 6 h after pneumococcal infection. Whole-genome mapping of alveolar macrophages showed upregulation of metabolic pathways in the absence of a healthy gut microbiota. This upregulation correlated with an altered cellular responsiveness, reflected by a reduced responsiveness to lipopolysaccharide and lipoteichoic acid. Compared with controls, alveolar macrophages derived from gut microbiota-depleted mice showed a diminished capacity to phagocytose S. pneumoniae.

CONCLUSIONS

This study identifies the intestinal microbiota as a protective mediator during pneumococcal pneumonia. The gut microbiota enhances primary alveolar macrophage function. Novel therapeutic strategies could exploit the gut-lung axis in bacterial infections.

The gut microbiota plays a protective role in the host defence against pneumococcal pneumonia

OBJECTIVE

Pneumonia accounts for more deaths than any other infectious disease worldwide. The intestinal microbiota supports local mucosal immunity and is increasingly recognised as an important modulator of the systemic immune system. The precise role of the gut microbiota in bacterial pneumonia, however, is unknown. Here, we investigate the function of the gut microbiota in the host defence against Streptococcus pneumoniae infections.

DESIGN

We depleted the gut microbiota in C57BL/6 mice and subsequently infected them intranasally with S. pneumoniae. We then performed survival and faecal microbiota transplantation (FMT) experiments and measured parameters of inflammation and alveolar macrophage whole-genome responses.

RESULTS

We found that the gut microbiota protects the host during pneumococcal pneumonia, as reflected by increased bacterial dissemination, inflammation, organ damage and mortality in microbiota-depleted mice compared with controls. FMT in gut microbiota-depleted mice led to a normalisation of pulmonary bacterial counts and tumour necrosis factor-α and interleukin-10 levels 6 h after pneumococcal infection. Whole-genome mapping of alveolar macrophages showed upregulation of metabolic pathways in the absence of a healthy gut microbiota. This upregulation correlated with an altered cellular responsiveness, reflected by a reduced responsiveness to lipopolysaccharide and lipoteichoic acid. Compared with controls, alveolar macrophages derived from gut microbiota-depleted mice showed a diminished capacity to phagocytose S. pneumoniae.

CONCLUSIONS

This study identifies the intestinal microbiota as a protective mediator during pneumococcal pneumonia. The gut microbiota enhances primary alveolar macrophage function. Novel therapeutic strategies could exploit the gut-lung axis in bacterial infections.

IRAK-M regulates the inhibition of TLR-mediated macrophage immune response during late in vitro Leishmania donovani infection

Intramacrophage protozoan parasite Leishmania donovani, causative agent of visceral leishmaniasis, escapes Toll-like receptor (TLR) dependent early host immune response by inducing the deubiquitinating enzyme A20, which is sustained up to 6 h postinfection only. Therefore, Leishmania must apply other means to deactivate late host responses. Here, we elucidated the role of IL-1 receptor-associated kinase M (IRAK-M), a negative regulator of TLR signaling, in downregulating macrophage proinflammatory response during late hours of in vitro infection. Our data reveal a sharp decline in IRAK1 and IRAK4 phosphorylation at 24 h postinfection along with markedly reduced association of IRAK1-TNF receptor associated factor 6, which is mandatory for TLR activation. In contrast, IRAK-M was induced after A20 levels decreased and reached a maximum at 24 h postinfection. IRAK-M induction coincided with increased stimulation of TGF-β, a hallmark cytokine of visceral infection. TGF-β-dependent signaling-mediated induction of SMAD family of proteins, 2, 3, and 4 plays important roles in transcriptional upregulation of IRAK-M. In infected macrophages, siRNA-mediated silencing of IRAK-M displayed enhanced IRAK1 and IRAK4 phosphorylation with a concomitant increase in downstream NF-κB activity and reduced parasite survival. Taken together, the results suggest that IRAK-M may be targeted by L. donovani to inhibit TLR-mediated proinflammatory response late during in vitro infection.

Enterococcus faecalis lipoteichoic acid suppresses Aggregatibacter actinomycetemcomitans lipopolysaccharide-induced IL-8 expression in human periodontal ligament cells

Periodontitis is caused by multi-bacterial infection and Aggregatibacter actinomycetemcomitans and Enterococcus faecalis are closely associated with inflammatory periodontal diseases. Although lipopolysaccharide (LPS) of A. actinomycetemcomitans (Aa.LPS) and lipoteichoic acid of E. faecalis (Ef.LTA) are considered to be major virulence factors evoking inflammatory responses, their combinatorial effect on the induction of chemokines has not been investigated. In this study, we investigated the interaction between Aa.LPS and Ef.LTA on IL-8 expression in human periodontal ligament (PDL) cells. Aa.LPS, but not Ef.LTA, substantially induced IL-8 expression at the protein and mRNA levels. Interestingly, Ef.LTA suppressed Aa.LPS-induced IL-8 expression without affecting the binding of Aa.LPS to Toll-like receptor (TLR) 4. Ef.LTA reduced Aa.LPS-induced phosphorylation of mitogen-activated protein kinases, including ERK, JNK and p38 kinase. Furthermore, Ef.LTA inhibited the Aa.LPS-induced transcriptional activities of the activating protein 1, CCAAT/enhancer-binding protein and nuclear factor-kappa B transcription factors, all of which are known to regulate IL-8 gene expression. Ef.LTA augmented the expression of IL-1 receptor-associated kinase-M (IRAK-M), a negative regulator of TLR intracellular signaling pathways, in the presence of Aa.LPS at both the mRNA and protein levels. Small interfering RNA silencing IRAK-M reversed the attenuation of Aa.LPS-induced IL-8 expression by Ef.LTA. Collectively, these results suggest that Ef.LTA down-regulates Aa.LPS-induced IL-8 expression in human PDL cells through up-regulation of the negative regulator IRAK-M.

Divergent functions of Toll-like receptors during bacterial lung infections

Lower respiratory tract infections caused by bacteria are a major cause of death in humans irrespective of sex, race, or geography. Indeed, accumulated data indicate greater mortality and morbidity due to these infections than cancer, malaria, or HIV infection. Successful recognition of, followed by an appropriate response to, bacterial pathogens in the lungs is crucial for effective pulmonary host defense. Although the early recruitment and activation of neutrophils in the lungs is key in the response against invading microbial pathogens, other sentinels, such as alveolar macrophages, epithelial cells, dendritic cells, and CD4(+) T cells, also contribute to the elimination of the bacterial burden. Pattern recognition receptors, such as Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain-like receptors, are important for recognizing and responding to microbes during pulmonary infections. However, bacterial pathogens have acquired crafty evasive strategies to circumvent the pattern recognition receptor response and thus establish infection. Increased understanding of the function of TLRs and evasive mechanisms used by pathogens during pulmonary infection will deepen our knowledge of immunopathogenesis and is crucial for developing effective therapeutic and/or prophylactic measures. This review summarizes current knowledge of the multiple roles of TLRs in bacterial lung infections and highlights the mechanisms used by pathogens to modulate or interfere with TLR signaling in the lungs.

Functional analysis of the uropathogenic Escherichia coli R049 gene

The objective of this study was to determine the function of the novel uropathogenic Escherichia coli (UPEC) gene R049 during host infection. We infected the urinary tracts of mice with E. coli UPEC132 or the R049 deletion mutant UPEC132ΔR049.The mouse kidneys were harvested at 4 and 8h post-infection and screened for differentially expressed genes by microarray analysis. We identified 379 and 515 differentially expressed genes at 4 and 8 h post-infection, respectively. Thirty-four of these genes were associated with inflammatory and immune signaling pathways, including those related to mitogen-activated protein kinase signaling, leukocyte transendothelial migration, cytokine-cytokine receptor interaction, Toll-like receptor signaling, and apoptosis. Protein binding (GO 0005515) was the most prevalent molecular function in the Gene Ontology terms related to differentially expressed genes. In conclusion, R049 expression in UPEC132 is related to the early innate immune and inflammatory responses in UPEC-infected hosts. This work lays the foundation for further research on anti-infective immunity against UPEC.

DNAX-activating protein of 12 kDa impairs host defense in pneumococcal pneumonia

OBJECTIVES

Streptococcus pneumoniae is the most common causative organism in community-acquired pneumonia responsible for millions of deaths every year. DNAX-activating protein of 12 kDa is an adaptor molecule for different myeloid expressed receptors involved in innate immunity.

DESIGN

Animal study.

SETTING

University research laboratory.

SUBJECTS

DNAX-activating protein of 12 kDa-deficient (dap12) and wild-type mice.

INTERVENTIONS

Mice were intranasally infected with S. pneumoniae. In addition, ex vivo responsiveness of alveolar macrophages was examined.

MEASUREMENTS AND MAIN RESULTS

dap12 alveolar macrophages released more tumor necrosis factor-α upon stimulation with S. pneumoniae and displayed increased phagocytosis of this pathogen compared with wild-type cells. After infection with S. pneumoniae via the airways, dap12 mice demonstrated reduced bacterial outgrowth in the lungs together with delayed dissemination to distant body sites relative to wild-type mice. This favorable response in dap12 mice was accompanied by reduced lung inflammation and an improved survival.

CONCLUSIONS

These data suggest that DNAX-activating protein of 12 kDa impairs host defense during pneumococcal pneumonia at the primary site of infection at least in part by inhibiting phagocytosis by alveolar macrophages.

Glucocorticoids suppress inflammation via the upregulation of negative regulator IRAK-M

Glucocorticoids are among the most commonly used anti-inflammatory agents. Despite the enormous efforts in elucidating the glucocorticoid-mediated anti-inflammatory actions, how glucocorticoids tightly control overactive inflammatory response is not fully understood. Here we show that glucocorticoids suppress bacteria-induced inflammation by enhancing IRAK-M, a central negative regulator of Toll-like receptor signalling. The ability of glucocorticoids to suppress pulmonary inflammation induced by non-typeable Haemophilus influenzae is significantly attenuated in IRAK-M-deficient mice. Glucocorticoids improve the survival rate after a lethal non-typeable Haemophilus influenzae infection in wild-type mice, but not in IRAK-M-deficient mice. Moreover, we show that glucocorticoids and non-typeable Haemophilus influenzae synergistically upregulate IRAK-M expression via mutually and synergistically enhancing p65 and glucocorticoid receptor binding to the IRAK-M promoter. Together, our studies unveil a mechanism by which glucocorticoids tightly control the inflammatory response and host defense via the induction of IRAK-M and may lead to further development of anti-inflammatory therapeutic strategies.

The structure function of the death domain of human IRAK-M

BACKGROUND

IRAK-M is an inhibitor of Toll-like receptor signaling that acts by re-directing IRAK-4 activity to TAK1 independent NF-κB activation and by inhibition of IRAK-1/IRAK-2 activity. IRAK-M is expressed in monocytes/macrophages and lung epithelial cells. Lack of IRAK-M in mice greatly improves the resistance to nosocomial pneumonia and lung tumors, which entices IRAK-M as a potential therapeutic target. IRAK-M consists of an N-terminal death domain (DD), a dysfunctional kinase domain and unstructured C-terminal domain. Little is known however on IRAK-M's structure-function relationships.

RESULTS

Since death domains provide the important interactions of IRAK-1, IRAK-2 and IRAK-4 molecules, we generated a 3D structure model of the human IRAK-M-DD (residues C5-G119) to guide mutagenesis studies and predict protein-protein interaction points. First we identified the DD residues involved in the endogenous capacity of IRAK-M to activate NF-κB that is displayed upon overexpression in 293T cells. W74 and R97, at distinct interfaces of the IRAK-M-DD, were crucial for this endogenous NF-κB activating capacity, as well as the C-terminal domain (S445-E596) of IRAK-M. Resulting anti-inflammatory A20 and pro-inflammatory IL-8 transcription in 293T cells was W74 dependent, while IL-8 protein expression was dependent on R97 and the TRAF6 binding motif at P478. The IRAK-M-DD W74 and R97 binding interfaces are predicted to interact with opposite sides of IRAK-4-DD's. Secondly we identified DD residues important for the inhibitory action of IRAK-M by stable overexpression of mutants in THP-1 macrophages and H292 lung epithelial cells. IRAK-M inhibited TLR2/4-mediated cytokine production in macrophages in a manner that is largely dependent on W74. R97 was not involved in inhibition of TNF production but was engaged in IL-6 down-regulation by IRAK-M. Protein-interactive residues D19-A23, located in between W74 and R97, were also observed to be crucial for inhibition of TLR2/4 mediated cytokine induction in macrophages. Remarkably, IRAK-M inhibited TLR5 mediated IL-8 production by lung epithelial cells independent of W74 and R97, but dependent on D19-A23 and R70, two surface-exposed regions that harbor predicted IRAK-2-DD interaction points of IRAK-M.

CONCLUSION

IRAK-M employs alternate residues of its DD to inhibit the different inflammatory mediators induced by varying TLRs and cells.

Role of interleukin 1 receptor like 1 (ST2) in gram-negative and gram-positive sepsis in mice

BACKGROUND

Interleukin 1 receptor-like 1 (ST2) has been implicated as a negative regulator of Toll-like receptor signaling. We here sought to elucidate the role of ST2 in cytokine release and systemic infection caused by two common human sepsis pathogens, Streptococcus pneumoniae (gram-positive) and Klebsiella pneumoniae (gram-negative).

METHODS

Whole blood leukocytes and splenocytes were harvested from ST2-deficient (st2) and wild-type (WT) mice and stimulated ex vivo with S. pneumoniae or K. pneumoniae. In addition, st2 and WT mice were infected intravenously with these bacteria, and bacterial loads and cytokine levels were measured in blood, spleens and lungs at 6, 24, and 48 h thereafter.

RESULTS

Unexpectedly, st2 blood leukocytes and splenocytes produced lower levels of cytokines and chemokines than WT cells in response to either pathogen. In contrast, the in vivo role of ST2 during sepsis caused by these bacteria was limited, although at 6 and 24 h after infection with S. pneumoniae bacterial loads were lower in spleens of st2 mice.

CONCLUSIONS

ST2 augments rather than inhibits cytokine release by blood leukocytes and splenocytes exposed to S. pneumoniae or K. pneumoniae, but plays a limited role in host defense during sepsis caused by these pathogens.

Single immunoglobulin interleukin-1 receptor-related molecule impairs host defense during pneumonia and sepsis caused by Streptococcus pneumoniae

Streptococcus pneumoniae is a common cause of pneumonia and sepsis. Toll-like receptors (TLRs) play a pivotal role in the host defense against infection. In this study, we sought to determine the role of single immunoglobulin interleukin-1 receptor-related molecule (SIGIRR a.k.a. TIR8), a negative regulator of TLR signaling, in pneumococcal pneumonia and sepsis. Wild-type and SIGIRR-deficient (sigirr-/-) mice were infected intranasally (to induce pneumonia) or intravenously (to induce primary sepsis) with S. pneumoniae and euthanized after 6, 24, or 48 h for analyses. Additionally, survival studies were performed. sigirr-/- mice showed delayed mortality during lethal pneumococcal pneumonia. Accordingly, sigirr-/- mice displayed lower bacterial loads in lungs and less dissemination of the infection 24 h after the induction of pneumonia. SIGIRR deficiency was associated with increased interstitial and perivascular inflammation in lung tissue early after infection, with no impact on neutrophil recruitment or cytokine production. sigirr-/- mice also demonstrated reduced bacterial burdens at multiple body sites during S. pneumoniae sepsis. sigirr-/- alveolar macrophages and neutrophils exhibited an increased capacity to phagocytose viable pneumococci. These results suggest that SIGIRR impairs the antibacterial host defense during pneumonia and sepsis caused by S. pneumoniae.

Bacterial interference with canonical NFκB signalling

The human body is constantly challenged by a variety of commensal and pathogenic micro-organisms that trigger the immune system. Central in the first line of defence is the pattern-recognition receptor (PRR)-induced stimulation of the NFκB pathway, leading to NFκB activation. The subsequent production of pro-inflammatory cytokines and/or antimicrobial peptides results in recruitment of professional phagocytes and bacterial clearance. To overcome this, bacteria have developed mechanisms for targeted interference in every single step in the PRR–NFκB pathway to dampen host inflammatory responses. This review aims to briefly overview the PRR–NFκB pathway in relation to the immune response and give examples of the diverse bacterial evasion mechanisms including changes in the bacterial surface, decoy production and injection of effector molecules. Targeted regulation of inflammatory responses is needed and bacterial molecules developed for immune evasion could provide future anti-inflammatory agents.

Limited role of the receptor for advanced glycation end products during Streptococcus pneumoniae bacteremia

Streptococcus pneumoniae is one of the most common causes of sepsis. Sepsis is associated with the release of 'damage-associated molecular patterns' (DAMPs). The receptor for advanced glycation end products (RAGE) is a multiligand receptor, abundantly expressed in the lungs, that recognizes several of these DAMPs. Triggering of RAGE leads to activation of the NF-κB pathway and perpetuation of inflammation. Earlier investigations have shown that the absence of RAGE reduces inflammation and bacterial dissemination and increases survival in sepsis caused by S. pneumoniae pneumonia. We hypothesized that the detrimental role of RAGE depends on the level of RAGE expression in the primary organ of infection. By directly injecting S. pneumoniae intravenously, thereby circumventing the extensive RAGE-expressing lung, we here determined whether RAGE contributes to an adverse outcome of bacteremia or whether its role is restricted to primary lung infection. During late-stage infection (48 h), rage(-/-) mice had an attenuated systemic inflammatory response, as reflected by lower plasma levels of proinflammatory cytokines, reduced endothelial cell activation (as measured by E-selectin levels) and less neutrophil accumulation in lung tissue. However, RAGE deficiency did not influence bacterial loads or survival in this model. In accordance, plasma markers for cell injury were similar in both mouse strains. These results demonstrate that while RAGE plays a harmful part in S. pneumoniae sepsis originating from the respiratory tract, this receptor has a limited role in the outcome of primary bloodstream infection by this pathogen.

IRAK-M expression limits dendritic cell activation and proinflammatory cytokine production in response to Helicobacter pylori

Helicobacter pylori (H. pylori) infects the gastric mucosa and persists for the life of the host. Bacterial persistence may be due to the induction of regulatory T cells (T_regs) whichmay have protective effects against other diseases such as asthma. It has been shown that H. pylori modulates the T cell response through dendritic cell reprogramming but the molecular pathways involved are relatively unknown. The goal of this study was to identify critical elements of dendritic cell (DC) activation and evaluate potential influence on immune activation. Microarray analysis was used to demonstrate limited gene expression changes in H. pylori stimulated bone marrow derived DCs (BMDCs) compared to the BMDCs stimulated with E. coli. IRAK-M, a negative regulator of TLR signaling, was upregulated and we selectedit for investigation of its role in modulating the DC and T cell responses. IRAK-M^−/− and wild type BMDC were compared for their response to H. pylori. Cells lacking IRAK-M produced significantly greater amounts of proinflammatory MIP-2 and reduced amounts of immunomodulatory IL-10 than wild type BMDC. IRAK-M^−/− cells also demonstrated increased MHC II expression upon activation. However, IRAK-M^−/− BMDCs were comparable to wild type BMDCs in inducing T-helper 17 (T_H17) and T_reg responses as demonstrated in vitro using BMDC CD4+ T cells co-culture assays,and in vivo though the adoptive transfer of CD4⁺ FoxP3-GFP T cells into H. pylori infected IRAK-M^−/− mice. These results suggest that H. pylori infection leads to the upregulation of anti-inflammatory molecules like IRAK-M and that IRAK-M has a direct impact on innate functions in DCs such as cytokine and costimulation molecule upregulation but may not affect T cell skewing.

Limited anti-inflammatory role for interleukin-1 receptor like 1 (ST2) in the host response to murine postinfluenza pneumococcal pneumonia

Interleukin-1 receptor like 1 (ST2) is a negative regulator of Toll-like receptor (TLR) signaling. TLRs are important for host defense during respiratory tract infections by both influenza and Streptococcus (S.) pneumoniae. Enhanced susceptibility to pneumococcal pneumonia is an important complication following influenza virus infection. We here sought to determine the role of ST2 in primary influenza A infection and secondary pneumococcal pneumonia. ST2 knockout (st2^−/−) and wild-type (WT) mice were intranasally infected with influenza A virus; in some experiments mice were infected 2 weeks later with S. pneumoniae. Both mouse strains cleared the virus similarly during the first 14 days of influenza infection and had recovered their weights equally at day 14. Overall st2^−/− mice tended to have a stronger pulmonary inflammatory response upon infection with influenza; especially 14 days after infection modest but statistically significant elevations were seen in lung IL-6, IL-1β, KC, IL-10, and IL-33 concentrations and myeloperoxidase levels, indicative of enhanced neutrophil activity. Interestingly, bacterial lung loads were higher in st2^−/− mice during the later stages of secondary pneumococcal pneumonia, which was associated with relatively increased lung IFN-γ levels. ST2 deficiency did not impact on gross lung pathology in either influenza or secondary S. pneumoniae pneumonia. These data show that ST2 plays a limited anti-inflammatory role during both primary influenza and postinfluenza pneumococcal pneumonia.