Mycobacterium tuberculosis Infection of Dendritic Cells Leads to Partially Caspase-1/11-Independent IL-1β and IL-18 Secretion but Not to Pyroptosis

Background

Interleukin-1β (IL-1β) is important for host resistance against Mycobacterium tuberculosis (Mtb) infections. The response of the dendritic cell inflammasome during Mtb infections has not been investigated in detail.

Methodology/Principal Findings

Here we show that Mtb infection of bone marrow-derived dendritic cells (BMDCs) induces IL-1β secretion and that this induction is dependent upon the presence of functional ASC and NLRP3 but not NLRC4 or NOD2. The analysis of cell death induction in BMDCs derived from these knock-out mice revealed the important induction of host cell apoptosis but not necrosis, pyroptosis or pyronecrosis. Furthermore, NLRP3 inflammasome activation and apoptosis induction were both reduced in BMDCs infected with the esxA deletion mutant of Mtb demonstrating the importance of a functional ESX-1 secretion system. Surprisingly, caspase-1/11-deficient BMDCs still secreted residual levels of IL-1βand IL-18 upon Mtb infection which was abolished in cells infected with the esxA Mtb mutant.

Conclusion

Altogether we demonstrate the partially caspase-1/11-independent, but NLRP3- and ASC- dependent IL-1β secretion in Mtb-infected BMDCs. These findings point towards a potential role of DCs in the host innate immune response to mycobacterial infections via their capacity to induce IL-1β and IL-18 secretion.     

Strong immunogenicity and cross-reactivity of Mycobacterium tuberculosis ESX-5 type VII secretion: encoded PE-PPE proteins predicts vaccine potential

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Highlights? Mtb ESX-5-associated and -nonassociated PE/PPE proteins are highly immunogenic ? ESX-5 core component eccD₅ modulates the mycobacterial antigenic repertoire ? ESX-5 PE/PPE deleted Δppe25-pe19 Mtb strain is avirulent, yet strongly immunogenic ? Δppe25-pe19 strain protects mice against Mtb infection and represents a vaccine candidate     

Experimental tuberculosis in the Wistar rat: a model for protective immunity and control of infection

Background

Despite the availability of many animal models for tuberculosis (TB) research, there still exists a need for better understanding of the quiescent stage of disease observed in many humans. Here, we explored the use of the Wistar rat model for the study of protective immunity and control of Mycobacterium tuberculosis (Mtb) infection.

Methodology/Principal Findings

The kinetics of bacillary growth, evaluated by the colony stimulating assay (CFU) and the extent of lung pathology in Mtb infected Wistar rats were dependent on the virulence of the strains and the size of the infecting inoculums. Bacillary growth control was associated with induction of T helper type 1 (Th1) activation, the magnitude of which was also Mtb strain and dose dependent. Histopathology analysis of the infected lungs demonstrated the formation of well organized granulomas comprising epithelioid cells, multinucleated giant cells and foamy macrophages surrounded by large numbers of lymphocytes. The late stage subclinical form of disease was reactivated by immunosuppression leading to increased lung CFU.

Conclusion

The Wistar rat is a valuable model for better understanding host-pathogen interactions that result in control of Mtb infection and potentially establishment of latent TB. These properties together with the ease of manipulation, relatively low cost and well established use of rats in toxicology and pharmacokinetic analyses make the rat a good animal model for TB drug discovery.     

Lipid metabolism and Type VII secretion systems dominate the genome scale virulence profile of Mycobacterium tuberculosis in human dendritic cells

Background

Mycobacterium tuberculosis continues to kill more people than any other bacterium. Although its archetypal host cell is the macrophage, it also enters, and survives within, dendritic cells (DCs). By modulating the behaviour of the DC, M. tuberculosis is able to manipulate the host’s immune response and establish an infection. To identify the M. tuberculosis genes required for survival within DCs we infected primary human DCs with an M. tuberculosis transposon library and identified mutations with a reduced ability to survive.

Results

Parallel sequencing of the transposon inserts of the surviving mutants identified a large number of genes as being required for optimal intracellular fitness in DCs. Loci whose mutation attenuated intracellular survival included those involved in synthesising cell wall lipids, not only the well-established virulence factors, pDIM and cord factor, but also sulfolipids and PGL, which have not previously been identified as having a direct virulence role in cells. Other attenuated loci included the secretion systems ESX-1, ESX-2 and ESX-4, alongside many PPE genes, implicating a role for ESX-5. In contrast the canonical ESAT-6 family of ESX substrates did not have intra-DC fitness costs suggesting an alternative ESX-1 associated virulence mechanism. With the aid of a gene-nutrient interaction model, metabolic processes such as cholesterol side chain catabolism, nitrate reductase and cysteine-methionine metabolism were also identified as important for survival in DCs.

Conclusion

We conclude that many of the virulence factors required for survival in DC are shared with macrophages, but that survival in DCs also requires several additional functions, such as cysteine-methionine metabolism, PGLs, sulfolipids, ESX systems and PPE genes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1569-2) contains supplementary material, which is available to authorized users.     

Molecular Epidemiology and Clinical Characteristics of Drug-Resistant Mycobacterium tuberculosis in a Tuberculosis Referral Hospital in China

Background

Despite the large number of drug-resistant tuberculosis (TB) cases in China, few studies have comprehensively analyzed the drug resistance-associated gene mutations and genotypes in relation to the clinical characteristics of M. tuberculosis (Mtb) isolates.

Methodology/Principal Findings

We thus analyzed the phenotypic and genotypic drug resistance profiles of 115 Mtb clinical isolates recovered from a tuberculosis referral hospital in Beijing, China. We also performed genotyping by 28 loci MIRU-VNTR analysis. Socio-demographic and clinical data were retrieved from medical records and analyzed. In total, 78 types of mutations (including 42 previously reported and 36 newly identified ones) were identified in 115 Mtb clinical isolates. There was significant correlation between phenotypic and genotypic drug resistance rates for first-line anti-TB drugs (P<0.001). Genotyping revealed 101 MIRU-VNTR types, with 20 isolates (17.4%) being clustered and 95 isolates (82.6%) having unique genotypes. Higher proportion of re-treatment cases was observed among patients with clustered isolates than those with unique MIRU-VNTR genotypes (75.0% vs. 41.1%). Moreover, clinical epidemiological links were identified among patients infected by Mtb strains belonging to the same clusters, suggesting a potential of transmission among patients.

Conclusions/Significance

Our study provided information on novel potential drug resistance-associated mutations in Mtb. In addition, the genotyping data from our study suggested that enforcement of the implementation of genotyping in diagnostic routines would provide important information for better monitor and control of TB transmission.     

Membrane TNF confers protection to acute mycobacterial infection

Background

Tumour necrosis factor (TNF) is crucial for the control of mycobacterial infection as TNF deficient (KO) die rapidly of uncontrolled infection with necrotic pneumonia. Here we investigated the role of membrane TNF for host resistance in knock-in mice with a non-cleavable and regulated allele (mem-TNF).

Methods

C57BL/6, TNF KO and mem-TNF mice were infected with M. tuberculosis H37Rv (Mtb at 100 CFU by intranasal administration) and the survival, bacterial load, lung pathology and immunological parameters were investigated. Bone marrow and lymphocytes transfers were used to test the role of membrane TNF to confer resistance to TNF KO mice.

Results

While TNF-KO mice succumbed to infection within 4–5 weeks, mem-TNF mice recruited normally T cells and macrophages, developed mature granuloma in the lung and controlled acute Mtb infection. However, during the chronic phase of infection mem-TNF mice succumbed to disseminated infection with necrotic pneumonia at about 150 days. Reconstitution of irradiated TNF-KO mice with mem-TNF derived bone marrow cells, but not with lymphocytes, conferred host resistance to Mtb infection in TNF-KO mice.

Conclusion

Membrane expressed TNF is sufficient to allow cell-cell signalling and control of acute Mtb infection. Bone marrow cells, but not lymphocytes from mem-TNF mice confer resistance to infection in TNF-KO mice. Long-term infection control with chronic inflammation likely disrupting TNF mediated cell-cell signalling, additionally requires soluble TNF.     

Endoplasmic reticulum stress pathway-mediated apoptosis in macrophages contributes to the survival of Mycobacterium tuberculosis

Background

Apoptosis is thought to play a role in host defenses against intracellular pathogens, including Mycobacterium tuberculosis (Mtb), by preventing the release of intracellular components and the spread of mycobacterial infection. This study aims to investigate the role of endoplasmic reticulum (ER) stress mediated apoptosis in mycobacteria infected macrophages.

Methodology/Principal Findings

Here, we demonstrate that ER stress-induced apoptosis is associated with Mtb H37Rv-induced cell death of Raw264.7 murine macrophages. We have shown that Mtb H37Rv induced apoptosis are involved in activation of caspase-12, which resides on the cytoplasmic district of the ER. Mtb infection increase levels of other ER stress indicators in a time-dependent manner. Phosphorylation of eIF2α was decreased gradually after Mtb H37Rv infection signifying that Mtb H37Rv infection may affect eIF2α phosphorylation in an attempt to survive within macrophages. Interestingly, the survival of mycobacteria in macrophages was enhanced by silencing CHOP expression. In contrast, survival rate of mycobacteria was reduced by phosphorylation of the eIF2α. Futhermore, the levels of ROS, NO or CHOP expression were significantly increased by live Mtb H37Rv compared to heat-killed Mtb H37Rv indicating that live Mtb H37Rv could induce ER stress response.

Conclusion/Significance

These findings indicate that eIF2α/CHOP pathway may influence intracellular survival of Mtb H37Rv in macrophages and only live Mtb H37Rv can induce ER stress response. The data support the ER stress pathway plays an important role in the pathogenesis and persistence of mycobacteria.     

IFN-γ plays a unique role in protection against low virulent Trypanosoma cruzi strain

Background

T. cruzi strains have been divided into six discrete typing units (DTUs) according to their genetic background. These groups are designated T. cruzi I to VI. In this context, amastigotes from G strain (T. cruzi I) are highly infective in vitro and show no parasitemia in vivo. Here we aimed to understand why amastigotes from G strain are highly infective in vitro and do not contribute for a patent in vivo infection.

Methodology/Principal Findings

Our in vitro studies demonstrated the first evidence that IFN-γ would be associated to the low virulence of G strain in vivo. After intraperitoneal amastigotes inoculation in wild-type and knockout mice for TNF-α, Nod2, Myd88, iNOS, IL-12p40, IL-18, CD4, CD8 and IFN-γ we found that the latter is crucial for controlling infection by G strain amastigotes.

Conclusions/Significance

Our results showed that amastigotes from G strain are highly infective in vitro but did not contribute for a patent infection in vivo due to its susceptibility to IFN-γ production by host immune cells. These data are useful to understand the mechanisms underlying the contrasting behavior of different T. cruzi groups for in vitro and in vivo infection.     

Loss of a single N-linked glycan from the hemagglutinin of influenza virus is associated with resistance to collectins and increased virulence in mice

Background

Glycosylation on the globular head of the hemagglutinin (HA) protein of influenza virus acts as an important target for recognition and destruction of virus by innate immune proteins of the collectin family. This, in turn, modulates the virulence of different viruses for mice. The role of particular oligosaccharide attachments on the HA in determining sensitivity to collectins has yet to be fully elucidated.

Methods

When comparing the virulence of H3N2 subtype viruses for mice we found that viruses isolated after 1980 were highly glycosylated and induced mild disease in mice. During these studies, we were surprised to find a small plaque variant of strain A/Beijing/353/89 (Beij/89) emerged following infection of mice and grew to high titres in mouse lung. In the current study we have characterized the properties of this small plaque mutant both in vitro and in vivo.

Results

Small plaque mutants were recovered following plaquing of lung homogenates from mice infected with influenza virus seed Beij/89. Compared to wild-type virus, small plaque mutants showed increased virulence in mice yet did not differ in their ability to infect or replicate in airway epithelial cells in vitro. Instead, small plaque variants were markedly resistant to neutralization by murine collectins, a property that correlated with the acquisition of an amino acid substitution at residue 246 on the viral HA. We present evidence that this substitution was associated with the loss of an oligosaccharide glycan from the globular head of HA.

Conclusion

A point mutation in the gene encoding the HA of Beij/89 was shown to ablate a glycan attachment site. This was associated with resistance to collectins and increased virulence in mice.     

Umbilical Cord Blood IL-6 as Predictor of Early-Onset Neonatal Sepsis in Women with Preterm Prelabour Rupture of Membranes

Objective

To evaluate umbilical cord interleukin (IL)-6 and funisitis as independent predictors of early-onset neonatal sepsis (EONS) in preterm prelabor rupture of membranes (PPROM).

Design

Prospective cohort study.

Setting

Evaluation of umbilical cord IL-6 and funisitis as predictors of early-onset neonatal sepsis in PPROM.

Population

176 women with PPROM between 23+0−36+6 weeks of gestation.

Methods

Umbilical cord IL-6 was assayed by ELISA. Funisitis was defined according to the Salafia classification. Data was adjusted by gestational age at delivery and prenatal administration of corticosteroids and antibiotics.

Main Outcome Measures

Binary logistic regression was performed to assess the independence of umbilical cord IL-6 and funisitis to predict EONS in women complicated with PPROM.

Results

The rate of EONS was 7%. Funisitis was present in 18% of women. Umbilical cord IL-6 was significantly higher in women complicated with EONS than without [median (range) 389.5 pg/mL (13.9–734.8) vs 5.2 (0.1–801–4), p<0.001]. Umbilical cord IL-6 was the only independent predictor of early-onset neonatal sepsis (odds ratio 13.6, p = 0.004).

Conclusion

Umbilical cord IL-6 was the only predictor of early-onset neonatal sepsis in PPROM. Contrary to what is reported, funisitis was not.     

Serum Interleukin-18 Levels Are Associated with Physical Activity in Japanese Men

Objective

To investigate the link between serum interleukin-18 (IL-18) levels and physical activity in Japanese men.

Methods

A total of 81 men (45.7±17.6 years old) was enrolled in this cross-sectional investigation study. We assessed anthropometric and body composition parameters. Serum IL-18 levels, physical activity by uniaxial accelerometers, peak oxygen uptake and metabolic risk parameters were also evaluated.

Results

Serum IL-18 levels were 179.4±84.7 pg/mL. Physical activity evaluated by Σ[metabolic equivalents × h per week (METs⋅h/w)]was significantly and negatively correlated with serum IL-18 levels (r = −0.252, p = 0.0235). These associations remained even after adjusting for age, peak oxygen uptake and other confounding factors.

Conclusion

Serum IL-18 levels were closely associated with physical activity independent of peak oxygen uptake in Japanese men.     

The Balance of Apoptotic and Necrotic Cell Death in Mycobacterium tuberculosis Infected Macrophages Is Not Dependent on Bacterial Virulence

Background

An important mechanism of Mycobacterium tuberculosis pathogenesis is the ability to control cell death pathways in infected macrophages: apoptotic cell death is bactericidal, whereas necrotic cell death may facilitate bacterial dissemination and transmission.

Methods

We examine M.tuberculosis control of spontaneous and chemically induced macrophage cell death using automated confocal fluorescence microscopy, image analysis, flow cytometry, plate-reader based vitality assays, and M.tuberculosis strains including H37Rv, and isogenic virulent and avirulent strains of the Beijing lineage isolate GC1237.

Results

We show that bacterial virulence influences the dynamics of caspase activation and the total level of cytotoxicity. We show that the powerful ability of M.tuberculosis to inhibit exogenously stimulated apoptosis is abrogated by loss of virulence. However, loss of virulence did not influence the balance of macrophage apoptosis and necrosis – both virulent and avirulent isogenic strains of GC1237 induced predominantly necrotic cell death compared to H37Rv which induced a higher relative level of apoptosis.

Conclusions

This reveals that macrophage necrosis and apoptosis are independently regulated during M. tuberculosis infection of macrophages. Virulence affects the level of host cell death and ability to inhibit apoptosis but other strain-specific characteristics influence the ultimate mode of host cell death and alter the balance of apoptosis and necrosis.     

Prevalence and Clinical Course in Invasive Infections with Meningococcal Endotoxin Variants

Background

Meningococci produce a penta-acylated instead of hexa-acylated lipid A when their lpxL1 gene is inactivated. Meningococcal strains with such lipid A endotoxin variants have been found previously in adult meningitis patients, where they caused less blood coagulopathy because of decreased TLR4 activation.

Methods

A cohort of 448 isolates from patients with invasive meningococcal disease in the Netherlands were screened for the ability to induce IL-6 in monocytic cell Mono Mac 6 cells. The lpxL1 gene was sequenced of isolates, which show poor capacity to induce IL-6.. Clinical characteristics of patients were retrieved from hospital records.

Results

Of 448 patients, 29 (6.5%) were infected with meningococci expressing a lipid A variant strain. Lipid A variation was not associated with a specific serogroup or genotype. Infections with lipid A variants were associated with older age (19.3 vs. 5.9 (median) years, p = 0.007) and higher prevalence of underlying comorbidities (39% vs. 17%; p = 0.004) compared to wild-type strains. Patients infected with lipid A variant strains had less severe infections like meningitis or shock (OR 0.23; 95%CI 0.09–0.58) and were less often admitted to intensive care (OR 0.21; 95%CI 0.07–0.60) compared to wild-type strains, independent of age, underlying comorbidities or strain characteristics.

Conclusions

In adults with meningococcal disease lipid A variation is rather common. Infection with penta-acylated lipid A variant meningococci is associated with a less severe disease course.     

Modern Lineages of Mycobacterium tuberculosis Exhibit Lineage-Specific Patterns of Growth and Cytokine Induction in Human Monocyte-Derived Macrophages

Background

Strains of Mycobacterium tuberculosis vary in virulence. Strains that have caused outbreaks in the United States and United Kingdom have been shown to subvert the innate immune response as a potential immune evasion mechanism. There is, however, little information available as to whether these patterns of immune subversion are features of individual strains or characteristic of broad clonal lineages of M. tuberculosis.

Methods

Strains from two major modern lineages (lineage 2 [East-Asian] and lineage 4 [Euro-American]) circulating in the Western Cape in South Africa as well as a comparator modern lineage (lineage 3 [CAS/Delhi]) were identified. We assessed two virulence associated characteristics: mycobacterial growth (in liquid broth and monocyte derived macrophages) and early pro-inflammatory cytokine induction.

Results

In liquid culture, Lineage 4 strains grew more rapidly and reached higher plateau levels than other strains (lineage 4 vs. lineage 2 p = 0.0024; lineage 4 vs. lineage 3 p = 0.0005). Lineage 3 strains were characterized by low and early plateau levels, while lineage 2 strains showed an intermediate growth phenotype. In monocyte-derived macrophages, lineage 2 strains grew faster than lineage 3 strains (p<0.01) with lineage 4 strains having an intermediate phenotype. Lineage 2 strains induced the lowest levels of pro-inflammatory TNF and IL-12p40 as compared to other lineages (lineage 2: median TNF 362 pg/ml, IL-12p40 91 pg/ml; lineage 3: median TNF 1818 pg/ml, IL-12p40 123 pg/ml; lineage 4: median TNF 1207 pg/ml, IL-12p40 205 pg/ml;). In contrast, lineage 4 strains induced high levels of IL-12p40 and intermediate level of TNF. Lineage 3 strains induced high levels of TNF and intermediate levels of IL-12p40.

Conclusions

Strains of M. tuberculosis from the three major modern strain lineages possess distinct patterns of growth and cytokine induction. Rapid growth and immune subversion may be key characteristics to the success of these strains in different human populations.     

Comparative genomics between human and animal associated subspecies of the Mycobacterium avium complex: a basis for pathogenicity

Background

A human isolate of Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis 43525) was sequenced and compared genomically to other mycobacterial pathogens. M. paratuberculosis 43525 was recently isolated from a patient with ulcerative colitis and belongs to the M. avium complex, a group known to infect both humans and animals. While M. paratuberculosis is a known pathogen of livestock, there are only 20 human isolates from the last 20 years, therefore we took the opportunity to perform a whole genome comparison between human and animal mycobacterial pathogens. We also compared virulence determinants such as the mycobactin cluster, PE/PPE genes and mammalian cell entry (mce) operons between MAC subspecies that infect animals and those that infect humans. M. tuberculosis was also included in these analyses given its predominant role as a human pathogen.

Results

This genome comparison showed the PE/PPE profile of M. paratuberculosis 43525 to be largely the same as other M. paratuberculosis isolates, except that it had one PPE and one PE_PGRS protein that are only present in human MAC strains and M. tuberculosis. PE/PPE proteins that were unique to M. paratuberculosis 43525, M. avium subsp. hominissuis and a caprine M. paratuberculosis isolate, were also identified. In addition, the mycobactin cluster differed between human and animal isolates and a unique mce operon flanked by two mycobactin genes, mbtA and mbtJ, was identified in all available M. paratuberculosis genomes.

Conclusions

Despite the whole genome comparison placing M. paratuberculosis 43525 as closely related to bovine M. paratuberculosis, key virulence factors were similar to human mycobacterial pathogens. This study highlights key factors of mycobacterial pathogenesis in humans and forms the basis for future functional studies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1889-2) contains supplementary material, which is available to authorized users.     

Elevated expression of both mRNA and protein levels of IL-17A in sputum of stable Cystic Fibrosis patients

Background

T helper 17 (Th17) cells can recruit neutrophils to inflammatory sites through production of IL-17, which induces chemokine release. IL-23 is an important inducer of IL-17 and IL-22 production. Our aim was to study the role of Th17 cells in cystic fibrosis (CF) lung disease by measuring IL-17 protein and mRNA levels and IL-22 and IL-23 mRNA in sputum of clinically stable CF patients and by comparing these levels with healthy controls.

Methods

Sputum induction was performed in adult CF patients outside of an exacerbation and healthy control subjects. IL-17A protein levels were measured in supernatants with cytometric bead array (CBA) and RNA was isolated and quantitative RT-PCR was performed for IL-17A, IL-22 and IL-23.

Results

We found significantly higher levels of IL-17A protein and mRNA levels (both: p < 0.0001) and IL-23 mRNA levels (p < 0.0001) in the sputum of CF group as compared to controls. We found very low levels of IL-22 mRNA in the CF group. The levels of IL-17 and IL-23 mRNA were higher in patients chronically infected with Pseudomonas aeruginosa (P. aeruginosa) as compared to those who were not chronically infected with P. aeruginosa. The presence of Staphylococcus aureus (S. aureus) on sputum did not affect the IL-17 or IL-23 levels. There was no correlation between IL-17 or IL-23 levels and FEV₁ nor sputum neutrophilia.

Conclusion

The elevated levels of IL-17 and IL-23 might indicate that Th17 cells are implicated in the persistent neutrophil infiltration in CF lung disease and chronic infection with P. aeruginosa.     

Lean body mass, interleukin 18, and metabolic syndrome in apparently healthy Chinese

Objective

We aimed to investigate how lean body mass is related to circulating Interleukin 18 (IL-18) and its association with metabolic syndrome (MetS) among apparently healthy Chinese.

Methods

A population-based sample of 1059 Chinese men and women aged 35–54 years was used to measure plasma IL-18, glucose, insulin, lipid profile, inflammatory markers and high-molecular-weight (HMW)-adiponectin. Fat mass index (FMI) and lean mass index (LMI) were measured by dual-energy X-ray absorptiometry. MetS was defined by the updated National Cholesterol Education Program Adult Treatment Panel III criteria for Asian-Americans.

Results

Circulating IL-18 was positively correlated with LMI after adjustment for FMI (correlation coefficient = 0.11, P<0.001). The association with the MetS (odds ratio 3.43, 95% confidence interval 2.01–5.85) was substantially higher in the highest than the lowest quartile of IL-18 after multiple adjustments including body mass index. In the stratified multivariable regression analyses, the positive association between IL-18 and MetS was independent of tertiles of FMI, inflammatory markers and HMW-adiponectin, but significantly interacted with tertile of LMI (P for interaction = 0.010).

Conclusion

Elevated plasma IL-18 was associated with higher MetS prevalence in apparently healthy Chinese, independent of traditional risk factors, FMI, inflammatory markers and HMW-adiponectin. More studies are needed to clarify the role of lean mass in IL-18 secretion and its associated cardio-metabolic disorders.     

The role of IL-27 in susceptibility to post-influenza Staphylococcus aureus pneumonia

Background

Influenza is a common respiratory virus and Staphylococcus aureus frequently causes secondary pneumonia during influenza infection, leading to increased morbidity and mortality. Influenza has been found to attenuate subsequent Type 17 immunity, enhancing susceptibility to secondary bacterial infections. IL-27 is known to inhibit Type 17 immunity, suggesting a potential critical role for IL-27 in viral and bacterial co-infection.

Methods

A murine model of influenza and Staphylococcus aureus infection was used to mimic human viral, bacterial co-infection. C57BL/6 wild-type, IL-27 receptor α knock-out, and IL-10 knock-out mice were infected with Influenza H1N1 (A/PR/8/34) or vehicle for 6 days followed by challenge with Staphylococcus aureus or vehicle for 24 hours. Lung inflammation, bacterial burden, gene expression, and cytokine production were determined.

Results

IL-27 receptor α knock-out mice challenged with influenza A had increased morbidity compared to controls, but no change in viral burden. IL-27 receptor α knock-out mice infected with influenza displayed significantly decreased IL-10 production compared to wild-type. IL-27 receptor α knock-out mice co-infected with influenza and S. aureus had improved bacterial clearance compared to wild-type controls. Importantly, there were significantly increased Type 17 responses and decreased IL-10 production in IL-27 receptor α knock-out mice. Dual infected IL-10−/− mice had significantly less bacterial burden compared to dual infected WT mice.

Conclusions

These data reveal that IL-27 regulates enhanced susceptibility to S. aureus pneumonia following influenza infection, potentially through the induction of IL-10 and suppression of IL-17.     

Difference in virulence of Mycobacterium avium isolates sharing indistinguishable DNA fingerprint determined in murine model of lung infection

Background

Opportunistic Mycobacterium avium typically causes disease in immunocompromised patients and in some groups of apparently healthy individuals. The high virulence of some bacterial lineages increases the disease risk. High-resolution molecular genotyping studies of M. avium clinical isolates demonstrated that some genotype patterns were more prevalent than others, suggesting that close genetic relatedness of these successful isolates sharing a similar genotype could determine similar biological properties associated with high virulence.

Methods and Findings

In this study, we aimed to compare the virulence and pathogenic properties of two epidemiologically unrelated M. avium isolates sharing an indistinguishable DNA fingerprint in a well-characterized model of pulmonary infection in mice, resistant or susceptible to mycobacteria. The mice, C57BL/6 wild- type or IFN-gamma gene disrupted (GKO), respectively, were intratracheally infected with two isolates, H27 (human blood isolate) and P104 (pig lymph node isolate), and the lungs were examined for bacterial loads, histopathology and cytokine gene expression. The obtained data demonstrated significant differences in the virulence properties of these strains. Although the H27 strain grew significantly faster than P104 in the early stage of infection, this bacterium induced protective immunity that started to reduce bacterial numbers in the wild- type mice, whereas the P104 strain established a chronic infection. In the GKO mice, both strains were capable of causing a chronic infection, associated with higher bacterial burdens and severe lung pathology, in a similar manner.

Conclusions/Significance

The results demonstrated that the studied isolates differed in the pathogenic properties although were indistinguishable by actually widely used genotyping techniques demonstrating that the genotype similarity does not predict similarity in virulence of M. avium isolates.