Heme oxygenase-1 inhibition promotes IFNγ- and NOS2-mediated control of Mycobacterium tuberculosis infection

Mycobacterium tuberculosis (Mtb) infection induces pulmonary expression of the heme-degrading enzyme heme oxygenase-1 (HO-1). We have previously shown that pharmacological inhibition of HO-1 activity in experimental tuberculosis results in decreased bacterial loads and unexpectedly that this outcome depends on the presence of T lymphocytes. Here, we extend these findings by demonstrating that IFNγ production by T lymphocytes and NOS2 expression underlie this T-cell requirement and that HO-1 inhibition potentiates IFNγ-induced NOS2-dependent control of Mtb by macrophages in vitro. Among the products of heme degradation by HO-1 (biliverdin, carbon monoxide, and iron), only iron supplementation reverted the HO-1 inhibition-induced enhancement of bacterial control and this reversal was associated with decreased NOS2 expression and NO production. In addition, we found that HO-1 inhibition results in decreased labile iron levels in Mtb-infected macrophages in vitro and diminished iron accumulation in Mtb-infected lungs in vivo. Together these results suggest that the T-lymphocyte dependence of the therapeutic outcome of HO-1 inhibition on Mtb infection reflects the role of the enzyme in generating iron that suppresses T-cell-mediated IFNγ/NOS2-dependent bacterial control. In broader terms, our findings highlight the importance of the crosstalk between iron metabolism and adaptive immunity in determining the outcome of infection.

Mycobacterium tuberculosis-specific CD4 T cells expressing CD153 inversely associate with bacterial load and disease severity in human tuberculosis

Recent data from mice and non-human primate models of tuberculosis suggested that CD153, a TNF super family member, plays an important role in Mycobacterium tuberculosis (Mtb) control. However, this molecule has not been comprehensively evaluated in humans. Here, we show that the proportion of Mtb-specific CD4 T cells expressing CD153 was significantly reduced in active TB patients compared to latently infected persons. Importantly, the CD153+ Mtb-specific CD4 response inversely correlated with lung bacterial load, inferred by Xpert cycle threshold, irrespective of HIV status. Antitubercular treatment partially restored CD153 expression on Mtb-specific CD4 T cells. This is the first report of a subset of Mtb-specific CD4 T cells showing strong negative correlation with bacterial burden. Building on substantial evidence from animal models implicating CD153 as a mediator of host protection, our findings suggest it may play a similar role in humans and its measurement may be useful to evaluate TB vaccine efficacy.

A Long-Acting Thermoresponsive Injectable Formulation of Tin Protoporphyrin Sustains Antitubercular Efficacy in a Murine Infection Model

Tuberculosis is the leading cause of death from a single infectious agent, ranking above the human immunodeficiency virus (HIV). Effective treatment using antibiotics is achievable, but poor patient compliance constitutes a major challenge impeding successful pharmacotherapeutic outcomes. This is often due to the prolonged treatment periods required and contributes significantly to the rising incidence of drug resistance, which is a major cause of tuberculosis mortality. Thus, innovative interventions capable of encouraging compliance and decreasing lengthy and frequent dosing are needed. Previously, aqueous tin protoporphyrin IX (SnPPIX), a heme oxygenase-1 inhibitor, administered as multiple daily intraperitoneal (IP) injections, showed considerable antitubercular efficacy and treatment shortening capabilities as a host-directed therapy in infected mice. Since daily IP injection is a clinically impractical administration approach, this proof-of-concept study aims to develop a novel, sustained action injectable formulation of SnPPIX for safe intramuscular (IM) administration. Herein, a SnPPIX-loaded poloxamer-poly(acrylic acid)-based thermoresponsive injectable formulation (SnPPIX-TIF) is designed for effective IM delivery. Results show SnPPIX-TIF is microparticulate, syringeable, injectable, and exhibits complete in vitro/in vivo gelation. Administered once weekly, SnPPIX-TIF significantly prolonged absorption and antimicrobial efficacy in infected mice. In addition, SnPPIX-TIF is well-tolerated in vivo; results from treated animals show no significant histopathologic alterations and were indistinguishable from the untreated control group, thus supporting its biocompatibility and preclinical safety. Overall, the IM delivery of the thermoresponsive injectable formulation safely sustains antitubercular effect in an infected murine model and decreases the number of injections required, signifying a potentially practical approach for future clinical translation.

Modulation of Inflammation and Immune Responses by Heme Oxygenase-1: Implications for Infection with Intracellular Pathogens

Heme oxygenase-1 (HO-1) catalyzes the degradation of heme molecules releasing equimolar amounts of biliverdin, iron and carbon monoxide. Its expression is induced in response to stress signals such as reactive oxygen species and inflammatory mediators with antioxidant, anti-inflammatory and immunosuppressive consequences for the host. Interestingly, several intracellular pathogens responsible for major human diseases have been shown to be powerful inducers of HO-1 expression in both host cells and in vivo. Studies have shown that this HO-1 response can be either host detrimental by impairing pathogen control or host beneficial by limiting infection induced inflammation and tissue pathology. These properties make HO-1 an attractive target for host-directed therapy (HDT) of the diseases in question, many of which have been difficult to control using conventional antibiotic approaches. Here we review the mechanisms by which HO-1 expression is induced and how the enzyme regulates inflammatory and immune responses during infection with a number of different intracellular bacterial and protozoan pathogens highlighting mechanistic commonalities and differences with the goal of identifying targets for disease intervention.

Comparison of perinatal outcomes for all modes of second stage delivery in obstetric theatres: a retrospective observational study

OBJECTIVE

To compare rates of vaginal delivery and adverse outcomes of instrumental delivery trials in obstetric theatre compared to primary emergency full dilation caesarean section.

DESIGN

Retrospective cohort study.

SETTING

University teaching hospital.

POPULATION

Women with singleton, non-anomalous, pregnancy undergoing instrumental delivery trial in obstetric theatre.

METHODS

Data were collected from consecutive cases during 2014 until 2018 using clinical records. Multivariate regression analysis was used comparing outcomes per first delivery method.

MAIN OUTCOME MEASURES

Primary outcome was completion of vaginal delivery between all methods of instrumental delivery. Secondary outcome was a composite of immediate perinatal adverse outcomes for instrumental delivery modes and primary full dilation caesarean section.

RESULTS

From 971 deliveries analysed: ventouse delivery was significantly less likely to achieve vaginal delivery compared with Keilland's forceps delivery (odds ratio [OR] 0.42, 95% CI 0.22-0.79). Once confounding factors were adjusted for, adverse outcome rates were less frequent in the Keilland's forceps group than with primary full dilation caesarean section (OR 0.37, 95% CI 0.16-0.81); however, the receiver operating characteristic curve produced from this model demonstrated a low predictive value (AUC 0.64).

CONCLUSIONS

Attempting instrumental delivery in delivery suite theatre, as an alternative to primary emergency full dilation caesarean section, is both reasonable and safe. In this study, ventouse delivery performed poorly in comparison with other modes of instrumental delivery. Further research in the form of randomised controlled trials to identify the optimal mode of second stage delivery is paramount.

TWEETABLE ABSTRACT

Instrumental delivery trials in theatre are safe but use of ventouse was associated with a higher rate of failure.

Disease extent and anti-tubercular treatment response correlates with Mycobacterium tuberculosis-specific CD4 T-cell phenotype regardless of HIV-1 status

Objectives

The development of non‐sputum‐based assays for tuberculosis (TB) diagnosis and treatment monitoring is a key priority. Recent data indicate that whole blood‐based assays to assess the phenotype of Mycobacterium tuberculosis (Mtb)‐specific CD4 T cells hold promise for this purpose and require further investigation in well‐characterised TB cohorts. In this study, we investigated the relationship between the phenotypic signature of Mtb‐specific CD4 responses, TB disease extent and treatment response.

Methods

Using flow cytometry, we measured the expression of phenotypic and functional markers (HLA‐DR, CD27, CD153, KLRG1, IL‐2, MIP‐1β, TNF‐α and IFN‐γ) on Mtb‐specific CD4 T‐cells in whole blood from 161 participants of varying TB and HIV status. TB disease extent was graded as a continuum using the Xpert_ct value, C‐reactive protein, Timika radiographic score and monocyte/lymphocyte ratio.

Results

The phenotypic profile of Mtb‐specific CD4 T cells pre‐anti‐tubercular treatment (ATT) strongly correlated with disease extent, irrespective of HIV status. ATT associated with major changes in the phenotype of Mtb‐specific CD4 T cells, with decreased expression of HLA‐DR and increased CD27 and CD153 expression. Principal component analysis showed an almost complete separation between latent TB infection (LTBI) and active TB (aTB) pre‐ATT groups, whereas the profile of the aTB post‐ATT group overlapped with the LTBI group. However, in patients experiencing treatment failure or relapse, no significant changes were observed in Mtb‐specific CD4 T‐cell phenotype pre‐ and post‐ATT.

Conclusion

Whole blood‐based assays of Mtb‐specific CD4 T‐cell activation and maturation markers can be used as non‐sputum‐based biomarkers of disease extent and treatment monitoring in TB, regardless of HIV‐1 status.

Visualizing the Selectivity and Dynamics of Interferon Signaling In Vivo

Interferons (IFN) are pleiotropic cytokines essential for defense against infection, but the identity and tissue distribution of IFN-responsive cells in vivo are poorly defined. In this study, we generate a mouse strain capable of reporting IFN-signaling activated by all three types of IFNs and investigate the spatio-temporal dynamics and identity of IFN-responding cells following IFN injection and influenza virus infection. Despite ubiquitous expression of IFN receptors, cellular responses to IFNs are highly heterogenous in vivo and are determined by anatomical site, cell type, cellular preference to individual IFNs, and activation status. Unexpectedly, type I and II pneumocytes, the primary target of influenza infection, exhibit striking differences in the strength and temporal dynamics of IFN signaling associated with differential susceptibility to the viral infection. Our findings suggest that time- and cell-type-dependent integration of distinct IFN signals govern the specificity and magnitude of IFN responses in vivo.

Predicting left ventricular contractile function via Gaussian process emulation in aortic-banded rats

Cardiac contraction is the result of integrated cellular, tissue and organ function. Biophysical in silico cardiac models offer a systematic approach for studying these multi-scale interactions. The computational cost of such models is high, due to their multi-parametric and nonlinear nature. This has so far made it difficult to perform model fitting and prevented global sensitivity analysis (GSA) studies. We propose a machine learning approach based on Gaussian process emulation of model simulations using probabilistic surrogate models, which enables model parameter inference via a Bayesian history matching (HM) technique and GSA on whole-organ mechanics. This framework is applied to model healthy and aortic-banded hypertensive rats, a commonly used animal model of heart failure disease. The obtained probabilistic surrogate models accurately predicted the left ventricular pump function (R² = 0.92 for ejection fraction). The HM technique allowed us to fit both the control and diseased virtual bi-ventricular rat heart models to magnetic resonance imaging and literature data, with model outputs from the constrained parameter space falling within 2 SD of the respective experimental values. The GSA identified Troponin C and cross-bridge kinetics as key parameters in determining both systolic and diastolic ventricular function. This article is part of the theme issue 'Uncertainty quantification in cardiac and cardiovascular modelling and simulation'.

Circulating inflammatory mediators as biomarkers of ocular toxoplasmosis in acute and in chronic infection

Toxoplasmosis is highly endemic worldwide. In Brazil, depending on the geographical region and socioeconomic status, 40-70% of individuals become seropositive at some point in their lives. A significant proportion of Toxoplasma gondii-chronically infected individuals who are otherwise immunocompetent develop recurrent ocular lesions. The inflammatory/immune mechanisms involved in development of ocular lesion are still unknown and, despite previous investigation, there are no reliable immune biomarkers to predict/follow disease outcome. To better understand the impact of the immune response on parasite control and immunopathology of ocular toxoplasmosis, and to provide insights on putative biomarkers for disease monitoring, we assessed the production of a large panel of circulating immune mediators in a longitudinal study of patients with postnatally acquired toxoplasmosis stratified by the presence of ocular involvement, both at the early acute stage and 6 months later during chronic infection, correlating them with presence of ocular involvement. We found that T. gondii-infected patients, especially during the acute stage of the disease, display high levels of chemokines, cytokines, and growth factors involved in the activation, proliferation, and migration of inflammatory cells to injured tissues. In particular, major increases were found in the IFN-induced chemokines CXCL9 and CXCL10 in T. gondii-infected patients regardless of disease stage or clinical manifestations. Moreover, a specific subgroup of circulating cytokines and chemokines including GM-CSF, CCL25, CCL11, CXCL12, CXCL13, and CCL2 was identified as potential biomarkers that accurately distinguish different stages of infection and predict the occurrence of ocular toxoplasmosis. In addition to serving as predictors of disease development, these host inflammatory molecules may offer promise as candidate targets for therapeutic intervention.

IL-12 derived from CD8α+ dendritic cells drives the differentiation of innate-like T-bethigh memory-phenotype CD4+ T lymphocytes in steady state

CD4+ T lymphocytes consist of naïve, antigen-specific memory, and memory-phenotype (MP) cell compartments in steady state. We recently showed that MP cells exert innate-like effector function in host defense. However, it remained to be defined whether MP cell population comprises multiple subsets, and if so, what factors determine their selective differentiation under homeostatic conditions. Here we characterize MP lymphocytes as consisting of T-bethigh, T-betlow, and T-bet− subsets, with innate Th1-like effector activity exclusively associated with T-bethigh cells. We further show that steady-state differentiation of T-bethigh MP cells is promoted by IL-12-producing CD8α+ dendritic cells (DC1). Finally, we present evidence arguing that this tonic IL-12 production requires TLR-MyD88 signaling triggered independently of foreign agonists and is further enhanced by CD40-CD40L interactions with self-dependent MP CD4+ T lymphocytes. Thus, optimal differentiation of T-bethigh MP lymphocytes in steady state requires IL-12 tonically produced by DC1 in an MyD88 and CD40 signaling-dependent fashion.

This work was in part supported by the Intramural Research Program of the NIAID and NCI, NIH.

The transcription factor BACH1 promotes tissue damage and host susceptibility in Mycobacterium tuberculosis infection by reducing expression of Gpx4, a major negative regulator of ferroptosis

Ferroptosis is a type of regulated necrotic cell death induced by the acumulation of free iron and lipid peroxides. We have previously described a role for ferroptosis in Mtb-induced macrophage necrosis based on its biochemical requirements and its blockade both in vitro and in vivo by a lipid peroxidation inhibitor (fer-1). To help validate these findings and further delineate the mechanism involved we have analyzed Mtb-induced cellular necrosis and host resistance in mice deficient in or overexpressing glutathione peroxidase (Gpx4), an essential regulator of ferroptosis. To do so we generated conditional-knockout mice for Gpx4 by using creERT2, CD45cre and LysMcre systems targeting different cell compartments. After aerosol low dose Mtb infection these conditional-knockout mice showed both increased lung necrosis and elevated pulmonary and splenic bacterial burdens. In the opposite direction, Gpx4-overexpressing mice infected at high dose with Mtb were found to display decreased bacterial burdens as well as reduced pulmonary necrosis. Genetic deletion of BACH1, a transcription factor known to repress antioxidant genes including Gpx4, increased the levels of intracellular glutathione as well as enhanced expression of Gpx4 during Mtb infection in vitro and in vivo. Moreover, Bach1−/− mice infected at high dose with Mtb displayed a significant reduction in bacterial loads and lung necrosis along with lowered levels of lipid peroxides as well as enhanced survival. Together, these findings provide genetic evidence further delineating the role of ferroptosis as a mechanism of host cell death and tissue necrosis in Mtb infection and implicate both Gpx4 and Bach1 as potential targets for host-direct therapy of tuberculosis.

The Magnitude of IFN-γ Responses Is Fine-Tuned by DNA Architecture and the Non-coding Transcript of Ifng-as1

Interferon gamma (IFN-γ), critical for host defense and tumor surveillance, requires tight control of its expression. Multiple cis-regulatory elements exist around Ifng along with a non-coding transcript, Ifng-as1 (also termed NeST). Here, we describe two genetic models generated to dissect the molecular functions of this locus and its RNA product. DNA deletion within the Ifng-as1 locus disrupted chromatin organization of the extended Ifng locus, impaired Ifng response, and compromised host defense. Insertion of a polyA signal ablated the Ifng-as1 full-length transcript and impaired host defense, while allowing proper chromatin structure. Transient knockdown of Ifng-as1 also reduced IFN-γ production. In humans, discordant expression of IFNG and IFNG-AS1 was evident in memory T cells, with high expression of this long non-coding RNA (lncRNA) and low expression of the cytokine. These results establish Ifng-as1 as an important regulator of Ifng expression, as a DNA element and transcribed RNA, involved in dynamic and cell state-specific responses to infection.

Student perceptions of two simulated learning environments in paediatric audiology

Objective: To determine audiology student perceptions of two simulated learning environments (SLE) in paediatric audiology.Design: A one-shot case study design.Study sample: Fifteen audiology students who completed questionnaires after participating in two SLEs, one simulating auditory brainstem response (ABR) assessments of neonates in a hospital ward and one simulating visually reinforced orientation audiometry (VROA) assessments of young children in an audiology clinic.Results: The students responded positively to 11/11 areas of audiometric testing and client interaction in both SLEs, to 7/7 aspects of their interactions with the mannequins in both SLEs, and to 8/8 aspects of their interactions with fellow students playing the role of parent in the ABR SLE and 7/8 of these aspects in the VROA SLE. The students reported low levels of anxiety towards both SLEs but rated the ABR SLE more highly than the VROA SLE in areas of preparedness, effectiveness, realism, pre-SLE training, reinforcement of lecture content, and overall usefulness.Conclusions: The participating students responded positively to almost all aspects of both SLEs. Further research is warranted using research designs capable of determining if these SLEs directly improve student abilities as they transition from academic settings to clinical placements in paediatric audiology.

Transcriptional profiling unveils type I and II interferon networks in blood and tissues across diseases

Understanding how immune challenges elicit different responses is critical for diagnosing and deciphering immune regulation. Using a modular strategy to interpret the complex transcriptional host response in mouse models of infection and inflammation, we show a breadth of immune responses in the lung. Lung immune signatures are dominated by either IFN-γ and IFN-inducible, IL-17-induced neutrophil- or allergy-associated gene expression. Type I IFN and IFN-γ-inducible, but not IL-17- or allergy-associated signatures, are preserved in the blood. While IL-17-associated genes identified in lung are detected in blood, the allergy signature is only detectable in blood CD4+ effector cells. Type I IFN-inducible genes are abrogated in the absence of IFN-γ signaling and decrease in the absence of IFNAR signaling, both independently contributing to the regulation of granulocyte responses and pathology during Toxoplasma gondii infection. Our framework provides an ideal tool for comparative analyses of transcriptional signatures contributing to protection or pathogenesis in disease.

Molecular degree of perturbation of plasma inflammatory markers associated with tuberculosis reveals distinct disease profiles between Indian and Chinese populations

Tuberculosis (TB) is a chronic inflammatory disease caused by Mycobacterium tuberculosis infection which causes tremendous morbidity and mortality worldwide. Clinical presentation of TB patients is very diverse and disease heterogeneity is associated with changes in biomarker signatures. Here, we compared at the molecular level the extent of individual inflammatory perturbation of plasma protein and lipid mediators associated with TB in patients in China versus India. We performed a cross-sectional study analyzing the overall degree of inflammatory perturbation in treatment-naïve pulmonary TB patients and uninfected individuals from India (TB: n = 97, healthy: n = 20) and China (TB: n = 100, healthy: n = 11). We employed the molecular degree of perturbation (MDP) adapted to plasma biomarkers to examine the overall changes in inflammation between these countries. M. tuberculosis infection caused a significant degree of molecular perturbation in patients from both countries, with higher perturbation detected in India. Interestingly, there were differences in biomarker perturbation patterns and the overall degree of inflammation. Patients with severe TB exhibited increased MDP values and Indian patients with this condition exhibited even higher degree of perturbation compared to Chinese patients. Network analyses identified IFN-α, IFN-β, IL-1RI and TNF-α as combined biomarkers that account for the overall molecular perturbation in the entire study population. Our results delineate the magnitude of the systemic inflammatory perturbation in pulmonary TB and reveal qualitative changes in inflammatory profiles between two countries with high disease prevalence.

Host Resistance to pulmonary Mycobacterium tuberculosis infection requires CD153 expression

Mycobacterium tuberculosis infection (Mtb) is the leading cause of death due to a single infectious agent and is among the top ten causes of all human deaths worldwide. CD4 T cells are essential for resistance to Mtb infection, and for decades it has been thought that IFNγ production is the primary mechanism of CD4 T-cell-mediated protection. However, IFNγ responses do not correlate with host protection, and several reports demonstrate that additional anti-tuberculosis CD4 T-cell effector functions remain unaccounted for. Here we show that the tumour-necrosis factor (TNF) superfamily molecule CD153 (encoded by the gene Tnfsf8) is required for control of pulmonary Mtb infection by CD4 T cells. CD153-deficient mice develop high pulmonary bacterial loads and succumb early to Mtb infection. Reconstitution of T-cell-deficient hosts with Tnfsf8−/− CD4 T cells, similar to Ifng−/− CD4 T cells, fails to rescue mice from early mortality. In Mtb-infected non-human primates, Mtb-specific CD153-expressing CD4 T cells inversely correlates with bacterial loads in granulomas. In Mtb-infected humans, CD153 defines a subset of highly polyfunctional Mtb-specific CD4 T cells that are much more abundant in individuals with latent Mtb infection compared to those with active tuberculosis. Thus, CD153 is a major immune mediator of host protection against pulmonary Mtb infection and CD4 T cells are one important source of this molecule.

T-bet expression is fine-tuned for balancing IFN-γ-producing Th1 and Tfh cell differentiation and IgG2a(c) production

T follicular helper (Tfh) cells and cytokine IFN-γ are involved in Ig class switching in B cells to produce IgG2a(c). Tfh cells mainly produce IL-21 as their signature cytokine, and several studies have also shown that some Tfh cells are capable of expressing Th1 signature cytokine IFN-γ without expressing the Th1 master transcription factor T-bet. In Toxoplasma gondii peptide AS15/Complete Freund’s Adjuvant (CFA)-induced immune response, we found antigen AS15-specific IgG2a(c) were abolished in CD4-Cre-mediated T-bet-deficient mice. By using T-bet-fate-mapping mouse strains, we reported that transient expression of T-bet epigenetically imprints the Ifng locus for cytokine production in a subset of Tfh cells; In germinal centers, multi-color tissue imaging revealed that the ex-T-bet Tfh cells express IFN-γ in situ; IFN-γ-expressing Tfh cells are absent in T-bet-deficient mice. More interestingly, we noticed that IFN-γ-expressing Tfh cells were fully present in mice with T-bet deletion at late stages of T cell differentiation, and antigen AS15-specific IgG2a(c) were even further up-regulated in such “T-bet late knockout” mice. Taken together, our findings demonstrate that IFN-γ expressed by T cells plays a dominant role in antibody IgG2a(c) production; T-bet expression is fine-tuned as spatiotemporal manner for balancing Th1 and Tfh cell differentiation in vivo and regulating the strength of antibody production.