Galleria mellonella-intracellular bacteria pathogen infection models: the ins and outs.

Galleria mellonella (greater wax moth) larvae are used widely as surrogate infectious disease models, due to ease of use and the presence of an innate immune system functionally similar to that of vertebrates. Here, we review G. mellonella-human intracellular bacteria pathogen infection models from the genera Burkholderia, Coxiella, Francisella, Listeria, and Mycobacterium. For all genera, G. mellonella use has increased understanding of host-bacterial interactive biology, particularly through studies comparing the virulence of closely related species and/or wild-type versus mutant pairs. In many cases, virulence in G. mellonella mirrors that found in mammalian infection models, although it is unclear whether the pathogenic mechanisms are the same. The use of G. mellonella larvae has speeded up in vivo efficacy and toxicity testing of novel antimicrobials to treat infections caused by intracellular bacteria: an area that will expand since the FDA no longer requires animal testing for licensure. Further use of G. mellonella-intracellular bacteria infection models will be driven by advances in G. mellonella genetics, imaging, metabolomics, proteomics, and transcriptomic methodologies, alongside the development and accessibility of reagents to quantify immune markers, all of which will be underpinned by a fully annotated genome.

Comparative transcriptomic analysis of whole blood mycobacterial growth assays and tuberculosis patients' blood RNA profiles.

In vitro whole blood infection models are used for elucidating the immune response to Mycobacterium tuberculosis (Mtb). They exhibit commonalities but also differences, to the in vivo blood transcriptional response during natural human Mtb disease. Here, we present a description of concordant and discordant components of the immune response in blood, quantified through transcriptional profiling in an in vitro whole blood infection model compared to whole blood from patients with tuberculosis disease. We identified concordantly and discordantly expressed gene modules and performed in silico cell deconvolution. A high degree of concordance of gene expression between both adult and paediatric in vivo-in vitro tuberculosis infection was identified. Concordance in paediatric in vivo vs in vitro comparison is largely characterised by immune suppression, while in adults the comparison is marked by concordant immune activation, particularly that of inflammation, chemokine, and interferon signalling. Discordance between in vitro and in vivo increases over time and is driven by T-cell regulation and monocyte-related gene expression, likely due to apoptotic depletion of monocytes and increasing relative fraction of longer-lived cell types, such as T and B cells. Our approach facilitates a more informed use of the whole blood in vitro model, while also accounting for its limitations.

Galleria mellonella as an infection model for the virulent Mycobacterium tuberculosis H37Rv.

Tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), is a leading cause of infectious disease mortality. Animal infection models have contributed substantially to our understanding of TB, yet their biological and non-biological limitations are a research bottleneck. There is a need for more ethically acceptable, economical, and reproducible TB infection models capable of mimicking key aspects of disease. Here, we demonstrate and present a basic description of how Galleria mellonella (the greater wax moth, Gm) larvae can be used as a low cost, rapid, and ethically more acceptable model for TB research. This is the first study to infect Gm with the fully virulent MTB H37Rv, the most widely used strain in research. Infection of Gm with MTB resulted in a symptomatic lethal infection, the virulence of which differed from both attenuated Mycobacterium bovis BCG and auxotrophic MTB strains. The Gm-MTB model can also be used for anti-TB drug screening, although CFU enumeration from Gm is necessary for confirmation of mycobacterial load reducing activity of the tested compound. Furthermore, comparative virulence of MTB isogenic mutants can be determined in Gm. However, comparison of mutant phenotypes in Gm against conventional models must consider the limitations of innate immunity. Our findings indicate that Gm will be a practical, valuable, and advantageous additional model to be used alongside existing models to advance tuberculosis research.

Innate Immune Responses of Galleria mellonella to Mycobacterium bovis BCG Challenge Identified Using Proteomic and Molecular Approaches.

The larvae of the insect Galleria mellonella, have recently been established as a non-mammalian infection model for the Mycobacterium tuberculosis complex (MTBC). To gain further insight into the potential of this model, we applied proteomic (label-free quantification) and transcriptomic (gene expression) approaches to characterise the innate immune response of G. mellonella to infection with Mycobacterium bovis BCG lux over a 168 h time course. Proteomic analysis of the haemolymph from infected larvae revealed distinct changes in the proteome at all time points (4, 48, 168 h). Reverse transcriptase quantitative PCR confirmed induction of five genes (gloverin, cecropin, IMPI, hemolin, and Hdd11), which encoded proteins found to be differentially abundant from the proteomic analysis. However, the trend between gene expression and protein abundance were largely inconsistent (20%). Overall, the data are in agreement with previous phenotypic observations such as haemocyte internalization of mycobacterial bacilli (hemolin/ß-actin), formation of granuloma-like structures (Hdd11), and melanization (phenoloxidase activating enzyme 3 and serpins). Furthermore, similarities in immune expression in G. mellonella, mouse, zebrafish and in vitro cell-line models of tuberculosis infection were also identified for the mechanism of phagocytosis (ß-actin). Cecropins (antimicrobial peptides), which share the same α-helical motif as a highly potent peptide expressed in humans (h-CAP-18), were induced in G. mellonella in response to infection, giving insight into a potential starting point for novel antimycobacterial agents. We believe that these novel insights into the innate immune response further contribute to the validation of this cost-effective and ethically acceptable insect model to study members of the MTBC.

A novel biosafety level 2 compliant tuberculosis infection model using a ΔleuDΔpanCD double auxotroph of Mycobacterium tuberculosis H37Rv and Galleria mellonella.

Mammalian infection models have contributed significantly to our understanding of the host-mycobacterial interaction, revealing potential mechanisms and targets for novel antimycobacterial therapeutics. However, the use of conventional mammalian models such as mice, are typically expensive, high maintenance, require specialized animal housing, and are ethically regulated. Furthermore, research using Mycobacterium tuberculosis (MTB), is inherently difficult as work needs to be carried out at biosafety level 3 (BSL3). The insect larvae of Galleria mellonella (greater wax moth), have become increasingly popular as an infection model, and we previously demonstrated its potential as a mycobacterial infection model using Mycobacterium bovis BCG. Here we present a novel BSL2 complaint MTB infection model using G. mellonella in combination with a bioluminescent ΔleuDΔpanCD double auxotrophic mutant of MTB H37Rv (SAMTB lux) which offers safety and practical advantages over working with wild type MTB. Our results show a SAMTB lux dose dependent survival of G. mellonella larvae and demonstrate proliferation and persistence of SAMTB lux bioluminescence over a 1 week infection time course. Histopathological analysis of G. mellonella, highlight the formation of early granuloma-like structures which matured over time. We additionally demonstrate the drug efficacy of first (isoniazid, rifampicin, and ethambutol) and second line (moxifloxacin) antimycobacterial drugs. Our findings demonstrate the broad potential of this insect model to study MTB infection under BSL2 conditions. We anticipate that the successful adaptation and implementation of this model will remove the inherent limitations of MTB research at BSL3 and increase tuberculosis research output.

Ultra-Short Antimicrobial Peptoids Show Propensity for Membrane Activity Against Multi-Drug Resistant Mycobacterium tuberculosis.

Tuberculosis (TB) results in both morbidity and mortality on a global scale. With drug resistance on the increase, there is an urgent need to develop novel anti-mycobacterials. Thus, we assessed the anti-mycobacterial potency of three novel synthetic peptoids against drug-susceptible and multi-drug resistant (MDR) Mycobacterium tuberculosis in vitro using Minimum Inhibitory Concentration, killing efficacy and intracellular growth inhibition assays, and in vivo against mycobacteria infected BALB/c mice. In addition, we verified cell selectivity using mammalian cells to assess peptoid toxicity. The mechanism of action was determined using flow cytometric analysis, and microfluidic live-cell imaging with time-lapse microscopy and uptake of propidium iodide. Peptoid BM 2 demonstrated anti-mycobacterial activity against both drug sensitive and MDR M. tuberculosis together with an acceptable toxicity profile that showed selectivity between bacterial and mammalian membranes. The peptoid was able to efficiently kill mycobacteria both in vitro and intracellularly in murine RAW 264.7 macrophages, and significantly reduced bacterial load in the lungs of infected mice. Flow cytometric and time lapse fluorescence microscopy indicate mycobacterial membrane damage as the likely mechanism of action. These data demonstrate that peptoids are a novel class of antimicrobial which warrant further investigation and development as therapeutics against TB.

Galleria mellonella: An Infection Model for Screening Compounds Against the Mycobacterium tuberculosis Complex.

Drug screening models have a vital role in the development of novel antimycobacterial agents which are urgently needed to tackle drug-resistant tuberculosis (TB). We recently established the larvae of the insect Galleria mellonella (greater wax moth) as a novel infection model for the Mycobacterium tuberculosis complex. Here we demonstrate its use as a rapid and reproducible screen to evaluate antimycobacterial drug efficacy using larvae infected with bioluminescent Mycobacterium bovis BCG lux. Treatment improved larval survival outcome and, with the exception of pyrazinamide, was associated with a significant reduction in in vivo mycobacterial bioluminescence over a 96 h period compared to the untreated controls. Isoniazid and rifampicin displayed the greatest in vivo efficacy and survival outcome. Thus G. mellonella, infected with bioluminescent mycobacteria, can rapidly determine in vivo drug efficacy, and has the potential to significantly reduce and/or replace the number of animals used in TB research.

Use of the Invertebrate Galleria mellonella as an Infection Model to Study the Mycobacterium tuberculosis Complex.

Tuberculosis is the leading global cause of infectious disease mortality and roughly a quarter of the world's population is believed to be infected with Mycobacterium tuberculosis. Despite decades of research, many of the mechanisms behind the success of M. tuberculosis as a pathogenic organism remain to be investigated, and the development of safer, more effective antimycobacterial drugs are urgently needed to tackle the rise and spread of drug resistant tuberculosis. However, the progression of tuberculosis research is bottlenecked by traditional mammalian infection models that are expensive, time consuming, and ethically challenging. Previously we established the larvae of the insect Galleria mellonella (greater wax moth) as a novel, reproducible, low cost, high-throughput and ethically acceptable infection model for members of the M. tuberculosis complex. Here we describe the maintenance, preparation, and infection of G. mellonella with bioluminescent Mycobacterium bovis BCG lux. Using this infection model, mycobacterial dose dependent virulence can be observed, and a rapid readout of in vivo mycobacterial burden using bioluminescence measurements is easily achievable and reproducible. Although limitations exist, such as the lack of a fully annotated genome for transcriptomic analysis, ontological analysis against genetically similar insects can be carried out. As a low cost, rapid, and ethically acceptable model for tuberculosis, G. mellonella can be used as a pre-screen to determine drug efficacy and toxicity, and to determine comparative mycobacterial virulence prior to the use of conventional mammalian models. The use of the G. mellonella-mycobacteria model will lead to a reduction in the substantial number of animals currently used in tuberculosis research.

Galleria mellonella - a novel infection model for the Mycobacterium tuberculosis complex.

Animal models have long been used in tuberculosis research to understand disease pathogenesis and to evaluate novel vaccine candidates and anti-mycobacterial drugs. However, all have limitations and there is no single animal model which mimics all the aspects of mycobacterial pathogenesis seen in humans. Importantly mice, the most commonly used model, do not normally form granulomas, the hallmark of tuberculosis infection. Thus there is an urgent need for the development of new alternative in vivo models. The insect larvae, Galleria mellonella has been increasingly used as a successful, simple, widely available and cost-effective model to study microbial infections. Here we report for the first time that G. mellonella can be used as an infection model for members of the Mycobacterium tuberculosis complex. We demonstrate a dose-response for G. mellonella survival infected with different inocula of bioluminescent Mycobacterium bovis BCG lux, and demonstrate suppression of mycobacterial luminesence over 14 days. Histopathology staining and transmission electron microscopy of infected G. mellonella phagocytic haemocytes show internalization and aggregation of M. bovis BCG lux in granuloma-like structures, and increasing accumulation of lipid bodies within M. bovis BCG lux over time, characteristic of latent tuberculosis infection. Our results demonstrate that G. mellonella can act as a surrogate host to study the pathogenesis of mycobacterial infection and shed light on host-mycobacteria interactions, including latent tuberculosis infection.

Mycobacterium tuberculosis Exploits a Molecular Off Switch of the Immune System for Intracellular Survival.

Mycobacterium tuberculosis (M. tuberculosis) survives and multiplies inside human macrophages by subversion of immune mechanisms. Although these immune evasion strategies are well characterised functionally, the underlying molecular mechanisms are poorly understood. Here we show that during infection of human whole blood with M. tuberculosis, host gene transcriptional suppression, rather than activation, is the predominant response. Spatial, temporal and functional characterisation of repressed genes revealed their involvement in pathogen sensing and phagocytosis, degradation within the phagolysosome and antigen processing and presentation. To identify mechanisms underlying suppression of multiple immune genes we undertook epigenetic analyses. We identified significantly differentially expressed microRNAs with known targets in suppressed genes. In addition, after searching regions upstream of the start of transcription of suppressed genes for common sequence motifs, we discovered novel enriched composite sequence patterns, which corresponded to Alu repeat elements, transposable elements known to have wide ranging influences on gene expression. Our findings suggest that to survive within infected cells, mycobacteria exploit a complex immune "molecular off switch" controlled by both microRNAs and Alu regulatory elements.

Childhood tuberculosis is associated with decreased abundance of T cell gene transcripts and impaired T cell function.

The WHO estimates around a million children contract tuberculosis (TB) annually with over 80 000 deaths from dissemination of infection outside of the lungs. The insidious onset and association with skin test anergy suggests failure of the immune system to both recognise and respond to infection. To understand the immune mechanisms, we studied genome-wide whole blood RNA expression in children with TB meningitis (TBM). Findings were validated in a second cohort of children with TBM and pulmonary TB (PTB), and functional T-cell responses studied in a third cohort of children with TBM, other extrapulmonary TB (EPTB) and PTB. The predominant RNA transcriptional response in children with TBM was decreased abundance of multiple genes, with 140/204 (68%) of all differentially regulated genes showing reduced abundance compared to healthy controls. Findings were validated in a second cohort with concordance of the direction of differential expression in both TBM (r2 = 0.78 p = 2x10-16) and PTB patients (r2 = 0.71 p = 2x10-16) when compared to a second group of healthy controls. Although the direction of expression of these significant genes was similar in the PTB patients, the magnitude of differential transcript abundance was less in PTB than in TBM. The majority of genes were involved in activation of leucocytes (p = 2.67E-11) and T-cell receptor signalling (p = 6.56E-07). Less abundant gene expression in immune cells was associated with a functional defect in T-cell proliferation that recovered after full TB treatment (p<0.0003). Multiple genes involved in T-cell activation show decreased abundance in children with acute TB, who also have impaired functional T-cell responses. Our data suggest that childhood TB is associated with an acquired immune defect, potentially resulting in failure to contain the pathogen. Elucidation of the mechanism causing the immune paresis may identify new treatment and prevention strategies.

Innate activation of human primary epithelial cells broadens the host response to Mycobacterium tuberculosis in the airways.

Early events in the human airways determining whether exposure to Mycobacterium tuberculosis (Mtb) results in acquisition of infection are poorly understood. Epithelial cells are the dominant cell type in the lungs, but little is known about their role in tuberculosis. We hypothesised that human primary airway epithelial cells are part of the first line of defense against Mtb-infection and contribute to the protective host response in the human respiratory tract. We modelled these early airway-interactions with human primary bronchial epithelial cells (PBECs) and alveolar macrophages. By combining in vitro infection and transwell co-culture models with a global transcriptomic approach, we identified PBECs to be inert to direct Mtb-infection, yet to be potent responders within an Mtb-activated immune network, mediated by IL1ß and type I interferon (IFN). Activation of PBECs by Mtb-infected alveolar macrophages and monocytes increased expression of known and novel antimycobacterial peptides, defensins and S100-family members and epithelial-myeloid interactions further shaped the immunological environment during Mtb-infection by promoting neutrophil influx. This is the first in depth analysis of the primary epithelial response to infection and offers new insights into their emerging role in tuberculosis through complementing and amplifying responses to Mtb.

Disruption of drug-resistant biofilms using de novo designed short α-helical antimicrobial peptides with idealized facial amphiphilicity.

The escalating threat of antimicrobial resistance has increased pressure to develop novel therapeutic strategies to tackle drug-resistant infections. Antimicrobial peptides have emerged as a promising class of therapeutics for various systemic and topical clinical applications. In this study, the de novo design of α-helical peptides with idealized facial amphiphilicities, based on an understanding of the pertinent features of protein secondary structures, is presented. Synthetic amphiphiles composed of the backbone sequence (X1Y1Y2X2)n, where X1 and X2 are hydrophobic residues (Leu or Ile or Trp), Y1 and Y2 are cationic residues (Lys), and n is the number repeat units (2 or 2.5 or 3), demonstrated potent broad-spectrum antimicrobial activities against clinical isolates of drug-susceptible and multi-drug resistant bacteria. Live-cell imaging revealed that the most selective peptide, (LKKL)3, promoted rapid permeabilization of bacterial membranes. Importantly, (LKKL)3 not only suppressed biofilm growth, but effectively disrupted mature biofilms after only 2h of treatment. The peptides (LKKL)3 and (WKKW)3 suppressed the production of LPS-induced pro-inflammatory mediators to levels of unstimulated controls at low micromolar concentrations. Thus, the rational design strategies proposed herein can be implemented to develop potent, selective and multifunctional α-helical peptides to eradicate drug-resistant biofilm-associated infections. STATEMENT OF SIGNIFICANCE: Antimicrobial peptides (AMPs) are increasingly explored as therapeutics for drug-resistant and biofilm-related infections to help expand the size and quality of the current antibiotic pipeline in the face of mounting antimicrobial resistance. Here, synthetic peptides rationally designed based upon principles governing the folding of natural α-helical AMPs, comprising the backbone sequence (X1Y1Y2X2)n, and which assemble into α-helical structures with idealized facial amphiphilicity, is presented. These multifunctional peptide amphiphiles demonstrate high bacterial selectivity, promote the disruption of pre-formed drug-resistant biofilms, and effectively neutralize endotoxins at low micromolar concentrations. Overall, the design strategies presented here could provide a useful tool for developing therapeutic peptides with broad-ranging clinical applications from the treatment and prevention of drug-resistant biofilms to the neutralization of bacterial endotoxins.

Unnatural amino acid analogues of membrane-active helical peptides with anti-mycobacterial activity and improved stability.

OBJECTIVES: The emergence of MDR-TB, coupled with shrinking antibiotic pipelines, has increased demands for new antimicrobials with novel mechanisms of action. Antimicrobial peptides have increasingly been explored as promising alternatives to antibiotics, but their inherent poor in vivo stability remains an impediment to their clinical utility. We therefore systematically evaluated unnatural amino acid-modified peptides to design analogues with enhanced anti-mycobacterial activities. METHODS: Anti-mycobacterial activities were evaluated in vitro and intracellularly against drug-susceptible and MDR isolates of Mycobacterium tuberculosis using MIC, killing efficacy and intracellular growth inhibition studies. Toxicity profiles were assessed against mammalian cells to verify cell selectivity. Anti-mycobacterial mechanisms were investigated using microfluidic live-cell imaging with time-lapse fluorescence microscopy and confocal laser-scanning microscopy. RESULTS: Unnatural amino acid incorporation was well tolerated without an appreciable effect on toxicity profiles and secondary conformations of the synthetic peptides. The modified peptides also withstood proteolytic digestion by trypsin. The all d-amino acid peptide, i(llkk)2i (II-D), displayed superior activity against all six mycobacterial strains tested, with a 4-fold increase in selectivity index as compared with the unmodified l-amino acid peptide in broth. II-D effectively reduced the intracellular bacterial burden of both drug-susceptible and MDR clinical isolates of M. tuberculosis after 4 days of treatment. Live-cell imaging studies demonstrated that II-D permeabilizes the mycobacterial membrane, while confocal microscopy revealed that II-D not only permeates the cell membrane, but also accumulates within the cytoplasm. CONCLUSIONS: Unnatural amino acid modifications not only decreased the susceptibility of peptides to proteases, but also enhanced mycobacterial selectivity.

Understanding immune protection against tuberculosis using RNA expression profiling.

A major limitation in the development and testing of new tuberculosis (TB) vaccines is the current inadequate understanding of the nature of the immune response required for protection against either infection with Mycobacterium tuberculosis (MTB) or progression to disease. Genome wide RNA expression analysis has provided a new tool with which to study the inflammatory and immunological response to mycobacteria. To explore how currently available transcriptomic data might be used to understand the basis of protective immunity to MTB, we analysed and reviewed published RNA expression studies to (1) identify a "susceptible" immune response in patients with acquired defects in the interferon gamma pathway; (2) identify the "failing" transcriptomic response in patients with TB as compared with latent TB infection (LTBI); and (3) identify elements of the "protective" response in healthy latently infected and healthy uninfected individuals.

Functional drug screening reveals anticonvulsants as enhancers of mTOR-independent autophagic killing of Mycobacterium tuberculosis through inositol depletion.

Mycobacterium tuberculosis (MTB) remains a major challenge to global health made worse by the spread of multidrug resistance. We therefore examined whether stimulating intracellular killing of mycobacteria through pharmacological enhancement of macroautophagy might provide a novel therapeutic strategy. Despite the resistance of MTB to killing by basal autophagy, cell-based screening of FDA-approved drugs revealed two anticonvulsants, carbamazepine and valproic acid, that were able to stimulate autophagic killing of intracellular M. tuberculosis within primary human macrophages at concentrations achievable in humans. Using a zebrafish model, we show that carbamazepine can stimulate autophagy in vivo and enhance clearance of M. marinum, while in mice infected with a highly virulent multidrug-resistant MTB strain, carbamazepine treatment reduced bacterial burden, improved lung pathology and stimulated adaptive immunity. We show that carbamazepine induces antimicrobial autophagy through a novel, evolutionarily conserved, mTOR-independent pathway controlled by cellular depletion of myo-inositol. While strain-specific differences in susceptibility to in vivo carbamazepine treatment may exist, autophagy enhancement by repurposed drugs provides an easily implementable potential therapy for the treatment of multidrug-resistant mycobacterial infection.

Anti-mycobacterial activities of synthetic cationic α-helical peptides and their synergism with rifampicin.

The rapid emergence of multi-drug resistant tuberculosis (TB) and the lack of effective therapies have prompted the development of compounds with novel mechanisms of action to tackle this growing public health concern. In this study, a series of synthetic cationic α-helical antimicrobial peptides (AMPs) modified with different hydrophobic amino acids was investigated for their anti-mycobacterial activity, both alone and in synergistic combinations with the frontline anti-tuberculosis drug rifampicin. The addition of thiol groups by incorporating cysteine residues in the AMPs did not improve anti-mycobacterial activity against drug-susceptible and drug-resistant Mycobacterium tuberculosis, while the enhancement of peptide hydrophobicity by adding methionine residues increased the efficacy of the primary peptide against all strains tested, including clinically isolated multidrug-resistant mycobacteria. The peptide with the optimal composition M(LLKK)2M was bactericidal, and eradicated mycobacteria via a membrane-lytic mechanism as demonstrated by confocal microscopic studies. Mycobacteria did not develop resistance after multiple exposures to sub-lethal doses of the peptide. In addition, the peptide displayed synergism with rifampicin against both Mycobacterium smegmatis and Mycobacterium bovis BCG and additivity against M. tuberculosis. Moreover, such combination therapy is effective in delaying the emergence of rifampicin resistance. The ability to potentiate anti-TB drug activity, kill drug-resistant bacteria and prevent drug resistance highlights the potential utility of the peptide in combating multidrug-resistant TB.

Azithromycin blocks autophagy and may predispose cystic fibrosis patients to mycobacterial infection.

Azithromycin is a potent macrolide antibiotic with poorly understood antiinflammatory properties. Long-term use of azithromycin in patients with chronic inflammatory lung diseases, such as cystic fibrosis (CF), results in improved outcomes. Paradoxically, a recent study reported that azithromycin use in patients with CF is associated with increased infection with nontuberculous mycobacteria (NTM). Here, we confirm that long-term azithromycin use by adults with CF is associated with the development of infection with NTM, particularly the multi-drug-resistant species Mycobacterium abscessus, and identify an underlying mechanism. We found that in primary human macrophages, concentrations of azithromycin achieved during therapeutic dosing blocked autophagosome clearance by preventing lysosomal acidification, thereby impairing autophagic and phagosomal degradation. As a consequence, azithromycin treatment inhibited intracellular killing of mycobacteria within macrophages and resulted in chronic infection with NTM in mice. Our findings emphasize the essential role for autophagy in the host response to infection with NTM, reveal why chronic use of azithromycin may predispose to mycobacterial disease, and highlight the dangers of inadvertent pharmacological blockade of autophagy in patients at risk of infection with drug-resistant pathogens.

Genetic determination of the effect of post-translational modification on the innate immune response to the 19 kDa lipoprotein of Mycobacterium tuberculosis.

BACKGROUND: The 19 kDa lipoprotein of Mycobacterium tuberculosis (MTB) is an important target of the innate immune response. To investigate the effect of post-translation modification of this protein on innate recognition in the context of the whole bacillus, we derived a recombinant M. tuberculosis H37Rv that lacked the 19 kDa gene (Delta19) and complemented this strain by reintroduction of the 19 kDa gene into the chromosome as a single copy to produce Delta19::19. We also reintroduced the 19 kDa gene in two modified forms that lacked motifs for acylation (Delta19::19NA) and O-glycosylation (Delta19::19NOG). RESULTS: Both acylation and O-glycosylation were necessary for the protein to remain within the cell. IL-1 Beta secretion from human monocytes was significantly reduced by deletion of the 19 kDa gene (p < 0.02). Complementation by the wild type, but not the mutagenised gene reversed this phenotype. The effect of deletion and complementation on IL-12p40 and TNF secretion was less marked with no statistically significant differences between strains. Although deletion of the 19 kDa reduced apoptosis, an effect that could also only be reversed by complementation with the wild type gene, the results were variable between donors and did not achieve statistical significance. CONCLUSION: These results confirm in the context of the whole bacillus an important role for post-translational modification of the 19 kDa on both the cellular location and immune response to this protein.

1alpha,25-dihydroxyvitamin D3 inhibits matrix metalloproteinases induced by Mycobacterium tuberculosis infection.

Matrix metalloproteinases (MMP) can degrade all components of pulmonary extracellular matrix. Mycobacterium tuberculosis induces production of a number of these enzymes by human macrophages, and these are implicated in the pathogenesis of pulmonary cavitation in tuberculosis. The active metabolite of vitamin D, 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)], has previously been reported to inhibit secretion of MMP-9 in human monocytes (MN), but its influence on the secretion and gene expression of MMP and tissue inhibitors of MMP (TIMP) in M. tuberculosis-infected cells has not previously been investigated. We therefore determined the effects of 1alpha,25(OH)(2)D(3) on expression, secretion and activity of a number of MMP and TIMP in M. tuberculosis-infected human leucocytes; we also investigated the effect of 1alpha,25(OH)(2)D(3) on the secretion of interleukin-10 (IL-10) and prostaglandin E(2) (PGE(2)), both transcriptional regulators of MMP expression. We found that M. tuberculosis induced expression of MMP-1, MMP-7 and MMP-10 in MN and MMP-1 and MMP-10 in peripheral blood mononuclear cells (PBMC). 1alpha,25(OH)(2)D(3) significantly attenuated M. tuberculosis-induced increases in expression of MMP-7 and MMP-10, and suppressed secretion of MMP-7 by M. tuberculosis-infected PBMC. MMP-9 gene expression, secretion and activity were significantly inhibited by 1alpha,25(OH)(2)D(3) irrespective of infection. In contrast, the effects of 1alpha,25(OH)(2)D(3) on the expression of TIMP-1, TIMP-2 and TIMP-3 and secretion of TIMP-1 and TIMP-2 were small and variable. 1alpha,25(OH)(2)D(3) also induced secretion of IL-10 and PGE(2) from M. tuberculosis-infected PBMC. These findings represent a novel immunomodulatory role for 1alpha,25(OH)(2)D(3) in M. tuberculosis infection.