Mycobacterium tuberculosis escapes from the phagosomes of infected human osteoclasts reprograms osteoclast development via dysregulation of cytokines and chemokines

Metabolic switching and cell wall remodelling of Mycobacterium tuberculosis during bone tuberculosis

OBJECTIVES

Bone tuberculosis (TB) is the third most common types of extrapulmonary tuberculosis. It is critical to understand mycobacterial adaptive strategies within bone lesions to identify mycobacterial factors that may have role in disease pathogenesis.

METHODS

Whole genome microarray was used to characterize the in-vivo transcriptome of Mycobacterium tuberculosis (M.tb) within bone TB specimens. Mycobacterial virulent proteins were identified by bioinformatic software. An in vitro osteoblast cell line model was used to study the role of these proteins in bone TB pathogenesis.

RESULTS

914 mycobacterial genes were significantly overexpressed and 1688 were repressed in bone TB specimens. Pathway analysis of differentially expressed genes demonstrated a non-replicative and hypometabolic state of M.tb, reinforcement of the mycobacterial cell wall and induction of DNA damage repair responses, suggesting possible survival strategies of M.tb within bone. Bioinformatics mining of microarray data led to identification of five virulence proteins. The genes encoding these proteins were also upregulated in the in vitro MC3T3 osteoblast cell line model of bone TB. Further, exposure of osteoblast cells to two of these virulence proteins (Rv1046c and Rv3663c) significantly inhibited osteoblast differentiation.

CONCLUSION

M.tb alters its transcriptome to establish infection in bone by upregulating certain virulence genes which play a key role in disturbing bone homeostasis.

Osteoclasts: Other functions

Osteoclasts are the only cells that can efficiently resorb bone. They do so by sealing themselves on to bone and removing the mineral and organic components. Osteoclasts are essential for bone homeostasis and are involved in the development of diseases associated with decreased bone mass, like osteoporosis, or abnormal bone turnover, like Paget's disease of bone. In addition, compromise of their development or resorbing machinery is pathogenic in multiple types of osteopetrosis. However, osteoclasts also have functions other than bone resorption. Like cells of the innate immune system, they are derived from myeloid precursors and retain multiple immune cell properties. In addition, there is now strong evidence that osteoclasts regulate osteoblasts through a process known as coupling, which coordinates rates of bone resorption and bone formation during bone remodeling. In this article we review the non-resorbing functions of osteoclasts and highlight their importance in health and disease.

Inflammatory stimuli alter bone marrow composition and compromise bone health in the malnourished host

Inflammation has a role in the pathogenesis of childhood malnutrition. We investigated the effect of malnutrition and inflammatory challenge on bone marrow composition and bone health. We studied an established murine model of moderate acute malnutrition at baseline and after acute inflammatory challenge with bacterial lipopolysaccharide (LPS), a surrogate of Gram-negative bacterial sepsis, or Leishmania donovani, the cause of visceral leishmaniasis. Both of these infections cause significant morbidity and mortality in malnourished children. Of the 2 stimuli, LPS caused more pronounced bone marrow changes that were amplified in malnourished mice. LPS challenge led to increased inflammatory cytokine expression (Il1b, Il6, and Tnf), inflammasome activation, and inflammatory monocyte accumulation in the bone marrow of malnourished mice. Depletion of inflammatory monocytes in Csfr1-LysMcre-DT malnourished mice significantly reduced the inflammasome activation and IL1-ß production after LPS challenge. The inflammatory challenge also led to increased expansion of mesenchymal stem cells (MSCs), bone marrow adiposity, and expression of genes (Pparg, Adipoq, and Srbp1) associated with adipogenesis in malnourished mice. This suggests that inflammatory challenge promotes differentiation of BM MSCs toward the adipocyte lineage rather than toward bone-forming osteoblasts in the malnourished host. Concurrent with this reduced osteoblastic potential there was an increase in bone-resorbing osteoclasts, enhanced osteoclast activity, upregulation of inflammatory genes, and IL-1B involved in osteoclast differentiation and activation. The resulting weakened bone formation and increased bone resorption would contribute to the bone fragility associated with malnutrition. Lastly, we evaluated the effect of replacing lipid rich in omega-6 fatty acids (corn oil) with lipid-rich in omega-3 fatty acids (fish oil) in the nutrient-deficient diet. LPS-challenged malnourished mice that received dietary fish oil showed decreased expression of inflammatory cytokines and Rankl and reduced osteoclast differentiation and activation in the bone marrow. This work demonstrates that the negative effect of inflammatory challenge on bone marrow is amplified in the malnourished host. Increasing dietary intake of omega-3 fatty acids may be a means to reduce inflammation and improve bone health in malnourished children.

Mechanism of COVID-19-Related Proteins in Spinal Tuberculosis: Immune Dysregulation

Purpose

The purpose of this article was to investigate the mechanism of immune dysregulation of COVID-19-related proteins in spinal tuberculosis (STB).

Methods

Clinical data were collected to construct a nomogram model. C-index, calibration curve, ROC curve, and DCA curve were used to assess the predictive ability and accuracy of the model. Additionally, 10 intervertebral disc samples were collected for protein identification. Bioinformatics was used to analyze differentially expressed proteins (DEPs), including immune cells analysis, Gene Ontology (GO) and KEGG pathway enrichment analysis, and protein-protein interaction networks (PPI).

Results

The nomogram predicted risk of STB ranging from 0.01 to 0.994. The C-index and AUC in the training set were 0.872 and 0.862, respectively. The results in the external validation set were consistent with the training set. Immune cells scores indicated that B cells naive in STB tissues were significantly lower than non-TB spinal tissues. Hub proteins were calculated by Degree, Closeness, and MCC methods. The main KEGG pathway included Coronavirus disease-COVID-19. There were 9 key proteins in the intersection of COVID-19-related proteins and hub proteins. There was a negative correlation between B cells naive and RPL19. COVID-19-related proteins were associated with immune genes.

Conclusion

Lymphocytes were predictive factors for the diagnosis of STB. Immune cells showed low expression in STB. Nine COVID-19-related proteins were involved in STB mechanisms. These nine key proteins may suppress the immune mechanism of STB by regulating the expression of immune genes.

Mycobacterium tuberculosis Induced Osteoblast Dysregulation Involved in Bone Destruction in Spinal Tuberculosis

Disturbance of bone homeostasis caused by Mycobacterium tuberculosis (Mtb) is a key clinical manifestation in spinal tuberculosis (TB). However, the complete mechanism of this process has not been established, and an effective treatment target does not exist. Increasing evidence shows that abnormal osteoclastogenesis triggered by an imbalance of the receptor activator of NF-κB ligand (RANKL)/osteoprotegerin (OPG) axis may play a key role in the disturbance of bone homeostasis. Previous studies reported that RANKL is strongly activated in patients with spinal TB; however, the OPG levels in these patients were not investigated in previous studies. In this study, we investigated the OPG levels in patients with spinal TB and the dysregulation of osteoblasts caused by Mtb infection. Inhibition of the Mce4a gene of Mtb by an antisense locked nucleic acid (LNA) gapmer (Mce4a-ASO) was also investigated. Analysis of the serum OPG levels in clinical samples showed that the OPG levels were significantly decreased in patients with spinal TB compared to those in the group of non-TB patients. The internalization of Mtb in osteoblasts, the known major source of OPG, was investigated using the green fluorescent protein (GFP)-labeled Mycobacterium strain H37Ra (H37RaGFP). The cell-associated fluorescence measurements showed that Mtb can efficiently enter osteoblast cells. In addition, Mtb infection caused a dose-dependent increase of the CD40 mRNA expression and cytokine (interleukin 6, IL-6) secretion in osteoblast cells. Ligation of CD40 by soluble CD154 reversed the increased secretion of IL-6. This means that the induced CD40 is functional. Considering that the interaction between CD154-expressing T lymphocytes and bone-forming osteoblast cells plays a pivotal role in bone homeostasis, the CD40 molecule might be a strong candidate for mediating the target for treatment of bone destruction in spinal TB. Additionally, we also found that Mce4a-ASO could dose-dependently inhibit the Mce4a gene of Mtb and reverse the decreased secretion of IL-6 and the impaired secretion of OPG caused by Mtb infection of osteoblast cells. Taken together, the current finding provides breakthrough ideas for the development of therapeutic agents for spinal TB.

Multitasking by the OC Lineage during Bone Infection: Bone Resorption, Immune Modulation, and Microbial Niche

Bone infections, also known as infectious osteomyelitis, are accompanied by significant inflammation, osteolysis, and necrosis. Osteoclasts (OCs) are the bone-resorbing cells that work in concert with osteoblasts and osteocytes to properly maintain skeletal health and are well known to respond to inflammation by increasing their resorptive activity. OCs have typically been viewed merely as effectors of pathologic bone resorption, but recent evidence suggests they may play an active role in the progression of infections through direct effects on pathogens and via the immune system. This review discusses the host- and pathogen-derived factors involved in the in generation of OCs during infection, the crosstalk between OCs and immune cells, and the role of OC lineage cells in the growth and survival of pathogens, and highlights unanswered questions in the field.

Mycobacterium tuberculosis infection increases the number of osteoclasts and inhibits osteoclast apoptosis by regulating TNF-α-mediated osteoclast autophagy

Osteoarticular tuberculosis, a chronic inflammatory disease characterized by Mycobacterium tuberculosis (M.tb) infection, has become a serious problem in China. The present study was conducted to determine the mechanism of action of tumor necrosis factor (TNF)-α in the pathogenesis of osteoarticular tuberculosis. The number of osteoclasts in osteoarticular tuberculosis tissue samples was detected by tartrate-resistant acid phosphatase staining. Autophagy and apoptosis of osteoclasts were detected by western blotting, reverse transcription-quantitative PCR, transmission electron microscopy and TUNEL staining. The results showed that autophagy and the number of osteoclasts increased in the lesions of patients with osteoarticular tuberculosis compared with osteoarthritis samples. Moreover, activation of osteoclast autophagy inhibited the apoptosis of osteoclasts infected with M.tb, and increased the expression level of TNF-α. The results showed that TNF-α enhanced the autophagic activity of M.tb-infected osteoclasts and inhibited cell apoptosis. These findings indicated that M.tb infection induced osteoclast production and inhibited osteoclast apoptosis by regulating TNF-α-mediated osteoclast autophagy, revealing a new mechanism for TNF-α in the pathogenesis of osteoarticular tuberculosis.

Hesperidin methyl chalcone alleviates spinal tuberculosis in New Zealand white rabbits by suppressing immune responses

Objective: Spinal tuberculosis (ST) refers to tuberculosis resulted from infections of Mycobacterium tuberculosis (Mtb) in the spinal cord. Hesperidin methyl chalcone (HMC) is a flavonoid derivative from citrus fruits with anti-inflammatory properties. We aimed to investigate the efficacy of HMC in treating ST in New Zealand white rabbit model. Design and Setting: Rabbits were infected in the sixth lumbar vertebral bodies with or without Mtb strain H37Rv followed by treatments with HMC. Outcome Measures: 10 weeks post treatments, the adjacent vertebral tissues were examined by hematoxylin-eosin staining. The expression levels of transcription factor κB (NF-κB) p65 and monocyte chemoattractant protein-1 (MCP-1/CCL2) in lymphocytes were determined using reverse transcription quantitative real-time PCR (RT-qPCR), Western blot and enzyme-linked immunosorbent assays (ELISA). The serum levels of interleukin (IL)-2, IL-4, IL-10 as well as interferon (IFN)-γ were also assessed using ELISA. Western blot was used to determine the effects of HMC on the phosphorylation of IKKα/β, p65, and IκBα in the signal transduction of NF-κB pathways. Results: HMC significantly attenuated the granulation in adjacent vertebral bone tissues. The expression of p65, IL-4, IL-10, and MCP-1 was reduced. The NF-κB pathway was suppressed, in which the phosphorylation of IκBα, IKKα/β, and p65 was inhibited whereas the relative level of IκBα was increased. Conclusion: HMC could serve as a therapeutic option to effectively inhibit granulomas formation through downregulation of MCP-1, IL-4, IL-10, and NF-κB in the treatment of ST.

Advances in the molecular detection of tuberculosis in pre-contact Andean South America

Andean paleopathological research has significantly enhanced knowledge about the geographical distribution and evolution of tuberculosis (TB) in pre-Columbian South America. In this paper, we review the history and progress of research on ancient tuberculosis (TB) in the Andean region, focusing on the strengths and limitations of current approaches for the molecular detection of ancient pathogens, with special attention to TB. As a case study, we describe a molecular screening approach for the detection of ancient Mycobacterium tuberculosis in individuals from Late Intermediate Period (1000-1400 CE) contexts at the site of Huari, Peru. We evaluate 34 commingled human vertebrae and combine morphological assessments of pathology with high throughput sequencing and a non-selective approach to ancient pathogen DNA screening. Our method enabled the simultaneous detection of ancient M. tuberculosis DNA and an evaluation of the environmental microbial composition of each sample. Our results show that despite the dominance of environmental DNA, molecular signatures of M. tuberculosis were identified in eight vertebrae, six of which had no observable skeletal pathology classically associated tuberculosis infection. This screening approach will assist in the identification of candidate samples for downstream genomic analyses. The method permits higher resolution disease identification in cases where pathology may be absent, or where the archaeological context may necessitate a broad differential diagnosis based on morphology alone.

Interaction of Brucella abortus with Osteoclasts: a Step toward Understanding Osteoarticular Brucellosis and Vaccine Safety

Osteoarticular disease is a frequent complication of human brucellosis. Vaccination remains a critical component of brucellosis control, but there are currently no vaccines for use in humans, and no in vitro models for assessing the safety of candidate vaccines in reference to the development of bone lesions currently exist. While the effect of Brucella infection on osteoblasts has been extensively evaluated, little is known about the consequences of osteoclast infection. Murine bone marrow-derived macrophages were derived into mature osteoclasts and infected with B. abortus 2308, the vaccine strain S19, and attenuated mutants S19vjbR and B. abortus ΔvirB2 While B. abortus 2308 and S19 replicated inside mature osteoclasts, the attenuated mutants were progressively killed, behavior that mimics infection kinetics in macrophages. Interestingly, B. abortus 2308 impaired the growth of osteoclasts without reducing resorptive activity, while osteoclasts infected with B. abortus S19 and S19vjbR were significantly larger and exhibited enhanced resorption. None of the Brucella strains induced apoptosis or stimulated nitric oxide or lactose dehydrogenase production in mature osteoclasts. Finally, infection of macrophages or osteoclast precursors with B. abortus 2308 resulted in generation of smaller osteoclasts with decreased resorptive activity. Overall, Brucella exhibits similar growth characteristics in mature osteoclasts compared to the primary target cell, the macrophage, but is able to impair the maturation and alter the resorptive capacity of these cells. These results suggest that osteoclasts play an important role in osteoarticular brucellosis and could serve as a useful in vitro model for both analyzing host-pathogen interactions and assessing vaccine safety.

The osteoclast, a target cell for microorganisms

Bone is a highly adaptive tissue with regenerative properties that is subject to numerous diseases. Infection is one of the causes of altered bone homeostasis. Bone infection happens subsequently to bone surgery or to systemic spreading of microorganisms. In addition to osteoblasts, osteoclasts (OCs) also constitute cell targets for pathogens. OCs are multinucleated cells that have the exclusive ability to resorb bone mineral tissue. However, the OC is much more than a bone eater. Beyond its role in the control of bone turnover, the OC is an immune cell that produces and senses inflammatory cytokines, ingests microorganisms and presents antigens. Today, increasing evidence shows that several pathogens use OC as a host cell to grow, generating debilitating bone defects. In this review, we exhaustively inventory the bacteria and viruses that infect OC and report the present knowledge in this topic. We point out that most of the microorganisms enhance the bone resorption activity of OC. We notice that pathogen interactions with the OC require further investigation, in particular to validate the OC as a host cell in vivo and to identify the cellular mechanisms involved in altered bone resorption. Thus, we conclude that the OC is a new cell target for pathogens; this new research area paves the way for new therapeutic strategies in the infections causing bone defects.

The NOD-scid IL2rγnull Mouse Model Is Suitable for the Study of Osteoarticular Brucellosis and Vaccine Safety

Osteoarticular brucellosis is the most common complication in Brucella-infected humans regardless of age, sex, or immune status. The mechanism of bone destruction caused by Brucella species remained partially unknown due to the lack of a suitable animal model. Here, to study this complication, we explored the suitability of the use of the NOD-scid IL2rγ^null mouse to study osteoarticular brucellosis and examined the potential use of this strain to evaluate the safety of live attenuated vaccine candidates. Mice were inoculated intraperitoneally with a single dose of 1 × 10⁴, 1 × 10⁵, or 1 × 10⁶ CFU of B. abortus S19 or the vaccine candidate B. abortus S19ΔvjbR and monitored for the development of side effects, including osteoarticular disease, for 13 weeks. Decreased body temperature, weight loss, splenomegaly, and deformation of the tails were observed in mice inoculated with B. abortus S19 but not in those inoculated with S19ΔvjbR Histologically, all S19-inoculated mice had a severe dose-dependent inflammatory response in multiple organs. The inflammatory response at the tail was characterized by the recruitment of large numbers of neutrophils, macrophages, and osteoclasts with marked bone destruction. These lesions histologically resembled what is typically observed in Brucella-infected patients. In contrast, mice inoculated with B. abortus S19ΔvjbR did not show significant bone changes. Immunofluorescence, in situ hybridization, and confocal imaging demonstrated the presence of Brucella at the sites of inflammation, both intra- and extracellularly, and large numbers of bacteria were observed within mature osteoclasts. These results demonstrate the potential use of the NOD-scid IL2rγ^null mouse model to evaluate vaccine safety and further study osteoarticular brucellosis.

Isoliquiritigenin attenuates spinal tuberculosis through inhibiting immune response in a New Zealand white rabbit model

Spinal tuberculosis (ST) is the tuberculosis caused by Mycobacterium tuberculosis (Mtb) infections in spinal curds. Isoliquiritigenin 4,2′,4′-trihydroxychalcone, ISL) is an anti-inflammatory flavonoid derived from licorice (Glycyrrhiza uralensis), a Chinese traditional medicine. In this study, we evaluated the potential of ISL in treating ST in New Zealand white rabbit models. In the model, rabbits (n=40) were infected with Mtb strain H37Rv or not in their 6^th lumbar vertebral bodies. Since the day of infection, rabbits were treated with 20 mg/kg and 100 mg/kg of ISL respectively. After 10 weeks of treatments, the adjacent vertebral bone tissues of rabbits were analyzed through Hematoxylin-Eosin staining. The relative expression of Monocyte chemoattractant protein-1 (MCP-1/CCL2), transcription factor κB (NF-κB) p65 in lymphocytes were verified through reverse transcription quantitative real-time PCR (RT-qPCR), western blotting and enzyme-linked immunosorbent assays (ELISA). The serum level of interleukin (IL)-2, IL-4, IL-10 and interferon γ (IFN-γ) were evaluated through ELISA. The effects of ISL on the phosphorylation of IκBα, IKKα/β and p65 in NF-κB signaling pathways were assessed through western blotting. In the results, ISL has been shown to effectively attenuate the granulation inside adjacent vertebral tissues. The relative level of MCP-1, p65 and IL-4 and IL-10 were retrieved. NF-κB signaling was inhibited, in which the phosphorylation of p65, IκBα and IKKα/β were suppressed whereas the level of IκBα were elevated. In conclusion, ISL might be an effective drug that inhibited the formation of granulomas through downregulating MCP-1, NF-κB, IL-4 and IL-10 in treating ST.

Impaired IFN-α-mediated signal in dendritic cells differentiates active from latent tuberculosis

Individuals exposed to Mycobacterium tuberculosis (Mtb) may be infected and remain for the entire life in this condition defined as latent tuberculosis infection (LTBI) or develop active tuberculosis (TB). Among the multiple factors governing the outcome of the infection, dendritic cells (DCs) play a major role in dictating antibacterial immunity. However, current knowledge on the role of the diverse components of human DCs in shaping specific T-cell response during Mtb infection is limited. In this study, we performed a comparative evaluation of peripheral blood circulating DC subsets as well as of monocyte-derived Interferon-α DCs (IFN-DCs) from patients with active TB, subjects with LTBI and healthy donors (HD). The proportion of circulating myeloid BDCA3⁺ DCs (mDC2) and plasmacytoid CD123⁺ DCs (pDCs) declined significantly in active TB patients compared to HD, whereas the same subsets displayed a remarkable activation in LTBI subjects. Simultaneously, the differentiation of IFN-DCs from active TB patients resulted profoundly impaired compared to those from LTBI and HD individuals. Importantly, the altered developmental trait of IFN-DCs from active TB patients was associated with down-modulation of IFN-linked genes, marked changes in molecular signaling conveying antigen (Ag) presentation and full inability to induce Ag-specific T cell response. Thus, these data reveal an important role of IFN-α in determining the induction of Mtb-specific immunity.

TNFR/TNF-α signaling pathway regulates apoptosis of alveolar macrophages in coal workers' pneumoconiosis

We explored the role of TNFR/TNF-α signalingin apoptosis among alveolar macrophages (AM) and its relevance to the development of coal workers' pneumoconiosis (CWP). Purified alveolar macrophages (AMs) were prepared from bronchoalveolar lavage fluid harvested from 366 CWP patients and 120 healthy subjects enrolled inthe study. The purified AMs were then divided into control, SOD, anti-TNFR, TNFR and NFkB inhibitor groups and analyzed for apoptosis usingflow cytometry (sub-diploid peak) and western blotting (Bcl-2, Caspase-3 and Caspase-8 expression). We found thatAM apoptosis washigher amongCWP patients than thehealthycontrols. Expression ofBcl-2, Caspase-3 and Caspase-8 was higher inAMs from CWP patientsthan in those from the controlsand correlated with increased AM apoptosis. Univariate and multivariate analyses suggested that CWP grade, initial exposure time, exposure time inyears, and CWP onset agewereall associated with altered levels of Bcl-2, Caspase-3 and Caspase-8. Inhibition of TNFR/TNF-α signaling usinganti-TNFR antibody, SOD or NFkB inhibitionreduced AM apoptosisand decreased Bcl-2, Caspase-3 and Caspase-8 expression. These data suggestinhibition of a TNFR/TNF-α signaling pathway is a potentiallyeffective means ofalleviating CWP by inhibiting AM apoptosis.

Roles of monocyte chemotactic protein 1 and nuclear factor-κB in immune response to spinal tuberculosis in a New Zealand white rabbit model

This study aimed to explore the roles of monocyte chemotactic protein 1 (MCP-1) and nuclear factor kappa B (NF-κB) in immune response to spinal tuberculosis in a New Zealand white rabbit model. Forty-eight New Zealand white rabbits were collected and divided into four groups: experimental group (n=30, spinal tuberculosis model was established), the sham group (n=15, sham operation was performed) and the blank group (n=3). The qRT-PCR assay and western blotting were applied to detect the mRNA and protein expressions of MCP-1 and NF-κB in peripheral blood. ELISA was used to measure serum levels of MCP-1, NF-κB, IFN-γ, IL-2, IL-4, and IL-10. Flow cytometry was adopted to assess the distributions of CD4⁺, CD8⁺ lymphocytes and CD4+ CD25+ Foxp3 lymphocyte subsets. Compared with the sham and blank groups, the mRNA and protein expressions of MCP-1 and NF-κB in the experimental group were significantly increased. The experimental group had lower serum levels of IL-2 and IFN-γ and higher serum level of IL-10 than the sham and blank groups. In comparison to the sham and blank groups, CD4⁺ T lymphocyte subsets percentage, CD4⁺/CD8⁺ ratio and CD4⁺ CD25⁺ Foxp3+ Tregs subsets accounting for CD4⁺ lymphocyte in the experimental group were lower, while percentage of CD8⁺ T lymphocyte subsets was higher. Our study provided evidence that higher expression of MCP-1 and NF-κB may be associated with decreased immune function of spinal tuberculosis, which can provide a new treatment direction for spinal tuberculosis.

Strains of Mycobacterium tuberculosis differ in affinity for human osteoblasts and alveolar cells in vitro

Although the lung is the primary site of infection of tuberculosis, Mycobacterium tuberculosis is capable of causing infection at other sites. In 5–10 % such extra-pulmonary tuberculosis is located in bone tissue of the spine. It is unknown whether host or microbial factors are responsible for the site where extra-pulmonary tuberculosis manifests itself. One MDR isolate belonging to strain F28, one susceptible F11 and one isolate each of susceptible, MDR and XDR F15/LAM4/KZN were cultured in Middlebrook 7H9 media. Human osteoblasts (SaOS-2) and human alveolar epithelial cells (A549) were exposed to these different isolates of M. tuberculosis and invasion capacity and intra-cellular multiplication rates were established. Mouse macrophage (MHS) cells exposed to M. tuberculosis H37Rv served as control. The invasion capacity of F15/LAM4/KZN representatives increased with the level of resistance. The F28 MDR strain showed similar invasion capacity as the XDR F15/LAM4/KZN for pulmonary epthelial cells, whilst the fully susceptible F11 strain displayed a propensity for osteoblasts. The differences observed may in part explain why certain strains are able to cause infection at specific extra-pulmonary sites. We postulated that the development of extra-pulmonary tuberculosis depends on the ability of the microbe to pass effectively through the alveolar epithelial lining and its affinity for cells other than those in pulmonary tissue.

Macrophage takeover and the host-bacilli interplay during tuberculosis

Macrophages are key type of antigen-presenting cells that arbitrate the first line of defense against various intracellular pathogens. Tuberculosis, both pulmonary and extrapulmonary, is an infectious disease of global concern caused by Mycobacterium tuberculosis. The bacillus is a highly successful pathogen and has acquired various strategies to downregulate critical innate-effector immune responses of macrophages, such as phagosome-lysosome fusion, autophagy, induction of cytokines, generation of reactive oxygen and nitrogen species and antigen presentation. In addition, the bacilli also subvert acquired immunity. In this review, we aim to provide an overview of different antimycobacterial immune functions of macrophage and the strategies adopted by the bacilli to manipulate these functions to favor its survival and replication inside the host.

Role of cytokines and other factors involved in the Mycobacterium tuberculosis infection

Mycobacterium tuberculosis (Mtb) is a pathogen that is widely distributed geographically and continues to be a major threat to world health. Bacterial virulence factors, nutritional state, host genetic condition and immune response play an important role in the evolution of the infection. The genetically diverse Mtb strains from different lineages have been shown to induce variable immune system response. The modern and ancient lineages strains induce different cytokines patterns. The immunity to Mtb depends on Th1-cell activity [interferon-γ (IFN-γ), interleukin-12 (IL-12) and tumor necrosis factor-α (TNF-α)]. IL-1β directly kills Mtb in murine and human macrophages. IL-6 is a requirement in host resistance to Mtb infection. IFN-γ, TNF-α, IL-12 and IL-17 are participants in Mycobacterium-induced granuloma formation. Other regulating proteins as IL-27 and IL-10 can prevent extensive immunopathology. CXCL 8 enhances the capacity of the neutrophil to kill Mtb. CXCL13 and CCL19 have been identified as participants in the formation of granuloma and control the Mtb infection. Treg cells are increased in patients with active tuberculosis (TB) but decrease with anti-TB treatment. The increment of these cells causes down- regulation of adaptive immune response facilitating the persistence of the bacterial infection. Predominance of Th2 phenotype cytokines increases the severity of TB. The evolution of the Mtb infection will depend of the cytokines network and of the influence of other factors aforementioned.