Toll-like receptor 4 signaling-mediated responses are critically engaged in optimal host protection against highly virulent Mycobacterium tuberculosis K infection

One Health Approach to the Computational Design of a Lipoprotein-Based Multi-Epitope Vaccine Against Human and Livestock Tuberculosis

Tuberculosis (TB) remains a major cause of ill health and one of the leading causes of death worldwide, with about 1.25 million deaths estimated in 2023. Control measures have focused principally on early diagnosis, the treatment of active TB, and vaccination. However, the widespread emergence of anti-tuberculosis drug resistance remains the major public health threat to progress made in global TB care and control. Moreover, the Bacillus Calmette-Guérin (BCG) vaccine, the only licensed vaccine against TB in children, has been in use for over a century, and there have been considerable debates concerning its effectiveness in TB control. A multi-epitope vaccine against TB would be an invaluable tool to attain the Global Plan to End TB 2023-2030 target. A rational approach that combines several B-cell and T-cell epitopes from key lipoproteins was adopted to design a novel multi-epitope vaccine candidate. In addition, interactions with TLR4 were implemented to assess its ability to elicit an innate immune response. The conservation of the selected proteins suggests the possibility of cross-protection in line with the One Health approach to disease control. The vaccine candidate was predicted to be both antigenic and immunogenic, and immune simulation analyses demonstrated its ability to elicit both humoral and cellular immune responses. Protein-protein docking and normal-mode analyses of the vaccine candidate with TLR4 predicted efficient binding and stable interaction. This study provides a promising One Health approach for the design of multi-epitope vaccines against human and livestock tuberculosis. Overall, the designed vaccine candidate demonstrated immunogenicity and safety features that warrant further experimental validation in vitro and in vivo.

Ornithine lipid is a partial TLR4 agonist and NLRP3 activator

Gram-negative bacterial lipopolysaccharides (LPSs) trigger inflammatory reactions through Toll-like receptor 4 (TLR4) and prime myeloid cells for inflammasome activation. In phosphate-limited environments, bacteria reduce LPS and other phospholipid production and synthesize phosphorus-free alternatives such as amino-acid-containing lipids like the ornithine lipid (OL). This adaptive strategy conserves phosphate for other essential cellular processes and enhances bacterial survival in host environments. While OL is implicated in bacterial pathogenicity, the mechanism is unclear. Using primary murine macrophages and human mononuclear cells, we elucidate that OL activates TLR4 and induces potassium efflux-dependent nucleotide-binding domain and leucine-rich repeat-containing pyrin protein 3 (NLRP3) activation. OL upregulates the expression of NLRP3 and pro-interleukin (IL)-1β and induces cytokine secretion in primed and unprimed cells. By contrast, in the presence of LPS, OL functions as a partial TLR4 antagonist and reduces LPS-induced cytokine secretion. We thus suggest that in phosphate-depleted environments, OL replaces LPS bacterial immunogenicity, while constitutively present OL may allow bacteria to escape immune surveillance.

Chronic hyperglycemia impairs anti-microbial function of macrophages in response to Mycobacterium tuberculosis infection

Diabetes mellitus (DM) is a major risk factor for tuberculosis (TB), though the underlying mechanisms linking DM and TB remain ambiguous. Macrophages are a key player in the innate immune response and their phagocytic ability is enhanced in response to microbial infections. Upon infection or inflammation, they also repel invading pathogens by generating; reactive oxygen species (ROS), reactive nitrogen species (RNS), pro-inflammatory cytokines (IL-1β and IL-6), and anti-inflammatory cytokines (IL-10). However, the robustness of these innate defensive capabilities of macrophages when exposed to hyperglycemia remains unclear. In our current work, we explored the production of these host defense molecules in response to challenge with Mycobacterium tuberculosis (Mtb) infection and lipopolysaccharide (LPS) stimulation. Utilizing peritoneal macrophages from high-fat diet + streptozotocin induced diabetic mice and hyperglycemic THP-1-derived macrophages as model systems; we found that LPS stimulation and Mtb infection were ineffective in stimulating the production of ROS, RNS, and pro-inflammatory cytokines in cells exposed to hyperglycemia. On the contrary, an increase in production of anti-inflammatory cytokines was observed. To confirm the mechanism of decreased anti-bacterial activity of the diabetic macrophage, we explored activation status of these compromised macrophages and found decreased surface expression of activation (TLR-4) and differentiation markers (CD11b and CD11c). We postulate that this could be the cause for higher susceptibility for Mtb infection among diabetic individuals.

Identification of ferroptosis-related gene signature for tuberculosis diagnosis and therapy efficacy

Diagnosis of tuberculosis remains a challenge when microbiological tests are negative. Immune cell atlas of patients with tuberculosis and healthy controls were established by single-cell transcriptome. Through integrated analysis of scRNA-seq with microarray and bulk RNA sequencing data, a ferroptosis-related gene signature containing ACSL4, CTSB, and TLR4 genes that were associated with tuberculosis disease was identified. Four gene expression datasets from blood samples of patients with tuberculosis, latent tuberculosis infection, and healthy controls were used to assess the diagnostic value of the gene signature. The areas under the ROC curve for the combined gene signature were 1.000, 0.866, 0.912, and 0.786, respectively, in differentiating active tuberculosis from latent infection. During anti-tuberculosis treatment, the expression of the gene signature decreased significantly in cured patients with tuberculosis. In conclusion, the ferroptosis-related gene signature was associated with tuberculosis treatment efficacy and was a promising biomarker for differentiating active tuberculosis from latent infection.

Toll-like receptor-mediated innate immune responses by recognition of the recombinant dormancy-associated Mycobacterium tuberculosis proteins Rv2659c and Rv1738

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) poses a major threat to the global public health. Importantly, latent tuberculosis infection (LTBI) still impedes the elimination of TB incidence since it has a substantial risk to develop active disease. A multi-stage subunit vaccine comprising active and latency antigens of Mtb has been raised as the promising vaccine to trigger immune protection against all stages of TB. Therefore, the discovery of new antigens that could trigger broad immune response is essential. While current development of TB vaccine mainly focuses on protective immunity mediated by adaptive immune response, the knowledge on triggering the innate immune response by antigens is still limited. We showed that recombinant dormancy-associated Mtb proteins Rv2659c and Rv1738 were recognized by human innate immune recognition molecules, Toll-like receptors (TLRs) 2 and 4 by using HEK-Blue™ hTLR2/hTLR4 systems. We further demonstrated that these two proteins activated phosphorylated NF-κB p65 (Ser536) in the human CD14+ blood cells. We also investigated that these two proteins significantly induced level of pro- and anti-inflammatory cytokines (IL-1β, IL-6, IL-8, IL-10 and TNF-α) which were mediated through TLR2 and TLR4 pathways in human peripheral blood mononuclear cells (hPBMCs). These findings suggest that proteins Rv2659c and Rv1738 stimulated innate immune response targeting TLR2 and TLR4 to produce inflammatory cytokines, and their benefits would be valuable for the development of an effective prophylactic tuberculosis vaccine.

Toll like receptor (2 and 4) expression and cytokine release by human neutrophils during tuberculosis treatment-A longitudinal study

Host innate immune responses to tuberculosis are poorly explored. Recent findings emphasize the importance of innate cells in working against Mycobacterium tuberculosis, the etiologic agent of this deadly disease. In this study we have tried to learn the role of neutrophils in building up immunity against this pathogen during therapy. We isolated neutrophils from peripheral blood of healthy volunteers and pulmonary tuberculosis patients at different phases of their treatment and cultured them withtoll like receptor ligands overnight. Toll like receptor 2 and 4 expression on neutrophils was analyzed using flow cytometry. The supernatants were used to measure cytokines. We found that in tuberculosis patients, expression of TLR2, a proven receptor of Mycobacterium tuberculosis on neutrophils, was increased throughout the duration of therapy (measured at diagnosis, second month and sixth month of therapy). This demonstrates that TLR2 expression is altered as a result of treatment, but not TLR4. Also, the chemokines IL-8 and MIP1α showed a 'dip and raise' fashion as the therapy proceeded. Even though the increase in the pro-inflammatory cytokine secretion by neutrophils seen at the end of therapy is not as expected, it definitely increases our understanding on the function of these cells during TB disease and its resolution and opens new direction in neutrophil research.

Underwhelming or Misunderstood? Genetic Variability of Pattern Recognition Receptors in Immune Responses and Resistance to Mycobacterium tuberculosis

Human genetic control is thought to affect a considerable part of the outcome of infection with Mycobacterium tuberculosis (Mtb). Most of us deal with the pathogen by containment (associated with clinical "latency") or sterilization, but tragically millions each year do not. After decades of studies on host genetic susceptibility to Mtb infection, genetic variation has been discovered to play a role in tuberculous immunoreactivity and tuberculosis (TB) disease. Genes encoding pattern recognition receptors (PRRs) enable a consistent, molecularly direct interaction between humans and Mtb which suggests the potential for co-evolution. In this review, we explore the roles ascribed to PRRs during Mtb infection and ask whether such a longstanding and intimate interface between our immune system and this pathogen plays a critical role in determining the outcome of Mtb infection. The scientific evidence to date suggests that PRR variation is clearly implicated in altered immunity to Mtb but has a more subtle role in limiting the pathogen and pathogenesis. In contrast to 'effectors' like IFN-γ, IL-12, Nitric Oxide and TNF that are critical for Mtb control, 'sensors' like PRRs are less critical for the outcome of Mtb infection. This is potentially due to redundancy of the numerous PRRs in the innate arsenal, such that Mtb rarely goes unnoticed. Genetic association studies investigating PRRs during Mtb infection should therefore be designed to investigate endophenotypes of infection - such as immunological or clinical variation - rather than just TB disease, if we hope to understand the molecular interface between innate immunity and Mtb.

Toll-Like Receptor 4 Protects Against Clostridium perfringens Infection in Mice

Toll-like receptor 4 (TLR4) has been reported to protect against Gram-negative bacteria by acting as a pathogen recognition receptor that senses mainly lipopolysaccharide (LPS) from Gram-negative bacteria. However, the role of TLR4 in Gram-positive bacterial infection is less well understood. Clostridium perfringens type A is a Gram-positive bacterium that causes gas gangrene characterized by severe myonecrosis. It was previously demonstrated that C. perfringens θ-toxin is a TLR4 agonist, but the role of TLR4 in C. perfringens infection is unclear. Here, TLR4-defective C3H/HeJ mice infected with C. perfringens showed a remarkable decrease in survival rate, an increase in viable bacterial counts, and accelerated destruction of myofibrils at the infection site compared with wild-type C3H/HeN mice. These results demonstrate that TLR4 plays an important role in the elimination of C. perfringens. Remarkable increases in levels of inflammatory cytokines, such as interleukin-1β (IL-1β), interleukin-6 (IL-6), and granulocyte colony-stimulating factor (G-CSF), were observed in C. perfringens-infected C3H/HeN mice, whereas the increases were limited in C3H/HeJ mice. Generally, increased G-CSF accelerates granulopoiesis in the bone marrow and the spleen to exacerbate neutrophil production, resulting in elimination of bacteria. The number of neutrophils in the spleen was increased in C. perfringens-infected C3H/HeN mice compared with non-infected mice, while the increase was lower in C. perfringens-infected C3H/HeJ mice. Furthermore, DNA microarray analysis revealed that the mutation in TLR4 partially affects host gene expression during C. perfringens infection. Together, our results illustrate that TLR4 is crucial for the innate ability to eliminate C. perfringens.

Human gene expression profiling identifies key therapeutic targets in tuberculosis infection: A systematic network meta-analysis

Tuberculosis (TB) is one of the deadliest diseases since ancient times and is still a global health problem. So, there is a need to develop new approaches for early detection of TB and understand the host-pathogen relationship. In the present study, we have analyzed microarray data sets and compared the transcriptome profiling of the healthy individual with latent infection (LTBI) and active TB (TB) patients, and identified the differentially expressed genes (DEGs). Next, we performed the systematic network meta-analysis of the DEGs, which identified the seven most influencing hub genes (IL6, IL1B, TNF, NFKB1, STAT1, JAK2, and MAPK8) as the potential therapeutic target in the tuberculosis disease. These target genes are involved in many biological processes like cell cycle control, apoptosis, complement signalling, enhanced cytokine & chemokine signalling, pro-inflammatory responses, and host immune responses. Additionally, we also identified 22 inferred genes that are mainly engaged in the induction of innate immune response, cellular response to interleukin-6, inflammatory response, apoptotic process, I-kappaB-phosphorylation, JAK-STAT signalling pathway, macrophage activation, cell growth, and cell signalling. The proper attention of these inferred genes may open up a new horizon to understand the defensive mechanisms of TB disease. The transcriptome profiling and network approach can enhance the understanding of the molecular pathogenesis of tuberculosis infection and have implications for the plan and execution of mRNA expression tools to support early diagnostics and treatment of Mycobacterium tuberculosis (M.tb).