Engaging the CD40-CD40L pathway augments T-helper cell responses and improves control of Mycobacterium tuberculosis infection

The diagnostic value and validation of IL-22 combimed with sCD40L in tuberculosis pleural effusion

BACKGROUND

There is substantial evidence indicating that cytokines play a role in the immune defense against tuberculosis. This study aims to evaluate the levels of various cytokines in pleural effusion to ditinguish between tuberculosis pleurisy and malignant pleurisy.

METHODS

A total of 82 participants with pleural effusion were included in the training cohort, and 76 participants were included in the validation cohort. The individuals were divided into tuberculosis and malignant pleurisy groups. The concentrations of interleukin-1β (IL-1β), IL-4, IL-6, IL-10, IL-17 A, IL-17 F, IL-21, IL-22, IL-25, IL-31, IL-33, interferon-γ (IFN-γ), soluble CD40 ligand (sCD40L) and tumor necrosis factor-α (TNF-α) in pleural effusion were measured using a multiplex cytokine assay. The threshold values were calculated according to the receiver operating characteristic (ROC) curve analysis to aid in diagnosing tuberculosis pleurisy. Furthermore, the combined measure was validated in the validation cohort.

RESULTS

The levels of all 14 cytokines in pleural effusion were significantly higher in participants with tuberculosis compared to those with malignant pleurisy (all P < 0.05). The area under the curve (AUC) was ≥ 0.920 for the IL-22, sCD40L, IFN-γ, TNF-α and IL-31, which were significantly increased in tuberculous pleural effusion (TPE) compared to MPE in the training cohort. Threshold values of 95.80 pg/mL for IFN-γ, 41.80 pg/mL for IL-31, and 18.87 pg/mL for IL-22 provided ≥ 90% sensitivity and specificity in distinguishing between tuberculosis pleurisy and malignant pleurisy in the training cohort. Among these, IL-22 combined with sCD40L showed the best sensitivity and specificity (94.0% and 96.9%) for diagnosing tuberculosis pleurisy, and this finding was validated in the validation cohort.

CONCLUSION

We demonstrated that the levels of IL-1β, IL-4, IL-6, IL-10, IL-17 A, IL-17 F, IL-21, IL-22, IL-25, IL-31, IL-33, IFN-γ, sCD40L and TNF-α in pleural effusion had significant difference between tuberculosis pleurisy and malignant pleurisy. Specifically, IL-22 ≥ 18.87 pg/mL and sCD40L ≥ 53.08 pg/mL can be clinically utilized as an efficient diagnostic strategy for distinguishing tuberculosis pleurisy from malignant pleurisy.

Vaccination with Mincle agonist UM-1098 and mycobacterial antigens induces protective Th1 and Th17 responses

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is one of the top infectious killers in the world. The only licensed vaccine against TB, Bacille Calmette-Guérin (BCG), provides variable protection against pulmonary TB, especially in adults. Hence, novel TB vaccine approaches are urgently needed. Both Th1 and Th17 responses are necessary for protection against TB, yet effective adjuvants and vaccine delivery systems for inducing robust Th1 and Th17 immunity are lacking. Herein we describe a synthetic Mincle agonist, UM-1098, and a silica nanoparticle delivery system that drives Th1/Th17 responses to Mtb antigens. Stimulation of human peripheral blood mononuclear cells (hPBMCs) with UM-1098 induced high levels of Th17 polarizing cytokines IL-6, IL-1β, IL-23 as well as IL-12p70, IL-4 and TNF-α in vitro. PBMCs from both C57BL/6 and BALB/c mice responded with a similar cytokine pattern in vitro and in vivo. Importantly, intramuscular (I.M.) vaccination with UM-1098-adjuvanted TB antigen M72 resulted in significantly higher antigen-specific IFN-γ and IL-17A levels in C57BL/6 wt mice than Mincle KO mice. Vaccination of C57BL/6 wt mice with immunodominant Mtb antigens ESAT6/Ag85B or M72 resulted in predominantly Th1 and Th17 responses and induced antigen-specific serum antibodies. Notably, in a virulent Mtb challenge model, vaccination with UM-1098 adjuvanted ESAT6/Ag85B or M72 significantly reduced lung bacterial burden when compared with unvaccinated mice and protection occurred in the absence of pulmonary inflammation. These data demonstrate that the synthetic Mincle agonist UM-1098 induces strong Th1 and Th17 immunity after vaccination with Mtb antigens and provides protection against Mtb infection in mice.

CD4-mediated immunity shapes neutrophil-driven tuberculous pathology

Pulmonary Mycobacterium tuberculosis (Mtb) infection results in highly heterogeneous lesions ranging from granulomas with central necrosis to those primarily comprised of alveolitis. While alveolitis has been associated with prior immunity in human post-mortem studies, the drivers of these distinct pathologic outcomes are poorly understood. Here, we show that these divergent lesion structures can be modeled in C3HeB/FeJ mice and are regulated by prior immunity. Using quantitative imaging, scRNAseq, and flow cytometry, we demonstrate that Mtb infection in the absence of prior immunity elicits dysregulated neutrophil recruitment and necrotic granulomas. In contrast, prior immunity induces rapid recruitment and activation of T cells, local macrophage activation, and diminished late neutrophil responses. Depletion studies at distinct infection stages demonstrated that neutrophils are required for early necrosis initiation and necrosis propagation at chronic stages, whereas early CD4 T cell responses prevent neutrophil feedforward circuits and necrosis. Together, these studies reveal fundamental determinants of tuberculosis lesion structure and pathogenesis, which have important implications for new strategies to prevent or treat tuberculosis.

Analyzing human CD4+ T cells activated in response to macrophages infected with Mycobacterium tuberculosis

M1- and M2-like macrophages infected with Mycobacterium tuberculosis (Mtb) have been found to differ in their capacity to elicit memory CD4+ T cell activation. Here, we present a protocol to quantify and isolate the subset of human memory CD4+ T cells activated in response to autologous monocyte-derived macrophages (MDMs) infected with virulent Mtb. We describe steps for CD14+ monocyte isolation, generating MDMs, culturing Mtb and infection of macrophages, and identifying activated CD4+ T cells by flow cytometry. For complete details on the use and execution of this protocol, please refer to Gail et al.1.

The role of the Notch signaling pathway in bacterial infectious diseases

The Notch signaling pathway is the most crucial link in the normal operation and maintenance of physiological functions of mammalian life processes. Notch receptors interact with ligands and this leads to three cleavages and goes on to enter the nucleus to initiate the transcription of target genes. The Notch signaling pathway deeply participates in the differentiation and function of various cells, including immune cells. Recent studies indicate that the outcomes of Notch signaling are changeable and highly dependent on different bacterial infection. The Notch signaling pathway plays a different role in promoting and inhibiting bacterial infection. In this review, we focus on the latest research findings of the Notch signaling pathway in bacterial infectious diseases. The Notch signaling pathway is critically involved in a variety of development processes of immunosuppression of different APCs. The Notch signaling pathway leads to functional changes in epithelial cells to aggravate tissue damage. Specifically, we illustrate the regulatory mechanism of the Notch signaling pathway in various bacterial infections, such as Mycobacterium tuberculosis, Mycobacterium avium paratuberculosis, Mycobacterium leprae, Helicobacter pylori, Klebsiella pneumoniae, Bacillus subtilis, Staphylococcus aureus, Ehrlichia chaffeensis and sepsis. Collectively, this review will not only help beginners intuitively and systematically understand the Notch signaling pathway in bacterial infectious diseases but also help experts to generate fresh insight in this field.

From immunology to artificial intelligence: revolutionizing latent tuberculosis infection diagnosis with machine learning

Latent tuberculosis infection (LTBI) has become a major source of active tuberculosis (ATB). Although the tuberculin skin test and interferon-gamma release assay can be used to diagnose LTBI, these methods can only differentiate infected individuals from healthy ones but cannot discriminate between LTBI and ATB. Thus, the diagnosis of LTBI faces many challenges, such as the lack of effective biomarkers from Mycobacterium tuberculosis (MTB) for distinguishing LTBI, the low diagnostic efficacy of biomarkers derived from the human host, and the absence of a gold standard to differentiate between LTBI and ATB. Sputum culture, as the gold standard for diagnosing tuberculosis, is time-consuming and cannot distinguish between ATB and LTBI. In this article, we review the pathogenesis of MTB and the immune mechanisms of the host in LTBI, including the innate and adaptive immune responses, multiple immune evasion mechanisms of MTB, and epigenetic regulation. Based on this knowledge, we summarize the current status and challenges in diagnosing LTBI and present the application of machine learning (ML) in LTBI diagnosis, as well as the advantages and limitations of ML in this context. Finally, we discuss the future development directions of ML applied to LTBI diagnosis.

Blocking CD40 Alleviates Th1 and Th17 Cell Responses in Elastin Peptide-Induced Murine Emphysema

Purpose

To investigate the role of the CD40-CD40 ligand (CD40L) pathway in the regulation of Th1, Th17, and regulatory T (Treg)-cell responses in an elastin peptide (EP)-induced autoimmune emphysema mouse model.

Methods

BALB/c mice were transnasally treated with EP on day 0, injected intravenously with anti-CD40 antibody via the tail vein on day 33, and sacrificed on day 40. The severity of emphysema was evaluated by determining the mean linear intercept (MLI) and destructive index (DI) from lung sections. The proportions of myeloid dendritic cells (mDCs) and Th1, Th17, and Treg cells in the blood, spleen, and lungs were determined via flow cytometry. The levels of the cytokines interleukin (IL)-6, IL-17, interferon (IFN)-γ, and transforming growth factor (TGF)-β were detected via enzyme-linked immunosorbent assay. Ifnγ, IL17a, Rorγt and Foxp3 transcription levels were detected via polymerase chain reaction.

Results

CD40+ mDCs accumulated in the lungs of EP-stimulated mice. Blocking the CD40-CD40L pathway with an anti-CD40 antibody alleviated Th1 and Th17 responses; increased the proportion of Treg cells; decreased MLI and DI; reduced the levels of cytokines IL-6, IL-17, and IFN-γ as well as the transcription levels of Ifnγ, IL17a, and Rorγt; and upregulated the expression of TGF-β and Foxp3.

Conclusion

The CD40-CD40L pathway could play a critical role in Th1, Th17 and Treg cell dysregulation in EP-mediated emphysema and could be a potential therapeutic target.

OMIP-096: A 24-color flow cytometry panel to identify and characterize CD4+ and CD8+ tissue-resident T cells in human skin, intestinal, and type II mucosal tissue

There is a great need to understand human immune cells within tissue, where disease manifests and infection occurs. Tissue-resident memory T cells (TRMs) were discovered over a decade ago, there is a great need to understand their role in human disease. We developed a 24-color flow cytometry panel to comprehensively interrogate CD4+ and CD8+ TRMs isolated from human tissues. When interrogating cells within human tissue, enzymatic methods used to liberate cells from within the tissue can cause cleavage of cell surface markers needed to phenotype these cells. Here we carefully select antibody clones and evaluate the effect of enzymatic digestion on the expression of markers relevant to the identification of T cell residency, as well as markers relevant to the activation and immunoregulation status of these cells. We have designed this panel to be applicable across a range of human tissues including skin, intestine, and type II mucosae such as the vagina.

Tweaking host immune responses for novel therapeutic approaches against Mycobacterium tuberculosis

In TB, combat between the human host and Mycobacterium tuberculosis involves intricate interactions with immune cells. M. tuberculosis has evolved a complex evasion system to circumvent immune cells, leading to persistence and limiting its clearance by the host. Host-directed therapies are emerging approaches to modulate host responses, including inflammatory responses, cytokine responses, and autophagy, by using small molecules to curb mycobacterial infections. Targeting host immune pathways reduces the chances of antibiotic resistance to M. tuberculosis because, unlike antibiotics, this approach acts directly on the cells of the host. In this review, we discuss the role of immune cells during M. tuberculosis proliferation, provide a updated understanding of immunopathogenesis, and explore the range of host-modulating options for the clearance of this pathogen.

TB granuloma: CD30 co-stimulation for CD4+ T cell co-operation

Tuberculosis granuloma T cells express an array of mediators including the CD30 co-stimulatory receptor and its ligand, CD153. CD4 T effector cells require signals through CD30, potentially provided co-operatively by other T cells, to completely differentiate and protect against disease (Foreman et al., 2023. J. Exp. Med.https://doi.org/10.1084/jem.20222090).

Blood monocyte and dendritic cell profiles among people living with HIV with Mycobacterium tuberculosis co-infection

BACKGROUND

Understanding the complex interactions of the immune response mediated by Mycobacterium tuberculosis and HIV co-infection is fundamental to disease biomarker discovery, vaccine, and drug development. Using flow cytometry, we characterized the frequencies and phenotypic differences in monocytes and dendritic cell populations using peripheral blood mononuclear cells from individuals with recurrent, active pulmonary tuberculosis with and without coexisting HIV infection (CAPRISA 011, Clinicaltrials.gov, NCT02114684, 29/01/2014) and compared them to samples from HIV positive individuals and healthy controls. Additionally, we assessed the associations between the frequency of monocyte and dendritic cell subsets and time to culture conversion and cavitary disease in patients with active TB using a cox proportional hazards and logistic regression models.

RESULTS

Compared to healthy controls, the frequency of total monocytes (HLA-DR + CD14 +) was significantly higher in the TB/HIV and TB groups and the frequency of dendritic cells (HLA-DR + CD14-) was significantly higher in TB/HIV and HIV groups. We observed significant variation in the expression of CCR2, CD40, CD11b, CD86, CD163, CX3CR1 across different cell subsets in the four study groups. Increase in CCR2, CD11b and CD40 was associated with active TB infection, while decrease in CX3CR1 and increase in CD163 was associated with HIV infection. Expression of CX3CR1 (aHR 0.98, 95% CI 0.963 - 0.997, p = 0.019) on non-classical monocytes associated with longer time to TB culture conversion in the multivariable model correcting for randomization arm, age, sex, HIV status, lung cavitation, alcohol use, smoking and BMI. Higher surface expression of CD86 (aOR 1.017, 95% CI 1.001 - 1.032, p = 0.033) on intermediate monocytes associated with the presence of lung cavitation, while higher expression of transitional monocytes (aOR 0.944, 95% CI 0.892 - 0.999, p = 0.047) associated with the absence of lung cavitation in the multivariable model.

CONCLUSION

These data provide valuable insight into the heterogenous role of monocyte and dendritic cells in TB and HIV infections.

Glucose metabolism and its role in the maturation and migration of human CD1c+ dendritic cells following exposure to BCG

Introduction

Tuberculosis (TB) still kills over 1 million people annually. The only approved vaccine, BCG, prevents disseminated disease in children but shows low efficacy at preventing pulmonary TB. Myeloid dendritic cells (mDCs) are promising targets for vaccines and immunotherapies to combat infectious diseases due to their essential role in linking innate and adaptive immune responses. DCs undergo metabolic reprogramming following exposure to TLR agonists, which is thought to be a prerequisite for a successful host response to infection. We hypothesized that metabolic rewiring also plays a vital role in the maturation and migration of DCs stimulated with BCG. Consequently, we investigated the role of glycolysis in the activation of primary human myeloid CD1c⁺ DCs in response to BCG.

Methods/results

We show that CD1c⁺ mDC mature and acquire a more energetic phenotype upon challenge with BCG. Pharmacological inhibition of glycolysis with 2-deoxy-D-glucose (2-DG) decreased cytokine secretion and altered cell surface expression of both CD40 and CCR7 on BCG-challenged, compared to untreated, mDCs. Furthermore, inhibition of glycolysis had differential effects on infected and uninfected bystander mDCs in BCG-challenged cultures. For example, CCR7 expression was increased by 2-DG treatment following challenge with BCG and this increase in expression was seen only in BCG-infected mDCs. Moreover, although 2-DG treatment inhibited CCR7-mediated migration of bystander CD1C⁺ DCs in a transwell assay, migration of BCG-infected cells proceeded independently of glycolysis.

Discussion

Our results provide the first evidence that glycolysis plays divergent roles in the maturation and migration of human CD1c⁺ mDC exposed to BCG, segregating with infection status. Further investigation of cellular metabolism in DC subsets will be required to determine whether glycolysis can be targeted to elicit better protective immunity against Mtb.

Immune checkpoint modulating T cells and NK cells response to Mycobacterium tuberculosis infection

Many subversive mechanisms promote the occurrence and development of chronic infectious diseases and cancer, among which the down-regulated expression of immune-activating receptors and the enhanced expression of immune-inhibitory receptors accelerate the occurrence and progression of the disease. Recently, the use of immune checkpoint inhibitors has shown remarkable efficacy in the treatment of tumors in multiple organs. However, the expression of immune checkpoint molecules on natural killer (NK) cells by Mycobacterium tuberculosis (Mtb) infection and its impact on NK cell effector functions have been poorly studied. In this review, we focus on what is currently known about the expression of various immune checkpoints in NK cells following Mtb infection and how it alters NK cell-mediated host cytotoxicity and cytokine secretion. Unraveling the function of NK cells after the infection of host cells by Mtb is crucial for a comprehensive understanding of the innate immune mechanism of NK cells involved in tuberculosis and the evaluation of the efficacy of immunotherapies using immune checkpoint inhibitors to treat tuberculosis. In view of some similarities in the immune characteristics of T cells and NK cells, we reviewed the molecular mechanism of the interaction between T cells and Mtb, which can help us to further understand and explore the specific interaction mechanism between NK cells and Mtb.

B21 DNA vaccine expressing ag85b, rv2029c, and rv1738 confers a robust therapeutic effect against latent Mycobacterium tuberculosis infection

Latent tuberculosis infection (LTBI) treatment is known to accelerate the decline in TB incidence, especially in high-risk populations. Mycobacterium tuberculosis (M. tb) expression profiles differ at different growth periods, and vaccines protective and therapeutic effects may increase when they include antigenic compositions from different periods. To develop a post-exposure vaccine that targets LTBI, we constructed four therapeutic DNA vaccines (A39, B37, B31, and B21) using different combinations of antigens from the proliferation phase (Ag85A, Ag85B), PE/PPE family (Rv3425), and latent phase (Rv2029c, Rv1813c, Rv1738). We compared the immunogenicity of the four DNA vaccines in C57BL/6j mice. The B21 vaccine stimulated the strongest cellular immune responses, namely Th1/Th17 and CD8⁺ cytotoxic T lymphocyte responses. It also induced the generation of strengthened effector memory and central memory T cells. In latently infected mice, the B21 vaccine significantly reduced bacterial loads in the spleens and lungs and decreased lung pathology. In conclusion, the B21 DNA vaccine can enhance T cell responses and control the reactivation of LTBI.

Central nervous system infection caused by Mycobacterium houstonense: A case report

Background

Mycobacterium houstonense is a rapidly growing mycobacterium (RGM) that belongs to the unnamed third biovariant complex of the Mycobacterium fortuitum group, which is rarely responsible for human infection. Approximately 76% of infections caused by the M. fortuitum group occur after open fractures or skin, soft tissue, bone, or puncture wounds. To date, only a few cases of human infectious disease caused by M. houstonense have been reported worldwide.

Case presentation

We present a case of a 26-year-old man with a central nervous system (CNS) infection caused by M. houstonense. The patient was transferred to our hospital because of headaches and muscle strength changes. One month prior to presentation at our hospital, the patient was diagnosed with tuberculous meningitis at the other two hospitals, but his condition did not improve after anti-tuberculous treatment, antibiotics, and anti-viral treatment before admission to our hospital. Lumbar puncture was performed at both previous hospitals, as well as at our hospital; the results consistently indicated high cerebrospinal fluid (CSF) opening pressure. M. houstonense was detected in the CSF of the second hospital's lumbar puncture by metagenomic next-generation sequencing (mNGS) but was not identified at our hospital. The patient was discharged from our hospital after receiving non-tuberculous mycobacterium (NTM) treatment for 1 month according to the Chinese NTM guidelines. However, the patient died 20 days after discharge.

Conclusion

Since it is difficult to identify M. houstonense, this is the first case of human CNS infection caused by M. houstonense in China. This case may be considered by neurologists and infectious physicians when CNS infection does not respond to conventional treatment, especially in the uncommon type of NTM.

Tuberculosis dissemination in kidney transplant recipient treated with anti-CD40 monoclonal antibody: a case report

Background

Tuberculosis (TBC) in solid organ transplant recipients represents a severe complication. The incidence among transplant recipients is higher than in the general population, and the diagnosis and treatment remain challenging. We present a case of active disseminated tuberculosis in a kidney transplant recipient treated with an anti-CD40 monoclonal antibody, who had been previously exposed to an active form of the disease, but latent tuberculosis (LTBI) was repeatedly ruled out prior to transplantation. To the best of our knowledge, no other case has been reported in a patient treated with the anti-CD40 monoclonal antibody.

Case presentation

A 49-year-old patient, 1.5 years after primary kidney transplantation, presented with vocal cord problems, a dry irritating cough, and a sore throat. A detailed investigation, including a high-resolution chest CT scan, revealed the diagnosis of disseminated tuberculosis. The antituberculosis treatment consisting of rifampicin, isoniazid, pyrazinamide, and ethambutol was started immediately. The patient's condition became complicated by relapsing diarrhoea. The colonoscopy revealed a circular stenosis above Bauhin’s valve. Microscopical findings showed active colitis and vaguely formed collections of epithelioid macrophages without fully developed caseous granulomas and were consistent with the clinical diagnosis of tuberculosis. The antituberculosis treatment was subsequently enhanced by moxifloxacin and led to a great improvement in the patient’s condition.

Conclusion

In this case, false negativity of interferon-γ release assays and possibly higher risk for intracellular infections in patients on costimulatory signal blockers are discussed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-022-02916-2.

Pathological and protective roles of dendritic cells in Mycobacterium tuberculosis infection: Interaction between host immune responses and pathogen evasion

Dendritic cells (DCs) are principal defense components that play multifactorial roles in translating innate immune responses to adaptive immunity in Mycobacterium tuberculosis (Mtb) infections. The heterogeneous nature of DC subsets follows their altered functions by interacting with other immune cells, Mtb, and its products, enhancing host defense mechanisms or facilitating pathogen evasion. Thus, a better understanding of the immune responses initiated, promoted, and amplified or inhibited by DCs in Mtb infection is an essential step in developing anti-tuberculosis (TB) control measures, such as host-directed adjunctive therapy and anti-TB vaccines. This review summarizes the recent advances in salient DC subsets, including their phenotypic classification, cytokine profiles, functional alterations according to disease stages and environments, and consequent TB outcomes. A comprehensive overview of the role of DCs from various perspectives enables a deeper understanding of TB pathogenesis and could be useful in developing DC-based vaccines and immunotherapies.

RANTES and CD40L under Conditions of Long-Term Physical Exercise: A Potential Link to Adaptive Immunity

Regular physical exercise was found to be associated with an improved immune response in previous studies. RANTES and CD40L play a pivotal role in host defense, and individuals lacking adequate expression are prone to virus and opportunistic infections. A total of 98 participants were enrolled in this study. The probands were asked to perform moderate physical activity, and bicycle stress tests were performed at the baseline and after 8 months of training to evaluate individual performance. RANTES and CD40L were found to be increased by long-term physical exercise. In particular, probands with a performance gain of ≥3% displayed a pronounced elevation of both markers, paired with a decrease in circulating IL6 levels and an improved lipid profile. In summary, we were able to highlight rising levels of serum RANTES and CD40L under the conditions of physical exercise. Taking their role in host defense into account, a conjunction of physical activity and the adaptive immune system could therefore be assumed. Furthermore, low inflammatory profiles in probands with a significant performance gain suggest a modulation through exercise rather than a generalized pro-inflammatory status.

Mycobacterium tuberculosis impedes CD40-dependent notch signaling to restrict Th17 polarization during infection

Early Th₁₇ responses are necessary to provide protection against Mycobacterium tuberculosis (Mtb). Mtb impedes Th₁₇ polarization by restricting CD40 co-stimulatory pathway on dendritic cells (DCs). We previously demonstrated that engaging CD40 on DCs increased Th₁₇ responses. However, the molecular mechanisms that contributed to Th₁₇ polarization were unknown. Here, we identify the Notch ligand DLL4 as necessary for Th₁₇ polarization and demonstrate that Mtb limits DLL4 on DCs to prevent optimal Th₁₇ responses. Although Mtb infection induced only low levels of DLL4, engaging CD40 on DCs increased DLL4 expression. Antibody blockade of DLL4 on DCs reduced Th₁₇ polarization in vitro and in vivo. In addition, we show that the Mtb Hip1 protease attenuates DLL4 expression on lung DCs by impeding CD40 signaling. Overall, our results demonstrate that Mtb impedes CD40-dependent DLL4 expression to restrict Th₁₇ responses and identify the CD40-DLL4 pathways as targets for developing new Th₁₇-inducing vaccines and adjuvants for tuberculosis.

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Mtb restricts Th₁₇ responses by impairing CD40 signaling on dendritic cells

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Engaging CD40 on DCs increases Notch ligand Dll4 transcript and surface expression

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DLL4 is necessary for polarizing Th₁₇ and multifunctional T cells in the lungs of mice

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Mtb impairs CD40/DLL4 pathway through the Hip1 serine protease immune evasion protein

Dendritic Cells and Their Immunotherapeutic Potential for Treating Type 1 Diabetes

Type 1 diabetes (T1D) results from the destruction of pancreatic beta cells through a process that is primarily mediated by T cells. Emerging evidence suggests that dendritic cells (DCs) play a crucial role in initiating and developing this debilitating disease. DCs are professional antigen-presenting cells with the ability to integrate signals arising from tissue infection or injury that present processed antigens from these sites to naïve T cells in secondary lymphoid organs, thereby triggering naïve T cells to differentiate and modulate adaptive immune responses. Recent advancements in our knowledge of the various subsets of DCs and their cellular structures and methods of orchestration over time have resulted in a better understanding of how the T cell response is shaped. DCs employ various arsenal to maintain their tolerance, including the induction of effector T cell deletion or unresponsiveness and the generation and expansion of regulatory T cell populations. Therapies that suppress the immunogenic effects of dendritic cells by blocking T cell costimulatory pathways and proinflammatory cytokine production are currently being sought. Moreover, new strategies are being developed that can regulate DC differentiation and development and harness the tolerogenic capacity of these cells. Here, in this report, we focus on recent advances in the field of DC immunology and evaluate the prospects of DC-based therapeutic strategies to treat T1D.

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.

Immune responses to bacterial lung infections and their implications for vaccination

The pulmonary immune system plays a vital role in protecting the delicate structures of gaseous exchange against invasion from bacterial pathogens. With antimicrobial resistance becoming an increasing concern, finding novel strategies to develop vaccines against bacterial lung diseases remains a top priority. In order to do so, a continued expansion of our understanding of the pulmonary immune response is warranted. Whilst some aspects are well characterised, emerging paradigms such as the importance of innate cells and inducible immune structures in mediating protection provide avenues of potential to rethink our approach to vaccine development. In this review, we aim to provide a broad overview of both the innate and adaptive immune mechanisms in place to protect the pulmonary tissue from invading bacterial organisms. We use specific examples from several infection models and human studies to depict the varying functions of the pulmonary immune system that may be manipulated in future vaccine development. Particular emphasis has been placed on emerging themes that are less reviewed and underappreciated in vaccine development studies.

T-Cell Exhaustion in Mycobacterium tuberculosis and Nontuberculous Mycobacteria Infection: Pathophysiology and Therapeutic Perspectives

Immune exhaustion is a condition associated with chronic infections and cancers, characterized by the inability of antigen-specific T cells to eliminate the cognate antigen. Exhausted T cells display a peculiar phenotypic profile and exclusive functional characteristics. Immune exhaustion has been described in patients with Mycobacterium tuberculosis infection, and cases of tuberculosis reactivation have been reported in those treated with immune checkpoint inhibitors, drugs able to re-establish T-cells’ function. Exhausted T CD8⁺ cells’ profile has also been described in patients with infection due to nontuberculous mycobacteria. In this review, we initially provide an overview of the mechanisms leading to immune exhaustion in patients infected by Mycobacterium tuberculosis and nontuberculous mycobacteria. We then dissect the therapeutic perspectives related to immune checkpoint blockade in patients with these infections.

Macrophages Are the Key Players in Promoting Hyper-Inflammatory Response in a Mouse Model of TB-IRIS

TB-IRIS is an abnormal inflammatory response in a subset of HIV-TB co-infected patients shortly after initiation of anti-retroviral therapy (ART). Therapy in these patients could have greatly improved the life expectancy as ART reconstitutes the function and number of CD4+ T cells and many patients see improvement in symptoms but paradoxically up to 54% of co-infected patients develop TB-IRIS. Different studies have indicated that both innate and adaptive immunity are involved in the pathology of IRIS but the role of macrophages in abnormal activation of CD4+ T cells is poorly understood. Since macrophages are one of the major antigen-presenting cells and are infected by M.tb at a high frequency, they are very much likely to be involved in the development of TB-IRIS. In this study, we have developed a mouse model of experimental IRIS, in which M.tb-infected T-cell knockout mice undergo a fatal inflammatory disease after CD4+ T cell reconstitution. Lung macrophages and blood monocytes from M.tb-infected TCRβ-/- mice showed upregulated expression of cell surface activation markers and also showed higher mRNA expression of inflammation-associated chemokines and matrix metalloproteases responsible for tissue damage. Furthermore, cytokine and TLR signaling feedback mechanism to control excessive inflammation was also found to be dysregulated in these macrophages under lymphopenic conditions. Previous studies have shown that hyperactive CD4+ T cells are responsible for disease induction and our study shows that somehow macrophages are in a higher activated state when infected with M.tb in an immune-deficient condition, which results in excessive activation of the adoptively transferred CD4+ T cells. Understanding of the mechanisms underlying the pathophysiology of TB-IRIS would facilitate identification of prospective biomarkers for disease development in HIV-TB co-infected patients before starting antiretroviral therapy.

Advancing Adjuvants for Mycobacterium tuberculosis Therapeutics

Tuberculosis (TB) remains one of the leading causes of death worldwide due to a single infectious disease agent. BCG, the only licensed vaccine against TB, offers limited protection against pulmonary disease in children and adults. TB vaccine research has recently been reinvigorated by new data suggesting alternative administration of BCG induces protection and a subunit/adjuvant vaccine that provides close to 50% protection. These results demonstrate the need for generating adjuvants in order to develop the next generation of TB vaccines. However, development of TB-targeted adjuvants is lacking. To help meet this need, NIAID convened a workshop in 2020 titled “Advancing Vaccine Adjuvants for Mycobacterium tuberculosis Therapeutics”. In this review, we present the four areas identified in the workshop as necessary for advancing TB adjuvants: 1) correlates of protective immunity, 2) targeting specific immune cells, 3) immune evasion mechanisms, and 4) animal models. We will discuss each of these four areas in detail and summarize what is known and what we can advance on in order to help develop more efficacious TB vaccines.

Role of IL-6 in dendritic cell functions

Dendritic cells (DCs) are efficient antigen-presenting cells that serve as a link between the innate and adaptive immune systems. These cells are broadly involved in cellular and humoral immune responses by presenting antigens to initiate T cell reactions, cytokine and chemokine secretion, T cell differentiation and expansion, B cell activation and regulation, and the mediation of immune tolerance. The functions of DCs depend on their activation status, which is defined by the stages of maturation, phenotype differentiation, and migration ability, among other factors. IL-6 is a soluble mediator mainly produced by a variety of immune cells, including DCs, that exerts pleiotropic effects on immune and inflammatory responses through interaction with specific receptors expressed on the surface of target cells. Here, we review the role of IL-6, when generated in an inflammatory context or as derived from DCs, in modulating the biologic function and activation status of DCs and emphasize the importance of searching for novel strategies to target the IL-6/IL-6 signaling pathway as a means to diminish the inflammatory activity of DCs in immune response or to prime the immunogenic activity of DCs in immunosuppressive conditions.

Developing smarter vaccines for paratuberculosis: From early biomarkers to vaccine design

Vaccines for paratuberculosis have been used for over a hundred years but the disease continues to affect ruminant health and livestock industries globally. Mycobacterium avium subspecies paratuberculosis which causes the disease also known as Johne's disease is a subversive pathogen able to undermine both innate and adaptive host defense mechanisms. This review focuses on early protective immune pathways that lead to some animals becoming resilient to infection to provide a road map for designing better vaccines and emphasizes the need for harnessing the potential of mucosal immunity.

CD40 induces an antimicrobial response against the intracellular pathogen Streptococcus agalactiae in Nile tilapia, Oreochromis niloticus

Streptococcus agalactiae is a Gram-positive facultative intracellular bacterium that leads to severe economic loss of tilapia worldwide. Previous studies demonstrated that CD40 contributes to host protection against intracellular injection. In this study, CD40 was characterized from Nile tilapia (Oreochromis niloticus), named OnCD40. Sequence analysis showed that open reading frame of OnCD40 was 933 bp, containing a single peptide, a transmembrane domain and four cysteine-rich domains. The qRT-PCR revealed that OnCD40 was expressed in all examined tissues with the most abundant ones in spleen and thymus. After S. agalactiae stimulation, the expression of OnCD40 was significantly induced in most of the detected organs. Moreover, OnCD40-overexpressing fish elicited significant protection against subsequent S. agalactiae challenge; approximately 10000-fold fewer bacteria were detected in spleen of OnCD40-overexpressing fish in comparison with control fish. Thus, CD40 had protecting function in Nile tilapia against intracellular pathogens.

Development of a Broadly Protective, Self-Adjuvanting Subunit Vaccine to Prevent Infections by Pseudomonas aeruginosa

Infections caused by the opportunistic pathogen Pseudomonas aeruginosa can be difficult to treat due to innate and acquired antibiotic resistance and this is exacerbated by the emergence of multi-drug resistant strains. Unfortunately, no licensed vaccine yet exists to prevent Pseudomonas infections. Here we describe a novel subunit vaccine that targets the P. aeruginosa type III secretion system (T3SS). This vaccine is based on the novel antigen PaF (Pa Fusion), a fusion of the T3SS needle tip protein, PcrV, and the first of two translocator proteins, PopB. Additionally, PaF is made self-adjuvanting by the N-terminal fusion of the A1 subunit of the mucosal adjuvant double-mutant heat-labile enterotoxin (dmLT). Here we show that this triple fusion, designated L-PaF, can activate dendritic cells in vitro and elicits strong IgG and IgA titers in mice when administered intranasally. This self-adjuvanting vaccine expedites the clearance of P. aeruginosa from the lungs of challenged mice while stimulating host expression of IL-17A, which may be important for generating a protective immune response in humans. L-PaF's protective capacity was recapitulated in a rat pneumonia model, further supporting the efficacy of this novel fusion vaccine.

The importance of T cell-derived cytokines in post-kala-azar dermal leishmaniasis

Infection with the same species of Leishmania (L)donovani causes different manifestations including visceral leishmaniasis (VL) and post kala-azar dermal leishmaniasis (PKDL), indicating that the host-related immunological parameters perform a decisive role in the pathogenesis of diseases. As PKDL is a reservoir of the parasite, a better understanding of the host immune responses is necessary to restrict the L. donovani transmission. The proper local production of Th1 cell-related cytokines (including IFN-γ, TNF-α and IL-12), Th17 cell-derived cytokines (such as IL-17A, IL-17F and IL-22), and CD8⁺ cytotoxic T lymphocyte (CTL)-derived IFN-γ are protective against PKDL. However, dominant production of regulatory CD4⁺ T cell-derived cytokines (such as IL-10 and TGF-β), Th2 cell-derived cytokines (such as IL-4/IL-13), M2 macrophage-derived cytokines (such as IL-4 and IL-10), keratinocyte-derived IL-10, regulatory CD8⁺ T cell-derived IL-10, and dendritic cell-derived IL-10, IL-27 and IL-21 can contribute to the parasite persistence and PKDL development. Understanding of the T cell-related cytokine network within PKDL lesions gives rise to novel insights concerning the role of each cytokine in the protection or susceptibility to disease. Manipulation of the cytokine network can be considered as an interesting immunotherapeutic strategy for the treatment of L. donovani-mediated PKDL.

March of Mycobacterium: miRNAs intercept host cell CD40 signalling

The disease tuberculosis is fatal if untreated. It is caused by the acid-fast bacilli Mycobacterium tuberculosis. Mycobacterium resides and replicates within the alveolar macrophages, causing inflammation and granuloma, wherein macrophage-T cell interactions enhance the inflammation-causing pulmonary caseous lesions. The first interactions between Mycobacterium and the receptors on macrophages decide the fate of Mycobacterium because of phagolysosomal impairments and the expression of several miRNAs, which may regulate CD40 expression on macrophages. While the altered phagolysosomal functions impede antigen presentation to the T cell-expressed antigen receptor, the interactions between the macrophage-expressed CD40 and the T cell-expressed CD40-ligand (CD40L or CD154) provide signals to T cells and Mycobacterium-infected macrophages. These two functions significantly influence the resolution or persistence of Mycobacterium infection. CD40 controls T-cell polarisation and host-protective immunity by eliciting interleukin-12p40, nitric oxide, reactive oxygen species and IFN-γ production. Indeed, CD40-deficient mice succumb to low-dose aerosol infection with Mycobacterium because of deficient interleukin (IL)-12 production leading to impaired IFN-γ-secreting T-cell response. In contrast, despite generating fewer granulomas, the CD40L-deficient mice developed anti-mycobacterial T-cell responses to the levels observed in the wild-type mice. These host-protective responses are significantly subdued by the Mycobacterium-infected macrophage produced TGF-β and IL-10, which promote pro-mycobacterial T-cell responses. The CD40-CD40L-induced counteractive immune responses against Mycobacterium thus present a conundrum that we explain here with a reconciliatory hypothesis. Experimental validation of the hypothesis will provide a rationale for designing anti-tubercular immunotherapy.

Tuberculosis-Cancer Parallels in Immune Response Regulation

Mycobacterium tuberculosis and cancer are two diseases with proclivity for the development of resistance to the host immune system. Mechanisms behind resistance can be host derived or disease mediated, but they usually depend on the balance of pro-inflammatory to anti-inflammatory immune signals. Immunotherapies have been the focus of efforts to shift that balance and drive the response required for diseases eradication. The immune response to tuberculosis has widely been thought to be T cell dependent, with the majority of research focused on T cell responses. However, the past decade has seen greater recognition of the importance of the innate immune response, highlighting factors such as trained innate immunity and macrophage polarization to mycobacterial clearance. At the same time, there has been a renaissance of immunotherapy treatments for cancer since the first checkpoint inhibitor passed clinical trials, in addition to work highlighting the importance of innate immune responses to cancer. However, there is still much to learn about host-derived responses and the development of resistance to new cancer therapies. This review examines the similarities between the immune responses to cancer and tuberculosis with the hope that their commonalities will facilitate research collaboration and discovery.

Pulmonary Mycobacterium tuberculosis control associates with CXCR3- and CCR6-expressing antigen-specific Th1 and Th17 cell recruitment

Mycobacterium tuberculosis-specific (M. tuberculosis-specific) T cell responses associated with immune control during asymptomatic latent tuberculosis infection (LTBI) remain poorly understood. Using a nonhuman primate aerosol model, we studied the kinetics, phenotypes, and functions of M. tuberculosis antigen-specific T cells in peripheral and lung compartments of M. tuberculosis-infected asymptomatic rhesus macaques by longitudinally sampling blood and bronchoalveolar lavage, for up to 24 weeks postinfection. We found substantially higher frequencies of M. tuberculosis-specific effector and memory CD4+ and CD8+ T cells producing IFN-γ in the airways compared with peripheral blood, and these frequencies were maintained throughout the study period. Moreover, M. tuberculosis-specific IL-17+ and IL-17+IFN-γ+ double-positive T cells were present in the airways but were largely absent in the periphery, suggesting that balanced mucosal Th1/Th17 responses are associated with LTBI. The majority of M. tuberculosis-specific CD4+ T cells that homed to the airways expressed the chemokine receptor CXCR3 and coexpressed CCR6. Notably, CXCR3+CD4+ cells were found in granulomatous and nongranulomatous regions of the lung and inversely correlated with M. tuberculosis burden. Our findings provide insights into antigen-specific T cell responses associated with asymptomatic M. tuberculosis infection that are relevant for developing better strategies to control TB.

Anti-CD40 monoclonal antibody ameliorates experimental autoimmune uveoretinitis in mice

OBJECTIVE

To investigate the effects of CD40 on ocular inflammation in experimental autoimmune uveoretinitis (EAU) in B10.RIII mice.

ANIMALS STUDIED

EAU-susceptible B10.RIII mice were subcutaneously immunized with interphotoreceptor retinoid-binding protein (IRBP) 161-180 in complete Freund's adjuvant and evaluated clinically and pathologically on days 7, 14, 21, 28, and 35 postimmunization. Anti-CD40 antibody was intraperitoneally injected into mice every other day from days 7 to 14 postimmunization. Phosphate-buffered saline (PBS)-injected EAU mice were used as the controls.

PROCEDURES

The frequencies of CD11c⁺ CD40⁺ dendritic cells (DCs), CD11c⁺ MHC-II⁺ DCs, and CD11c⁺ CD40⁺ MHC-II⁺ DCs in splenocytes were evaluated by flow cytometry on days 0, 7, 14, and 21 after immunization. Tumor necrosis factor (TNF)-α and interleukin (IL)-6 production in CD11c⁺ DCs was assessed by ELISA. IRBP-specific lymphocyte proliferation was assessed using a modified MTT cell proliferation assay.

RESULTS

The number of CD11c⁺ CD40⁺ DCs, CD11c⁺ MHC-II⁺ DCs, and CD11c⁺ CD40⁺ MHC-II⁺ DCs increased at the onset of EAU, peaked at the height of disease severity, and was sustained at a high level until day 21. Treatment with anti-CD40 antibody significantly alleviated clinical and pathological activities related to EAU. Compared with the control mice, antibody-treated EAU mice showed few CD11c⁺ CD40⁺ DC and CD11c⁺ CD40⁺ MHC-II⁺ DC frequencies in splenocytes. The anti-CD40 antibody significantly suppressed IRBP-specific lymphocyte proliferation and TNF-α and IL-6 production by DCs in EAU mice.

CONCLUSIONS

The increased expression of CD40 and major histocompatibility complex (MHC) class II molecules in the splenocytes of EAU mice were correlated with inflammatory activity. Anti-CD40 treatment can significantly attenuate EAU activity by inhibiting systemic IRBP-specific immune responses.

Fighting Persistence: How Chronic Infections with Mycobacterium tuberculosis Evade T Cell-Mediated Clearance and New Strategies To Defeat Them

Chronic bacterial infections are caused by pathogens that persist within their hosts and avoid clearance by the immune system. Treatment and/or detection of such pathogens is difficult, and the resulting pathologies are often deleterious or fatal. There is an urgent need to develop protective vaccines and host-directed therapies that synergize with antibiotics to prevent pathogen persistence and infection-associated pathologies. However, many persistent pathogens, such as Mycobacterium tuberculosis, actively target the very host pathways activated by vaccination. These immune evasion tactics blunt the effectiveness of immunization strategies and are impeding progress to control these infections throughout the world. Therefore, it is essential that M. tuberculosis immune evasion-related pathogen virulence strategies are considered to maximize the effectiveness of potential new treatments. In this review, we focus on how Mycobacterium tuberculosis infects antigen-presenting cells and evades effective immune clearance by the adaptive response through (i) manipulating antigen presentation, (ii) repressing T cell-activating costimulatory molecules, and (iii) inducing ligands that drive T cell exhaustion. In this context, we will examine the challenges that bacterial virulence strategies pose to developing new vaccines. We will then discuss new approaches that will help dissect M. tuberculosis immune evasion mechanisms and devise strategies to bypass them to promote long-term protection and prevent disease progression.

Immunology of Mycobacterium tuberculosis Infections

Tuberculosis (TB) is a serious global public health challenge that results in significant morbidity and mortality worldwide. TB is caused by infection with the bacilli Mycobacterium tuberculosis (M. tuberculosis), which has evolved a wide variety of strategies in order to thrive within its host. Understanding the complex interactions between M. tuberculosis and host immunity can inform the rational design of better TB vaccines and therapeutics. This chapter covers innate and adaptive immunity against M. tuberculosis infection, including insights on bacterial immune evasion and subversion garnered from animal models of infection and human studies. In addition, this chapter discusses the immunology of the TB granuloma, TB diagnostics, and TB comorbidities. Finally, this chapter provides a broad overview of the current TB vaccine pipeline.

The CD200-CD200R cross-talk helps Leishmania donovani to down regulate macrophage and CD4+CD44+ T cells effector functions in an NFκB independent manner

The lacuna in the knowledge of immunobiology, especially in visceral infections that are fatal if left untreated, are a major hurdle in getting a vaccine candidate for leishmaniasis. Till date, only a few drugs are available to combat human leishmaniasis and a vaccine candidate either prophylactic or preventive is still awaited. Therefore, identification of host and parasitic factors involved in the regulation of specific immune mechanisms are essentially needed. In this study, we observed that CD200-CD200R immune inhibitory axis regulates host macrophages effectors properties and helps antigen experienced T cells (CD4⁺CD44⁺ T cells) to acquire anti-inflammatory cytokines (IL-4, IL-10, TGF-β, IL-27) producing abilities in an NFkB independent manner. After CD200 blocking the macrophages effectively inhibited proliferation of Leishmania amastigotes and also induced the production of IL-12, IFN-γ, TNF-α and nitric oxide (NOx). Further, the blocking of CD200 signaling also restored macrophages MHC-II expression and helped CD4⁺CD44⁺ T cells to produce pro-inflammatory cytokines like IL-2, IL-12 and IFN-γ. The finding of this study suggested the importance of immune inhibitory mechanisms in controlling Leishmania growth and survival and therefore, requires more studies to understand its role in vaccine induced immunity.

IL-10 Dampens the Th1 and Tc Activation through Modulating DC Functions in BCG Vaccination

BCG, the only registered vaccine against Mycobacterial Tuberculosis (TB) infection, has been questioned for its protective efficacy for decades. Although lots of efforts were made to improve the BCG antigenicity, few studies were devoted to understand the role of host factors in the variability of the BCG protection. Using the IL-10KO mice and pulmonary tuberculosis infection model, we have addressed the role of IL-10 in the BCG vaccination efficacy. The data showed that IL-10-deficient dendritic cells (DCs) could promote the immune responses through upregulation of the surface costimulatory molecule expression and play an orchestra role through activating CD4⁺T cell. IL-10-deficient mice had higher IFN γ, TNF α, and IL-6 production after BCG vaccination, which was consistent with the higher proportion of IFN γ⁺CD3⁺, IFN γ⁺CD4⁺, and IFN γ⁺CD8⁺ T cells in the spleen. Particularly, the BCG-vaccinated IL-10KO mice showed less inflammation after TB challenge compared to WT mice, which was supported by the promoted Th1 and Tc, as well as the downregulated Treg responses in IL-10 deficiency. In a conclusion, we demonstrated the negative relationship between Th1/Tc responses with IL-10 production. IL-10 deficiency restored the type 1 immune response through DC activation, which provided better protection against TB infection. Hence, our study offers the first experimental evidence that, contrary to the modulation of BCG, host immunity plays a critical role in the BCG protective efficacy against TB.

Nilotinib: A Tyrosine Kinase Inhibitor Mediates Resistance to Intracellular Mycobacterium Via Regulating Autophagy

Nilotinib, a tyrosine kinase inhibitor, has been studied extensively in various tumor models; however, no information exists about the pharmacological action of nilotinib in bacterial infections. Mycobacterium bovis (M. bovis) and Mycobacterium avium subspecies paratuberculosis (MAP) are the etiological agents of bovine tuberculosis and Johne's disease, respectively. Although M. bovis and MAP cause distinct tissue tropism, both of them infect, reside, and replicate in mononuclear phagocytic cells of the infected host. Autophagy is an innate immune defense mechanism for the control of intracellular bacteria, regulated by diverse signaling pathways. Here we demonstrated that nilotinib significantly inhibited the intracellular survival and growth of M. bovis and MAP in macrophages by modulating host immune responses. We showed that nilotinib induced autophagic degradation of intracellular mycobacterium occurred via the inhibition of PI3k/Akt/mTOR axis mediated by abelson (c-ABL) tyrosine kinase. In addition, we observed that nilotinib promoted ubiquitin accumulation around M. bovis through activation of E3 ubiquitin ligase parkin. From in-vivo experiments, we found that nilotinib effectively controlled M. bovis growth and survival through enhanced parkin activity in infected mice. Altogether, our data showed that nilotinib regulates protective innate immune responses against intracellular mycobacterium, both in-vitro and in-vivo, and can be exploited as a novel therapeutic remedy for the control of M. bovis and MAP infections.

The Mycobacterium tuberculosis glycoprotein Rv1016c protein inhibits dendritic cell maturation, and impairs Th1 /Th17 responses during mycobacteria infection

The myobacterial factors and the associated mechanism by which Mycobacterium tuberculosis (Mtb) evades the host immune surveillance system remain widely unexplored. Here, we found that overexpressing Rv1016c, a mannosylated protein of M. tuberculosis in BCG (rBCG-Rv1016c) led to increased virulence of the recombined BCG in the severe-combined immunodeficient (SCID) mice model and to a loss of protective efficacy in a zebrafish-M. marinum model, compared to wild type BCG. Further investigations on the effects of rBCG-Rv1016c on the host innate immunity revealed that rBCG-Rv1016c decreased the production of cytokines IL-2, IL-12p70, TGF-β, IL-6 as well as of the co-stimulatory molecules CD80, CD86, MHC-I and MHC-II by the infected DCs. These effects were mimicked by rBCG-Rv1016cHis, which carried an extra 6-His tag at the C-terminus of Rv1016c. Relatively to BCG infected DCs, the rBCG-Rv1016c-infected DCs failed to polarize naïve T cells to Th1- and Th17-type cells to secret IFN-γ and IL-17. Additionally, T lymphocytes from BCG- infected mice showed significantly less proliferation and production of IFN-γ and IL-17. Similarly, rBCG-Rv1016c mice released a higher level of IL-10 in response to rBCG-Rv1016c stimulation than wild type BCG infected mice. Furthermore, DCs from TLR-2 knockout mice showed no reduction in IL-6, IL-12 p70 and TGF-β secretion in response to rBCG-Rv1016c infection, compared to DCs infected with BCG. We propose that Rv1016c interferes in differentiation of the DCs by targeting suppressor of cytokine signaling (SOCS) 1 and SOCS3 expression, which subsequently leads to the reduction in STAT-1 and STAT-6 phosphorylation. These findings open new perspectives regarding the immunosuppressive strategies adopted by Mtb to survive in the host.

Immune Response to Mycobacterium tuberculosis: A Narrative Review

The encounter between Mycobacterium tuberculosis (Mtb) and the host leads to a complex and multifaceted immune response possibly resulting in latent infection, tubercular disease or to the complete clearance of the pathogen. Macrophages and CD4⁺ T lymphocytes, together with granuloma formation, are traditionally considered the pillars of immune defense against Mtb and their role stands out clearly. However, there is no component of the immune system that does not take part in the response to this pathogen. On the other side, Mtb displays a complex artillery of immune-escaping mechanisms capable of responding in an equally varied manner. In addition, the role of each cellular line has become discussed and uncertain further than ever before. Each defense mechanism is based on a subtle balance that, if altered, can lean to one side to favor Mtb proliferation, resulting in disease progression and on the other to the host tissue damage by the immune system itself. Through a brief and complete overview of the role of each cell type involved in the Mtb response, we aimed to highlight the main literature reviews and the most relevant studies in order to facilitate the approach to such a complex and changeable topic. In conclusion, this narrative mini-review summarizes the various immunologic mechanisms which modulate the individual ability to fight Mtb infection taking in account the major host and pathogen determinants in the susceptibility to tuberculosis.

Evaluation of the expression of cytokines and chemokines in macrophages in response to rifampin-monoresistant Mycobacterium tuberculosis and H37Rv strain

Macrophages are the primary phagocytes in the lungs and a part of the host defense system against Mycobacterium tuberculosis (Mtb), involved in the primary immune response. While several studies have assessed the effects of resistance to rifampin on Mtb physiology, the consequences of mutations in genes encoding the beta subunit of RNA polymerase (rpoB) for host-pathogen interactions remain poorly understood. In this study, rifampin-monoresistant (RMR) Mtb and H37Rv strains were used to infect the THP-1-derived macrophages. Real-time quantitative reverse transcription PCR assay was carried out to determine mRNA expression in 84 cytokine and chemokine genes. Production of specific cytokines and chemokines was measured by ELISA assay. In conclusion, the current study shed more light on the fitness cost of RMR strain and the potential effects of rpoB gene mutations on Mtb-host interactions. These results initially demonstrate that the Mtb carrying the rpoB-S450L can modulate macrophage responses to mediate bacterial survival.

Mycobacterial glycolipid Di-O-acyl trehalose promotes a tolerogenic profile in dendritic cells

Due to prolonged coevolution with the human being, Mycobacterium tuberculosis has acquired a sophisticated capacity to evade host immunity and persist in a latent state in the infected individual. As part of this evolutive process, mycobacteria have developed a highly complex cell wall that acts as a protective barrier. Herein we studied the effects of Di-O-acyl trehalose, a cell-wall glycolipid of virulent mycobacteria on murine bone marrow-derived dendritic cells. We have demonstrated that Di-O-Acyl-trehalose promotes a tolerogenic phenotype in bone marrow-derived murine DCs activated with mycobacterial antigens and Toll-like receptor agonists. This phenotype included low expression of antigen presentation and costimulatory molecules and altered cytokine production with downregulation of IL-12 and upregulation of IL-10, an anti-inflammatory cytokine. Additional markers of tolerogenicity were the expression of Indoleamine 2,3-dioxygenase and CD25. Furthermore, Di-O-Acyl-Trehalose promoted the expansion of FoxP3+ regulatory T lymphocytes. A better understanding of mycobacterial cell-wall components involved in the evasion of immunity is a prerequisite to designing better strategies to fight tuberculosis.

Subpopulation Structure of IFNγ-Producing T Lymphocytes in Patients with Pulmonary Tuberculosis

The study of subpopulation structure of IFNγ-producing T cells in patients with pulmonary tuberculosis revealed a decrease in the number of CD3⁺ IFNγ⁺ cells against the background of significantly increased IFNγ secretion in vitro irrespective of the clinical form of the disease and drug sensitivity of M. tuberculosis, most strongly expressed in case of the disseminated tuberculosis. In patients with infiltrative drug-sensitive and drug-resistant pulmonary tuberculosis, increased number of Th1/Th17 lymphocytes (CD4⁺ IFNγ⁺IL-17A⁺) and, conversely, decreased number of blood γδT cells was detected.

Friends and foes of tuberculosis: modulation of protective immunity

Protective immunity in tuberculosis (TB) is subject of debate in the TB research community, as this is key to fully understand TB pathogenesis and to develop new promising tools for TB diagnosis and prognosis as well as a more efficient TB vaccine. IFN-γ producing CD4+ T cells are key in TB control, but may not be sufficient to provide protection. Additional subsets have been identified that contribute to protection such as multifunctional and cytolytic T-cell subsets, including classical and nonclassical T cells as well as novel innate immune cell subsets resulting from trained immunity. However, to define protective immune responses against TB, the complexity of balancing TB immunity also has to be considered. In this review, insights into effector cell immunity and how this is modulated by regulatory cells, associated comorbidities and the host microbiome, is discussed. We systematically map how different suppressive immune cell subsets may affect effector cell responses at the local site of infection. We also dissect how common comorbidities such as HIV, helminths and diabetes may bias protective TB immunity towards pathogenic and regulatory responses. Finally, also the composition and diversity of the microbiome in the lung and gut could affect host TB immunity. Understanding these various aspects of the immunological balance in the human host is fundamental to prevent TB infection and disease.

Deletion of BCG Hip1 protease enhances dendritic cell and CD4 T cell responses

Dendritic cells (DCs) play a key role in the generation of CD4 T cell responses to pathogens. Mycobacterium tuberculosis (Mtb) harbors immune evasion mechanisms that impair DC responses and prevent optimal CD4 T cell immunity. The vaccine strain Mycobacterium bovis Bacille Calmette-Guérin (BCG) shares many of the immune evasion proteins utilized by Mtb, but the role of these proteins in DC and T cell responses elicited by BCG is poorly understood. We previously reported that the Mtb serine protease, Hip1, promotes sub-optimal DC responses during infection. Here, we tested the hypothesis that BCG Hip1 modulates DC functions and prevents optimal antigen-specific CD4 T cell responses that limit the immunogenicity of BCG. We generated a strain of BCG lacking hip1 (BCGΔhip1) and show that it has superior capacity to induce DC maturation and cytokine production compared with the parental BCG. Furthermore, BCGΔhip1-infected DCs were more effective at driving the production of IFN-γ and IL-17 from antigen-specific CD4 T cells in vitro. Mucosal transfer of BCGΔhip1-infected DCs into mouse lungs induced robust CD4 T cell activation in vivo and generated antigen-specific polyfunctional CD4 T cell responses in the lungs. Importantly, BCGΔhip1-infected DCs enhanced control of pulmonary bacterial burden following Mtb aerosol challenge compared with the transfer of BCG-infected DCs. These results reveal that BCG employs Hip1 to impair DC activation, leading to attenuated lung CD4 T cell responses with limited capacity to control Mtb burden after challenge.