Pulmonary tuberculosis patients with a vitamin D deficiency demonstrate low local expression of the antimicrobial peptide LL-37 but enhanced FoxP3+ regulatory T cells and IgG-secreting cells

Reinventing the human tuberculosis (TB) granuloma: Learning from the cancer field

Tuberculosis (TB) remains one of the deadliest infectious diseases in the world and every 20 seconds a person dies from TB. An important attribute of human TB is induction of a granulomatous inflammation that creates a dynamic range of local microenvironments in infected organs, where the immune responses may be considerably different compared to the systemic circulation. New and improved technologies for in situ quantification and multimodal imaging of mRNA transcripts and protein expression at the single-cell level have enabled significantly improved insights into the local TB granuloma microenvironment. Here, we review the most recent data on regulation of immunity in the TB granuloma with an enhanced focus on selected in situ studies that enable spatial mapping of immune cell phenotypes and functions. We take advantage of the conceptual framework of the cancer-immunity cycle to speculate how local T cell responses may be enhanced in the granuloma microenvironment at the site of Mycobacterium tuberculosis infection. This includes an exploratory definition of "hot", immune-inflamed, and "cold", immune-excluded TB granulomas that does not refer to the level of bacterial replication or metabolic activity, but to the relative infiltration of T cells into the infected lesions. Finally, we reflect on the current knowledge and controversy related to reactivation of active TB in cancer patients treated with immune checkpoint inhibitors such as PD-1/PD-L1 and CTLA-4. An understanding of the underlying mechanisms involved in the induction and maintenance or disruption of immunoregulation in the TB granuloma microenvironment may provide new avenues for host-directed therapies that can support standard antibiotic treatment of persistent TB disease.

Reduced vitamin D-induced cathelicidin production and killing of Mycobacterium tuberculosis in macrophages from a patient with a non-functional vitamin D receptor: A case report

Tuberculosis (TB) presents a serious health problem with approximately a quarter of the world’s population infected with Mycobacterium tuberculosis (M. tuberculosis) in an asymptomatic latent state of which 5–10% develops active TB at some point in their lives. The antimicrobial protein cathelicidin has broad antimicrobial activity towards viruses and bacteria including M. tuberculosis. Vitamin D increases the expression of cathelicidin in many cell types including macrophages, and it has been suggested that the vitamin D-mediated antimicrobial activity against M. tuberculosis is dependent on the induction of cathelicidin. However, unraveling the immunoregulatory effects of vitamin D in humans is hampered by the lack of suitable experimental models. We have previously described a family in which members suffer from hereditary vitamin D-resistant rickets (HVDRR). The family carry a mutation in the DNA-binding domain of the vitamin D receptor (VDR). This mutation leads to a non-functional VDR, meaning that vitamin D cannot exert its effect in family members homozygous for the mutation. Studies of HVDRR patients open unique possibilities to gain insight in the immunoregulatory roles of vitamin D in humans. Here we describe the impaired ability of macrophages to produce cathelicidin in a HVDRR patient, who in her adolescence suffered from extrapulmonary TB. The present case is a rare experiment of nature, which illustrates the importance of vitamin D in the pathophysiology of combating M. tuberculosis.

Evaluation of circulating serum cathelicidin levels as a potential biomarker to discriminate between active and latent tuberculosis in Uganda

Background

Tuberculosis remains a major public health problem worldwide accounting for 1.4 million deaths annually. LL-37 is an effector molecule involved in immunity with both antimicrobial and immunomodulatory properties. The purpose of this study was to compare LL-37 circulatory levels among participants with active and latent tuberculosis and to determine its ability to discriminate between the two infectious states.

Methods

A cross-sectional study was performed among 56 active tuberculosis patients, 49 latent tuberculosis individuals, and 43 individuals without tuberculosis infection. The enzyme-linked immunosorbent assay was used to assess LL-37 levels. Data analysis was performed using STATA software and Graph pad Prism version 8. Mann-Whitney U test was used for correlation between variables with two categories and the Kruskal-Wallis test for three or more categories.

Results

The study had more female participants than males, with similar median ages across the three groups, 29.5, 25.0, and 23.0 years respectively. Active tuberculosis patients had significantly higher LL-37 levels compared to those with latent tuberculosis and without tuberculosis. The median/interquartile ranges were 318.8 ng/ml (157.9–547.1), 242.2 ng/ml (136.2–579.3), 170.9 ng/ml (129.3–228.3); p = 0.002 respectively. Higher LL-37 was found in the male participant with median/interquartile range, 424.8 ng/ml (226.2–666.8) compared to the females 237.7 ng/ml (129.6–466.6); p = 0.045. LL-37 had better discriminatory potential between active tuberculosis and no tuberculosis (AUC = 0.71, sensitivity 71.4% specificity = 69.8%) than with latent tuberculosis (AUC = 0.55, sensitivity = 71.4%, specificity = 44.9%). There was moderate differentiation between latent tuberculosis and no tuberculosis (AUC = 0.63, sensitivity = 44.9% specificity = 90.7%).

Conclusion

Significantly higher LL-37 levels were observed among active tuberculosis patients than those without tuberculosis infection and were, therefore able to discriminate between active tuberculosis and other tuberculosis infectious states, especially with no tuberculosis. Further assessment of this biomarker as a screening tool to exclude tuberculosis is required.

Immunosuppressive Features of the Microenvironment in Lymph Nodes Granulomas from Tuberculosis and HIV-Co-Infected Patients

Tuberculosis (TB) and HIV co-infection claims many lives every year. This study assessed immune responses in Mycobacterium tuberculosis-infected lymph node tissues from HIV-negative and HIV-positive patients compared with the peripheral circulation with a focus on myeloid cells and the cell-signaling enzymes, inducible nitric oxide synthase, and arginase (Arg)-1. Methods included immunohistochemistry or confocal microscopy and computerized image analyses, quantitative real-time PCR, multiplex Luminex, and flow cytometry. These findings indicate enhanced chronic inflammation and immune activation in TB/HIV co-infection but also enhanced immunosuppressive responses. Poorly formed necrotic TB granulomas with a high expression of M. tuberculosis antigens were elevated in TB/HIV-co-infected lymph nodes, and inducible nitric oxide synthase and Arg-1 expression was significantly higher in TB/HIV-co-infected compared with HIV-negative TB or control tissues. High Arg-1 expression was found in myeloid cells with a phenotype characteristic of myeloid-derived suppressor cells (MDCS) that were particularly abundant in TB/HIV-co-infected tissues. Accordingly, Lin-/HLA-DRlow/int/CD33+/CD11b+/CD15+ granulocytic myeloid-derived suppressor cells were significantly elevated in blood samples from TB/HIV-co-infected patients. CD15+ myeloid-derived suppressor cells correlated with plasma HIV viral load and M. tuberculosis antigen load in tissue but were inversely associated with peripheral CD4 T-cells counts. Enhanced chronic inflammation driven by M. tuberculosis and HIV co-infection may promote Arg-1-expressing MDSCs at the site of infection thereby advancing TB disease progression.

Resveratrol, EGCG and Vitamins Modulate Activated T Lymphocytes

Vitamins and bioactives, which are constituents of the food chain, modulate T lymphocyte proliferation and differentiation, antibody production, and prevent inflammation and autoimmunity. We investigated the effects of vitamins (vitamin A (VA), D (VD), E (VE)) and bioactives (i.e., resveratrol (Res), epigallocatechin-3-gallate (EGCG)) on the adaptive immune response, as well as their synergistic or antagonistic interactions. Freshly isolated T lymphocytes from healthy individuals were activated with anti-CD3/CD28 antibodies for 4–5 days in the presence of bioactives and were analyzed by cytofluorometry. Interleukins, cytokines, and chemokines were measured by multiple ELISA. Gene expression was measured by quantitative RT-PCR. Res and EGCG increased CD4 surface intensity. EGCG led to an increased proportion of CD8⁺ lymphocytes. Anti-CD3/CD28 activation induced exuberant secretion of interleukins and cytokines by T lymphocyte subsets. VD strongly enhanced T_h2 cytokines (e.g., IL-5, IL-13), whereas Res and EGCG favored secretion of T_h1 cytokines (e.g., IL-2, INF-γ). Res and VD mutually influenced cytokine production, but VD dominated the cytokine secretion pattern. The substances changed gene expression of interleukins and cytokines in a similar way as they did secretion. Collectively, VD strongly modulated cytokine and interleukin production and favored T_h2 functions. Resveratrol and EGCG promoted the T_h1 response. VA and VE had only a marginal effect, but they altered both T_h1 and T_h2 response. In vivo, bioactives might therefore interact with vitamins and support the outcome and extent of the adaptive immune response.

Retinoic acid induces antimicrobial peptides and cytokines leading to Mycobacterium tuberculosis elimination in airway epithelial cells

Tuberculosis (TB) is the leading cause of death by a single infectious agent, Mycobacterium tuberculosis (Mtb). Alveolar macrophages and respiratory epithelial cells are the first cells exposed to Mtb during the primary infection, once these cells are activated, secrete cytokines and antimicrobial peptides that are associated with the Mtb contention and elimination. Vitamins are micronutrients that function as boosters on the innate immune system, however, is unclear whether they have any protective activity during Mtb infection. Thus, we investigated the role of vitamin A (retinoic acid), vitamin C (ascorbic acid), vitamin D (calcitriol), and vitamin E (alfa-tocopherol) as inductors of molecules related to mycobacterial infection in macrophages and epithelial cells. Our results showed that retinoic acid promotes the expression of pro- and anti-inflammatory molecules such as Thymic stromal lymphopoietin (TSLP), β-defensin-2, IL-1β, CCL20, β-defensin-3, Cathelicidin LL-37, TGF-β, and RNase 7, whereas calcitriol, ascorbic acid, and α-tocopherol lead to an anti-inflammatory response. Treatment of Mtb-infected epithelial cells and macrophage-like cells with the vitamins showed a differential response, where calcitriol reduced Mtb in macrophages, while retinoic acid reduced infection in epithelial cells. Thereby, we propose that a combination of calcitriol and retinoic acid supplementation can drive the immune response, and promotes the Mtb elimination by increasing the expression of antimicrobial peptides and cytokines, while simultaneously modulating inflammation.

Impact of vitamin D status and cathelicidin antimicrobial peptide on adults with active pulmonary TB globally: A systematic review and meta-analysis

BACKGROUND

Tuberculosis remains a global threat and a public health problem that has eluded attempts to eradicate it. Low vitamin D levels have been identified as a risk factor for tuberculosis infection and disease. The human cathelicidin LL-37 has both antimicrobial and immunomodulatory properties and is dependent on vitamin D status. This systematic review attempts to compare vitamin D andLL-37 levels among adult pulmonary tuberculosis patients to non-pulmonary TB individuals between 16-75 years globally and to determine the association between vitamin D and cathelicidin and any contributing factor among the two study groups.

METHODS/DESIGN

We performed a search, through PubMed, HINARI, Google Scholar, EBSCOhost, and databases. A narrative synthesis through evaluation of vitamin D and LL-37 levels, the association of vitamin D and LL-37, and other variables in individual primary studies were performed. A random-effect model was performed and weighted means were pooled at a 95% confidence interval. This protocol is registered under the International Prospective Register of Systematic Reviews (PROSPERO), registration number CRD42019127232.

RESULTS

Of the 2507 articles selected12 studies were eligible for the systematic review and of these only nine were included in the meta-analysis for vitamin D levels and six for LL-37 levels. Eight studies were performed in Asia, three in Europe, and only one study in Africa. The mean age of the participants was 37.3±9.9 yrs. We found low vitamin D and high cathelicidin levels among the tuberculosis patients compared to non-tuberculosis individuals to non-tuberculosis. A significant difference was observed in both vitamin D and LL-37 levels among tuberculosis patients and non-tuberculosis individuals (p = < 0.001).

CONCLUSION

This study demonstrated that active pulmonary tuberculosis disease is associated with hypovitaminosis D and elevated circulatory cathelicidin levels with low local LL-37 expression. This confirms that vitamin D status has a protective role against tuberculosis disease.

FasL regulatory B-cells during Mycobacterium tuberculosis infection and TB disease

Tuberculosis (TB) disease remains a major health crisis. Infection with Mycobacterium tuberculosis (M.tb) cause a range of diseases ranging from latent infection to active TB disease. This active state of the disease is characterised by the formation of granulomas (a physical barrier in the lung), a structure thought to protect the host by controlling the infection through preventing the growth of the bacilli. Subsequently, the surviving bacteria become inactive and in most cases, TB reactivation is prevented by the immune response of the host. B-cells perform numerous immunological functions beyond antibody production to positively regulate the response to pathogenic assault. A subgroup of B-cells with regulatory functions express death-inducing ligands, such as Fas ligand (FasL). Expression and interaction of the Fas receptor-ligand promotes the induction of apoptosis and the induction of T-cell tolerance. Here, we focus on the significance of B-cells by addressing their FasL phenotype and regulatory functions during TB, with reference to disease in humans, non-human primates and mice.

New insights into regulatory B cells biology in viral, bacterial, and parasitic infections

B lymphocytes are primarily well known for their contribution to immunity by antibody production, antigen presentation and, the production of cytokines. In recent years several studies demonstrated the existence of B cells with regulatory functions, which have been termed regulatory B cells (B_regs), similar to regulatory T cells (T_regs). B_regs are a subpopulation of B cells that have immunosuppressive effects via the production of regulatory cytokines including interleukin-10 (IL-10), transforming growth factor-β (TGF-β), and IL-35. B_regs limit host defense against various pathogens. In addition, B_regs contribute to increased levels of regulatory cytokines and leads to an induction of suppressive T_regs, which exert broader suppressive functions against various pathogens. The high percentage of B_regs is positively associated with viral and bacterial load and can contribute to poor vaccine responses. B_regs can also facilitate pathogen survival at an early stage of infection, and subsequently cause increased severity of disease by inhibiting pro-inflammatory cytokine production, macrophage activation, and inflammatory T cells activation such as Th1, Th17, and Th22. Also, B_regs afford protection against the hyper-inflammatory response in parasitic infections. Here we review the central role of B_regs in many major bacterial and viral human infections, and provide an overview of the immunoregulatory mechanisms used by B_regs.

Slow radiological improvement and persistent low-grade inflammation after chemotherapy in tuberculosis patients with type 2 diabetes

Background

Diabetes mellitus type 2 (DM) may impede immune responses in tuberculosis (TB) and thus contribute to enhanced disease severity. In this study, we aimed to evaluate DM-mediated alterations in clinical, radiological and immunological outcomes in TB disease.

Methods

Newly diagnosed pulmonary TB patients with or without DM (TB n = 40; TB-DM n = 40) were recruited in Dhaka, Bangladesh. Clinical symptoms, sputum smear and culture conversion as well as chest radiography were assessed. Peripheral blood and sputum samples were collected at the time of diagnosis (baseline) and after 1, 2 and 6 months of standard anti-TB treatment. Blood samples were also obtained from healthy controls (n = 20). mRNA expression of inflammatory markers in blood and sputum samples were quantified using real-time PCR.

Results

The majority of TB-DM patients had poor glycemic control (HbA1c > 8%) and displayed elevated pulmonary pathology (P = 0.039) particularly in the middle (P < 0.004) and lower lung zones (P < 0.02) throughout the treatment period. However, reduction of clinical symptoms and time to sputum smear and culture conversion did not differ between the groups. Transcripts levels of the pro-inflammatory cytokines IL-1β (P = 0.003 at month-1 and P = 0.045 at month-2) and TNF-α (P = 0.005 at month-1) and the anti-inflammatory cytokine IL-10 (P = 0.005 at month-2) were higher in peripheral blood after anti-TB treatment in TB-DM compared to TB patients. Conversely in sputum, TB-DM patients had reduced CD4 (P < 0.009 at month-1) and IL-10 (P = 0.005 at month-1 and P = 0.006 at month-2) transcripts, whereas CD8 was elevated (P = 0.016 at month-2). At 1- and 2-month post-treatment, sputum IL-10 transcripts were inversely correlated with fasting blood glucose and HbA1c levels in all patients.

Conclusion

Insufficient up-regulation of IL-10 in the lung may fuel persistent local inflammation thereby promoting lung pathology in TB-DM patients with poorly controlled DM.

A double burden of tuberculosis and diabetes mellitus and the possible role of vitamin D deficiency

Tuberculosis remains a major global health challenge, particularly in low-to-middle income countries such as China. At the same time, the country is facing a rapidly increasing diabetes incidence over the last 10 years. Diabetes aggravates the tuberculosis epidemic which poses a serious challenge in public health. In recent years, the high prevalence of vitamin D deficiency represents a global health problem, which is also associated with the risk of diabetes, and tuberculosis. Therefore, this review aims to provide an overall and updated understanding of the epidemiology of co-occurrence of tuberculosis and diabetes in China, and to elucidate the possible role of vitamin D deficiency. In conclusion, significant aggravation of the tuberculosis epidemic due to diabetes may exist in China for a relatively long period of time to come. Further, the double burden and its implications to public health in this country may be significantly influenced by the high prevalence of vitamin D deficiency. Bidirectional screening for tuberculosis and diabetes is recommended, and extra vitamin D may benefit especially in a situation of a heavy tuberculosis burden combined with prevalent vitamin D deficiency. Longitudinal studies to verify the role of vitamin D deficiency in the double burden, and trials on the effect of vitamin D supplementation are needed in the future.

Methylation Status of VDR Gene and its Association with Vitamin D Status and VDR Gene Expression in Pediatric Tuberculosis Disease

Deficiency in circulatory vitamin D level and vitamin D receptor DNA methylation could be associated with weakened innate immune response and increased susceptibility to tuberculosis (TB) disease in children. Therefore, we aimed to study the effect of vitamin D receptor (VDR) gene methylation on plasma vitamin D level and the expression of the VDR gene in children with active-TB disease. A cross-sectional comparative study was conducted in 43 children with active-TB and 33 healthy control children (HC). The vitamin D level was measured in plasma, while the levels of VDR gene promoter methylation and VDR gene expression were measured in peripheral blood. Children with active-TB showed a significantly lower median vitamin D level than HC [Cases 17.18 ng/mL (IQR, 8.3-18.6 ng/mL); HC 41.34 ng/mL (IQR, 40.2-43.49 ng/mL) (p<0.0001)] and decreased mRNA expression level of VDR gene [Cases 0.51 (IQR, 0.40-0.70); HC 1.06 (IQR, 0.8-1.2) (p<0.0001)] and increased VDR DNA methylation [Cases 75% (IQR, 50-75%); HC 10% (IQR, 10-25%) (p<0.0001)]. The VDR hypermethylation is significantly associated with reduced vitamin D level and decreased expression level of VDR gene. Therefore this inverse association could be involved in the impairment in the VDR mediated cytolytic and antimicrobial effector cell response in pediatric TB disease.

Acute hypercalcemia and hypervitaminosis D associated with pulmonary tuberculosis in an elderly patient : A case report and review of the literature

An 80-year-old man was referred to our hospital for further examination of fever, cough and left pleural effusion. The laboratory findings showed acute inflammation, and the elevation of albumin-corrected serum calcium and 1,25-dihydroxyvitamin D3. A chest CT revealed centrilobular particulate opacity in the bilateral lung fields and left pleural effusion, indicating acute hypercalcemia and hypervitaminosis D associated with pulmonary tuberculosis. By the confirmation of Mycobacterium tuberculosis on polymerase chain reaction and cultures of the sputum and pleural effusion, a diagnosis of pulmonary tuberculosis was made. The patient successfully completed a 9-month course of the anti-tuberculosis treatment, and bilateral infiltrative shadows and left pleural effusion in chest X-ray disappeared. Symptoms progressively improved and serum level of albumin-corrected calcium and 1,25-dihydroxyvitamin D3 eventually normalized. While pulmonary tuberculosis is an infrequent cause of hypercalcemia, it should be considered in patients with hypercalcemia and elevated serum level of 1,25-dihydroxyvitamin D3. J. Med. Invest. 66 : 351-354, August, 2019.

Vitamin D-Cathelicidin Axis: at the Crossroads between Protective Immunity and Pathological Inflammation during Infection

Vitamin D signaling plays an essential role in innate defense against intracellular microorganisms via the generation of the antimicrobial protein cathelicidin. In addition to directly binding to and killing a range of pathogens, cathelicidin acts as a secondary messenger driving vitamin D-mediated inflammation during infection. Recent studies have elucidated the biological and clinical functions of cathelicidin in the context of vitamin D signaling. The vitamin D-cathelicidin axis is involved in the activation of autophagy, which enhances antimicrobial effects against diverse pathogens. Vitamin D studies have also revealed positive and negative regulatory effects of cathelicidin on inflammatory responses to pathogenic stimuli. Diverse innate and adaptive immune signals crosstalk with functional vitamin D receptor signals to enhance the role of cathelicidin action in cell-autonomous effector systems. In this review, we discuss recent findings that demonstrate how the vitamin D-cathelicidin pathway regulates autophagy machinery, protective immune defenses, and inflammation, and contributes to immune cooperation between innate and adaptive immunity. Understanding how the vitamin D-cathelicidin axis operates in the host response to infection will create opportunities for the development of new therapeutic approaches against a variety of infectious diseases.

Polarization of Human Monocyte-Derived Cells With Vitamin D Promotes Control of Mycobacterium tuberculosis Infection

Background: Understanding macrophage behavior is key to decipher Mycobacterium tuberculosis (Mtb) pathogenesis. We studied the phenotype and ability of human monocyte-derived cells polarized with active vitamin D [1,25(OH)₂D₃] to control intracellular Mtb infection compared with polarization of conventional subsets, classical M1 or alternative M2.

Methods: Human blood-derived monocytes were treated with active vitamin D or different cytokines to obtain 1,25(OH)₂D₃-polarized as well as M1- and M2-like cells or fully polarized M1 and M2 subsets. We used an in vitro macrophage Mtb infection model to assess both phenotype and functional markers i.e., inhibitory and scavenger receptors, costimulatory molecules, cytokines, chemokines, and effector molecules using flow cytometry and quantitative mRNA analysis. Intracellular uptake of bacilli and Mtb growth was monitored using flow cytometry and colony forming units.

Results: Uninfected M1 subsets typically expressed higher levels of CCR7, TLR2, and CD86, while M2 subsets expressed higher CD163, CD200R, and CD206. Most of the investigated markers were up-regulated in all subsets after Mtb infection, generating a mixed M1/M2 phenotype, while the expression of CD206, HLADR, and CD80 was specifically up-regulated (P < 0.05) on 1,25(OH)₂D₃-polarized macrophages. Consistent with the pro-inflammatory features of M1 cells, Mtb uptake and intracellular Mtb growth was significantly (P < 0.01–0.001 and P < 0.05–0.01) lower in the M1 (19.3%) compared with the M2 (82.7%) subsets 4 h post-infection. However, infectivity rapidly and gradually increased in M1 cells at 24–72 h. 1,25(OH)₂D₃-polarized monocyte-derived cells was the most potent subset to inhibit Mtb growth at both 4 and 72 h (P < 0.05–0.01) post-Mtb infection. This ability was associated with high mRNA levels of pro-inflammatory cytokines and the antimicrobial peptide LL-37 but also anti-inflammatory IL-10, while expression of the immunosuppressive enzyme IDO (indoleamine 2,3-dioxygenase) remained low in Mtb-infected 1,25(OH)₂D₃-polarized cells compared with the other subsets.

Conclusions: Mtb infection promoted a mixed M1/M2 macrophage activation, and 1,25(OH)₂D₃-polarized monocyte-derived cells expressing LL-37 but not IDO, were most effective to control intracellular Mtb growth. Macrophage polarization in the presence of vitamin D may provide the capacity to mount an antimicrobial response against Mtb and simultaneously prevent expression of inhibitory molecules that could accelerate local immunosuppression in the microenvironment of infected tissue.

Host-Directed Therapy as a Novel Treatment Strategy to Overcome Tuberculosis: Targeting Immune Modulation

Tuberculosis (TB) is one of the leading causes of mortality and morbidity, particularly in developing countries, presenting a major threat to the public health. The currently recommended long term treatment regimen with multiple antibiotics is associated with poor patient compliance, which in turn, may contribute to the emergence of multi-drug resistant TB (MDR-TB). The low global treatment efficacy of MDR-TB has highlighted the necessity to develop novel treatment options. Host-directed therapy (HDT) together with current standard anti-TB treatments, has gained considerable interest, as HDT targets novel host immune mechanisms. These immune mechanisms would otherwise bypass the antibiotic bactericidal targets to kill Mycobacterium tuberculosis (Mtb), which may be mutated to cause antibiotic resistance. Additionally, host-directed therapies against TB have been shown to be associated with reduced lung pathology and improved disease outcome, most likely via the modulation of host immune responses. This review will provide an update of host-directed therapies and their mechanism(s) of action against Mycobacterium tuberculosis.

Host-Targeted Therapeutics against Multidrug Resistant Intracellular Staphylococcus aureus

Staphylococcus aureus is a facultative intracellular pathogen that invades and replicates within many types of human cells. S. aureus has shown to rapidly overcome traditional antibiotherapy by developing multidrug resistance. Furthermore, intracellular S. aureus is protected from the last-resort antibiotics—vancomycin, daptomycin, and linezolid—as they are unable to achieve plasma concentrations sufficient for intracellular killing. Therefore, there is an urgent need to develop novel anti-infective therapies against S. aureus infections. Here, we review the current state of the field and highlight the exploitation of host-directed approaches as a promising strategy going forward.

The Humoral Immune Response to BCG Vaccination

Bacillus Calmette Guérin (BCG) is the only currently available vaccine against tuberculosis (TB), but it confers incomplete and variable protection against pulmonary TB in humans and bovine TB (bTB) in cattle. Insights into the immune response induced by BCG offer an underexploited opportunity to gain knowledge that may inform the design of a more efficacious vaccine, which is urgently needed to control these major global epidemics. Humoral immunity in TB and bTB has been neglected, but recent studies supporting a role for antibodies in protection against TB has driven a growing interest in determining their relevance to vaccine development. In this manuscript we review what is known about the humoral immune response to BCG vaccination and re-vaccination across species, including evidence for the induction of specific B cells and antibodies; and how these may relate to protection from TB or bTB. We discuss potential explanations for often conflicting findings and consider how factors such as BCG strain, manufacturing methodology and route of administration influence the humoral response. As novel vaccination strategies include BCG prime-boost regimens, the literature regarding off-target immunomodulatory effects of BCG vaccination on non-specific humoral immunity is also reviewed. Overall, reported outcomes to date are inconsistent, but indicate that humoral responses are heterogeneous and may play different roles in different species, populations, or individual hosts. Further study is warranted to determine whether a new TB vaccine could benefit from the targeting of humoral as well as cell-mediated immunity.

Bcells and their regulatory functions during Tuberculosis: Latency and active disease

Tuberculosis (TB) is a global epidemic with devastating consequences. Emerging evidence suggests that B-cells have the ability to modulate the immune response and understanding these roles during Mycobacterium tuberculosis (M.tb) infection can help to find new strategies to treat TB. The immune system of individuals with pulmonary TB form granulomas in the lung which controls the infection by inhibiting the M.tb growth and acts as a physical barrier. Thereafter, surviving M.tb become dormant and in most cases the host's immunity prevents TB reactivation. B-cells execute several immunological functions and are regarded as protective regulators of immune responses by antibody and cytokine production, as well as presenting antigen. Some of these B-cells, or regulatory B-cells, have been shown to express death-inducing ligands, such as Fas ligand (FasL). This expression and binding to the Fas receptor leads to apoptosis, a major immune regulation mechanism, in addition to the ability to induce T-cell tolerance. Here, I discuss the relevance of B-cells, in particular their non-humoral functions by addressing their regulatory properties during M.tb infection.

The lung microbiome, vitamin D, and the tuberculous granuloma: A balance triangle

Mycobacterium tuberculosis (Mtb) has the extraordinary ability to persist for decades within granulomas in the human host. These histopathological structures involved in both protection and pathogenesis, are subject to various influences from the host systemically and through micro-niche environments. Despite the fact that vitamin D (VD) has a key role in macrophage activation and mycobacterial clearance in the early stages of Mtb infection, the overall role of VD in granuloma maintenance or functionality has been scarcely studied. VD deficiency has long time been known to influence on gut microbiota composition, and recent studies have shown that it can also impact on respiratory microbiome. The human microbiota plays an important role in pathogen colonization resistance, and it has been proposed to play a potential role in TB pathogenesis. In this article, we have reviewed current knowledge on the interaction between VD, the lung microbiome and TB, and propose mechanisms by which the tuberculous granuloma's outcome could be modulated by these two factors. The determinants of the final fate of lung granulomas are still unclear, and deciphering the underlying drivers of Mtb infection outcome within those structures is of critical importance.

An Observational Case-Control Study to Determine Human Immunodeficiency Virus and Host Factor Influence on Biomarker Distribution and Serodiagnostic Potential in Adult Pulmonary Tuberculosis

Influence of host factors, including human immunodeficiency virus (HIV) co-infection, on the distribution and diagnostic potential of previously evaluated biomarkers of pulmonary tuberculosis (PTB), such as anti-antigen 60 (A60) immunoglobulin (Ig) G, anti-A60 IgA, and C-reactive protein (CRP), remain unclear. Anti-A60 IgG, anti-A60 IgA, and CRP in PTB and non-PTB patient sera (n = 404, including smear-positive/negative, culture-positive (SPCP/SNCP) and HIV+ve/-ve) were measured by enzyme-linked immunoassay and statistically analysed. In multinomial logistic regression, expectoration, chest pain, wasting, and culture count positively associated with CRP (p < 0.001), while smear count positively associated with anti-A60 IgG (p = 0.090). Expectoration and enlarged lymph nodes negatively associated with anti-A60 IgA (p = 0.018). Biomarker distribution and diagnostic potential varied significantly by symptoms and bacilli burden, and across different PTB subpopulations. CRP was correlated poorly with anti-A60 antibodies, while anti-A60 IgA and IgG were correlated in non-tuberculosis (TB) and SPCP patients (p < 0.001). When combined, anti-A60 IgG and CRP best discriminated SPCP/HIV-ve from non-TB (AUC: 0.838, 95% CI: 0.783⁻0.894), while anti-A60 IgA and CRP performed best in discriminating HIV+ve PTB from non-TB (AUC: 0.687, 95% CI: 0.598⁻0.777). Combined CRP and anti-A60 antibodies had significantly reduced accuracy in SNCP and SNCP/HIV+ve compared to SPCP/HIV-ve subpopulations. The complex relationships between host factors and biomarkers suggest their limited utility, especially in SNCP/HIV+ve subpopulations, highlighting the importance of examining host response and immune biomarkers across relevant patient subpopulations.

Study of IL-6 and vitamin D3 in patients of pulmonary tuberculosis

BACKGROUND

Mycobacterium tuberculosis can grow in hostile intracellular environment of macrophages by actively evading macrophage-associated antibacterial activities. The stress response factor contributes this process by releasing inflammatory cytokine Interleukin 6 (IL-6). IL-6 screening of patients with TB may be useful to monitor the progress of infection and to infer the risk of progression to active disease. Vitamin D has a critical role in the innate immune system, in the circulating metabolite and supports induction of pleiotropic antimicrobial responses, through the production of antimicrobial peptides, particularly cathelicidin and its active metabolite. 1,25-dihydoxyvitamin D, has long been known to enhance immune response to mycobacteria. In this study, we have studied the role of IL-6 and Vitamin D3 in M. tuberculosis.

MATERIALS AND METHODS

Three groups involved in this study are Control, Category I (newly diagnosed TB) and MDR TB patients. The serum levels of IL-6 and vitamin D3 were measured using chemiluminescence and fully-automated enzyme-linked immunosorbent assay respectively.

RESULTS

The serum levels of IL-6 were significantly increased, whereas vitamin D3 decreased in TB multidrug-resistant group of patients compared to the newly diagnosed TB patients.

CONCLUSION

IL-6 appears to be the major cytokine elaborated by mycobacteria infection as well as play a role in the clinical manifestations and pathological events and hence may function as a potent biomarker of tuberculosis. Since, Vitamin D increases activity of cell-mediated immunity; it can be used as a supplementation during tuberculosis therapy.

Vitamin D₃ Status and the Association with Human Cathelicidin Expression in Patients with Different Clinical Forms of Active Tuberculosis

Low vitamin D (vitD₃) is one of the most common nutritional deficiencies in the world known to be associated with numerous medical conditions including infections such as tuberculosis (TB). In this study, vitD₃ status and its association with the antimicrobial peptide, human cathelicidin (LL-37), was investigated in Ethiopian patients with different clinical forms of TB. Patients with active TB (n = 77) and non-TB controls (n = 78) were enrolled in Ethiopia, while another group of non-TB controls (n = 62) was from Sweden. Active TB included pulmonary TB (n = 32), pleural TB (n = 20), and lymph node TB (n = 25). Concentrations of 25-hydroxyvitamin D₃ (25(OH)D₃) were assessed in plasma, while LL-37 mRNA was measured in peripheral blood and in samples obtained from the site of infection. Median 25(OH)D₃ plasma levels in active TB patients were similar to Ethiopian non-TB controls (38.5 versus 35.0 nmol/L) and vitD₃ deficiency (.

Vitamin D and tuberculosis: where next?

Tuberculosis (TB) has troubled mankind for millennia, but current treatment strategies are long and complicated and the disease remains a major global health problem. The risk of Mycobacterium tuberculosis (Mtb) infection or progression of active TB disease is elevated in individuals with vitamin D deficiency. High-dose vitamin D was used to treat TB in the preantibiotic era, and in vitro experimental data show that vitamin D supports innate immune responses that restrict growth of Mtb. Several randomized controlled trials have tested whether adjunctive vitamin D supplementation enhances the clinical and microbiological response to standard antimicrobial chemotherapy for pulmonary TB. The effects have been modest at best, and attention is turning to the question of whether vitamin D supplementation might have a role in preventing acquisition or reactivation of latent Mtb infection. In this article, we describe the effects of vitamin D on host immune responses to Mtb in vitro and in vivo and review the results of clinical trials in the field. We also reflect on the findings of clinical trials of vitamin D supplementation for the prevention of acute respiratory tract infections, and discuss how these findings might influence the design of future trials to evaluate the role of vitamin D in the prevention and treatment of TB.

Prospective study of immunomodulation in osteoarticular tuberculosis non responsive to anti tubercular therapy

BACKGROUND

Tuberculosis is one of the common disease of Indian subcontinent. India has the highest TB burden, accounting for one fifth of the global incidence. Previous studies have shown positive response of immunomodulation in patients of ostearticular tuberculosis We did this prospective study to assess the role of immunomodulation in the cases of osteoarticular tuberculosis who were not responding to anti tubercular therapy.

MATERIALS AND METHOD

This study was conducted in our institute. New patients presenting to OPD who were diagnosed with tuberculosis with no previous history of taking anti tubercular treatment were enrolled. Total of 109 patients were diagnosed clinicoradiologically. Four patients, where diagnosis was not confirmed, histopathological examination of tissue was done and the diagnosis was confirmed as tubercular in origin. Newly diagnosed patients were put on anti tubercular therapy(ATT) after documenting there blood parameters (complete hemogram,ESR, serum proteins, CD4 & CD8 counts). After 3 months patients were re-evaluated and favourably responding patients were labelled group A. Those who did not respond to therapy were put on immunomodulation along with continuation of ATT. These were designated as group B and blood parameters were compared with pre immunomodulation values.

RESULTS

Out of total 109 patients registered, 73 patients were enlisted in group A, while 30 patients were found to be non-responsive to ATT and were included in non-responder group B (six lost to follow up). In group B the blood parameters after one month of completion of immunomodulation showed statistically significant increase in CD4 & CD8 counts (p = 0.04). Mean CD4 count increased from 488/mm³ to 747/mm³ while CD8 count showed increment from 494/mm³ to 617/mm³. Mean haemoglobin values increased along with decrease in ESR and total leucocyte count. In group A mean CD4 and CD8 counts increased with ATT though the results were not significant statistically.

CONCLUSION

Treatment: of tuberculosis has been a great success after introduction of chemotherapy specifically targeting Mycobacterium tuberculosis. In this study relationship between the increase in the peripheral T-cell count and a favourable clinical outcome was further associated with concomitant increase in the haemoglobin level as well as by a decrease in the ESR, total leucocyte count. In our study immunomodulation has shown a good promise to be of adjunctive use in patients on ATT with non-responsiveness.

The Troika Host-Pathogen-Extrinsic Factors in Tuberculosis: Modulating Inflammation and Clinical Outcomes

The already enormous burden caused by tuberculosis (TB) will be further aggravated by the association of this disease with modern epidemics, as human immunodeficiency virus and diabetes. Furthermore, the increasingly aging population and the wider use of suppressive immune therapies hold the potential to enhance the incidence of TB. New preventive and therapeutic strategies based on recent advances on our understanding of TB are thus needed. In particular, understanding the intricate network of events modulating inflammation in TB will help to build more effective vaccines and host-directed therapies to stop TB. This review integrates the impact of host, pathogen, and extrinsic factors on inflammation and the almost scientifically unexplored complexity emerging from the interactions between these three factors. We highlight the exciting data showing a contribution of this troika for the clinical outcome of TB and the need of incorporating it when developing novel strategies to rewire the immune response in TB.

Serum Vitamin D Level as a Risk Factor for Female Genital Tuberculosis (FGTB)

Introduction

Vitamin D is now known to be essential to Mycobacterium tuberculosis containment and killing through activation of 25-hydroxyvitamin-D receptors (VDRs) present on all immune cells or obtained from dietary food stuffs as either vitamin D3 or vegetable vitamin D2 (also known as ergocalciferol).

Aim

To evaluate the association of serum vitamin D level between the Female Genital Tuberculosis (FGTB) cases and healthy controls.

Materials and Methods

Total 120 cases and 120 controls enrolled for the study following inclusion and exclusion criteria. Detailed clinical history was taken from each subjects. Total of 3 ml of the blood was collected in EDTA vial from each subject (case and control). Quantification of serum vitamin D level was measured by active human vitamin D ELISA kit using an ELISA reader. Statistical analysis was done using Statistical Package for Social Science (SPSS) version 21.0. A p-value <0.05 was considered as significant.

Results

A total of 120 confirmed FGTB cases and 120 healthy control enrolled for study. Out of 120 women 97.5%, 10.0%, 3.3%, 3.3% were detected positive for M. tuberculosis respectively. Comparing the mean demographic value of age and BMI were (29.03±3.127, 28.03±3.00) and (22.92±3.33, 24.15±3.97) respectively with the p=0.012* and p=0.010* found to be significant among cases and controls. The mean serum vitamin D level was 14.96±8.81 in cases and 23.00±8.83 in controls with p-value<0.001. There was a significant positive association found in low serum vitamin D level among FGTB cases than controls.

Conclusion

Vitamin D is important for normal immune cell function, as well as regression of FGTB disease. FGTB may be controlled by regulating the serum vitamin D level concentration. This study suggests that, vitamin D deficiency and BMI is strongly associated with the progression of active FGTB disease which alters the expression of antimicrobial peptide and lead to the persistence of TB infection. Therefore, serum vitamin D level may play an important role in treatment of FGTB.

Inhibition of Tissue Matrix Metalloproteinases Interferes with Mycobacterium tuberculosis-Induced Granuloma Formation and Reduces Bacterial Load in a Human Lung Tissue Model

Granulomas are hallmarks of pulmonary tuberculosis (TB) and traditionally viewed as host-protective structures. However, recent evidence suggest that Mycobacterium tuberculosis (Mtb) uses its virulence factors to stimulate the formation of granuloma. In the present study, we investigated the contribution of matrix metalloproteinases (MMPs), host enzymes that cause degradation of the extracellular matrix, to granuloma formation and bacterial load in Mtb-infected tissue. To this end, we used our lung tissue model for TB, which is based on human lung-derived cells and primary human monocyte-derived macrophages. Global inhibition of MMPs in the Mtb-infected tissue model reduced both granuloma formation and bacterial load. The infection caused upregulation of a set of MMPs (MMP1, 3, 9, and 12), and this finding could be validated in lung biopsies from patients with non-cavitary TB. Data from this study indicate that MMP activation contributes to early TB granuloma formation, suggesting that host-directed, MMP-targeted intervention could be considered as adjunct therapy to TB treatment.

Regulation of Immune Function by Vitamin D and Its Use in Diseases of Immunity

Evidence exists for a role for vitamin D and its active metabolites in modulating immune functions. In animal models, vitamin D deficiency is associated with a higher risk for autoimmunity in genetically predisposed subjects and increases in susceptibility to infections. In addition, high-dose vitamin D can improve immune health, prevent autoimmunity, and improve defense against infections. In humans, evidence exists on associations between vitamin D deficiency and impaired immune function, leading to autoimmunity in genetically predisposed people and increased risk for infections; data on therapeutic immune effects of vitamin D supplementation when vitamin D levels are already sufficient are lacking.

Mechanisms of Action of Vitamin D as Supplemental Therapy for Pneumocystis Pneumonia

The combination of trimethoprim and sulfamethoxazole (TMP-SMX) is the most effective regimen for therapy of Pneumocystis pneumonia (PCP). As many patients with PCP are allergic or do not respond to it, efforts have been devoted to develop alternative therapies for PCP. We have found that the combination of vitamin D₃ (VitD3) (300 IU/kg/day) and primaquine (PMQ) (5 mg/kg/day) was as effective as TMP-SMX for therapy of PCP. In this study, we investigated the mechanisms by which vitamin D enhances the efficacy of PMQ. C57BL/6 mice were immunosuppressed by CD4⁺ cell depletion, infected with Pneumocystismurina for 8 weeks, and then treated for 9 days with the combination of VitD3 and PMQ (VitD3-PMQ) or with TMP-SMX or PMQ to serve as controls. The results showed that vitamin D supplementation increased the number of CD11c⁺ cells, suppressed the production of proinflammatory cytokines (tumor necrosis factor alpha [TNF-α], gamma interferon [IFN-γ], and interleukin-6 [IL-6]) and inducible nitric oxide synthase (iNOS), and enhanced the expression of genes related to antioxidation (glutathione reductase and glutamate-cysteine ligase modifier subunit), antimicrobial peptides (cathelicidin), and autophagy (ATG5 and beclin-1). These results suggest that the main action of vitamin D is enhancing the ability of the host to defend against Pneumocystis infection.

Regulation of Immunity to Tuberculosis

Immunity against Mycobacterium tuberculosis requires a balance between adaptive immune responses to constrain bacterial replication and the prevention of potentially damaging immune activation. Regulatory T (Treg) cells express the transcription factor Foxp3+ and constitute an essential counterbalance of inflammatory Th1 responses and are required to maintain immune homeostasis. The first reports describing the presence of Foxp3-expressing CD4+ Treg cells in tuberculosis (TB) emerged in 2006. Different Treg cell subsets, most likely specialized for different tissues and microenvironments, have been shown to expand in both human TB and animal models of TB. Recently, additional functional roles for Treg cells have been demonstrated during different stages and spectrums of TB disease. Foxp3+ regulatory cells can quickly expand during early infection and impede the onset of cellular immunity and persist during chronic TB infection. Increased frequencies of Treg cells have been associated with a detrimental outcome of active TB, and may be dependent on the M. tuberculosis strain, animal model, local environment, and the stage of infection. Some investigations also suggest that Treg cells are required together with effector T cell responses to obtain reduced pathology and sterilizing immunity. In this review, we will first provide an overview of the regulatory cells and mechanisms that control immune homeostasis. Then, we will review what is known about the phenotype and function of Treg cells from studies in human TB and experimental animal models of TB. We will discuss the potential role of Treg cells in the progression of TB disease and the relevance of this knowledge for future efforts to prevent, modulate, and treat TB.

Vitamin D Counteracts Mycobacterium tuberculosis-Induced Cathelicidin Downregulation in Dendritic Cells and Allows Th1 Differentiation and IFNγ Secretion

Tuberculosis (TB) presents a serious health problem with approximately one-third of the world's population infected with Mycobacterium tuberculosis in a latent state. Experience from the pre-antibiotic era and more recent clinical studies have established a beneficial role of sunlight and vitamin D in patients with TB. At the same time, experimental data have shown that Th1 cells through production of IFNγ are crucial for cathelicidin release by macrophages, bacterial killing, and containment of M. tuberculosis in granulomas. Paradoxically, vitamin D has repeatedly been ascribed an immune-suppressive function inhibiting Th1 differentiation and production of IFNγ in T cells. The aim of this study was to investigate this apparent paradox. We studied naïve human CD4⁺ T cells activated either with CD3 and CD28 antibodies or with allogeneic dendritic cells (DC) stimulated with heat-killed M. tuberculosis (HKMT) or purified toll-like receptor (TLR) ligands. We show that vitamin D does not block differentiation of human CD4⁺ T cells to Th1 cells and that interleukin (IL)-12 partially counteracts vitamin D-mediated inhibition of IFNγ production promoting production of equal amounts of IFNγ in Th1 cells in the presence of vitamin D as in T cells activated in the absence of vitamin D and IL-12. Furthermore, we show that HKMT and TLR2 ligands strongly downregulate cathelicidin expression in DC and that vitamin D counteracts this by upregulating cathelicidin expression. In conclusion, we demonstrate that vitamin D counteracts M. tuberculosis-induced cathelicidin downregulation and allows Th1 differentiation and IFNγ secretion.

IL-21 signaling is essential for optimal host resistance against Mycobacterium tuberculosis infection

IL-21 is produced predominantly by activated CD4⁺ T cells and has pleiotropic effects on immunity via the IL-21 receptor (IL-21R), a member of the common gamma chain (γ_c) cytokine receptor family. We show that IL-21 signaling plays a crucial role in T cell responses during Mycobacterium tuberculosis infection by augmenting CD8⁺ T cell priming, promoting T cell accumulation in the lungs, and enhancing T cell cytokine production. In the absence of IL-21 signaling, more CD4⁺ and CD8⁺ T cells in chronically infected mice express the T cell inhibitory molecules PD-1 and TIM-3. We correlate these immune alterations with increased susceptibility of IL-21R^−/− mice, which have increased lung bacterial burden and earlier mortality compared to WT mice. Finally, to causally link the immune defects with host susceptibility, we use an adoptive transfer model to show that IL-21R^−/− T cells transfer less protection than WT T cells. These results prove that IL-21 signaling has an intrinsic role in promoting the protective capacity of T cells. Thus, the net effect of IL-21 signaling is to enhance host resistance to M. tuberculosis. These data position IL-21 as a candidate biomarker of resistance to tuberculosis.

Host-directed therapies for infectious diseases: current status, recent progress, and future prospects

Despite extensive global efforts in the fight against killer infectious diseases, they still cause one in four deaths worldwide and are important causes of long-term functional disability arising from tissue damage. The continuing epidemics of tuberculosis, HIV, malaria, and influenza, and the emergence of novel zoonotic pathogens represent major clinical management challenges worldwide. Newer approaches to improving treatment outcomes are needed to reduce the high morbidity and mortality caused by infectious diseases. Recent insights into pathogen–host interactions, pathogenesis, inflammatory pathways, and the host's innate and acquired immune responses are leading to identification and development of a wide range of host-directed therapies with different mechanisms of action. Host-directed therapeutic strategies are now becoming viable adjuncts to standard antimicrobial treatment. Host-directed therapies include commonly used drugs for non-communicable diseases with good safety profiles, immunomodulatory agents, biologics (eg monoclonal antibodies), nutritional products, and cellular therapy using the patient's own immune or bone marrow mesenchymal stromal cells. We discuss clinically relevant examples of progress in identifying host-directed therapies as adjunct treatment options for bacterial, viral, and parasitic infectious diseases.

B in TB: B Cells as Mediators of Clinically Relevant Immune Responses in Tuberculosis

The protective role of B cells and humoral immune responses in tuberculosis infection has been regarded as inferior to cellular immunity directed to the intracellular pathogen Mycobacterium tuberculosis. However, B-cell–mediated immune responses in tuberculosis have recently been revisited in the context of B-cell physiology and antigen presentation. We discuss in this review the diverse functions of B cells in tuberculosis, with a focus on their biological and clinical relevance to progression of active disease. We also present the peptide microarray platform as a promising strategy to discover unknown antigenic targets of M. tuberculosis that could contribute to the better understanding of epitope focus of the humoral immune system against M. tuberculosis.

Potential of immunomodulatory agents as adjunct host-directed therapies for multidrug-resistant tuberculosis

Treatment of multidrug-resistant tuberculosis (MDR-TB) is extremely challenging due to the virulence of the etiologic strains of Mycobacterium tuberculosis (M. tb), the aberrant host immune responses and the diminishing treatment options with TB drugs. New treatment regimens incorporating therapeutics targeting both M. tb and host factors are urgently needed to improve the clinical management outcomes of MDR-TB. Host-directed therapies (HDT) could avert destructive tuberculous lung pathology, facilitate eradication of M. tb, improve survival and prevent long-term functional disability. In this review we (1) discuss the use of HDT for cancer and other infections, drawing parallels and the precedent they set for MDR-TB treatment, (2) highlight preclinical studies of pharmacological agents commonly used in clinical practice which have HDT potential, and (3) outline developments in cellular therapy to promote clinically beneficial immunomodulation to improve treatment outcomes in patients with pulmonary MDR-TB. The use of HDTs as adjuncts to MDR-TB therapy requires urgent evaluation.

LL-37: Cathelicidin-related antimicrobial peptide with pleiotropic activity

Antimicrobial peptides (AMPs) is a large family of compounds serving as natural antibiotics, widely distributed across the organism, mainly in mucus layers. They are designed to prevent pathogens from colonization. Among them, defensins and cathelicidins could be found. LL-37, the sole human cathelicidin draws particular attention because of its outstanding abilities. In addition to being a broad spectrum antibiotic, LL-37 has potent chemotactic and immunomodulatory properties. In this review, we discussed the potency of LL-37 as a therapeutic agent in four systems: immunological, respiratory, gastrointestinal and in the skin. We analyzed the main molecular pathways dependent on human cathelicidin and related them to specific diseases. We conclude that LL-37 shows a great potential to be further investigated and developed as a drug with clinical use.

Interaction between antimicrobial peptides and mycobacteria

Mycobacteria can cause different severe health problems, including tuberculosis (TB). The treatment of TB with conventional antibiotics is successful, however, the number of multi-drug and extensively-drug resistant Mycobacterium tuberculosis strains increases. Moreover, many classical antimycobacterial antibiotics have severe side effects. Therefore, antimicrobial peptides (AMPs) seem to be good candidates for new therapeutic strategies. On the one hand AMPs can be used as a single drug or in combination with conventional antibiotics to directly kill mycobacteria, or on the other hand to act as immunstimulatory agents. This review summarizes the findings on the role of endogenous human AMPs being involved in TB, the antimycobacterial activity of various AMPs, and the molecular modes of action. Most active AMPs interact with the mycobacterial cell envelope and in particular with the mycomembrane and the plasma membrane. The mycomembrane is a very rigid membrane probably leading to a lower activity of the AMPs against mycobacteria as compared to other Gram-negative or Gram-positive bacteria. For some AMPs also other targets have been identified. Because of the complex environment of intracellular mycobacteria being trapped in the phagosome, within the macrophage, within the granuloma, within the lung, the external administration of AMPs in the latent phase of TB is a challenge. However, in the acute phase the AMPs can attack mycobacteria in a direct way. This article is part of a Special Issue entitled: Antimicrobial peptides edited by Karl Lohner and Kai Hilpert.

Enhanced LL-37 expression following vitamin D supplementation in patients with cirrhosis and spontaneous bacterial peritonitis

BACKGROUND & AIMS

The morbidity and mortality of spontaneous bacterial peritonitis (SBP) are high among patients with cirrhosis; however, the mechanisms of SBP pathogenesis are poorly understood. This study aimed to determine the role of the vitamin D-LL-37 pathway in the pathogenesis and treatment in patients with cirrhosis and SBP.

METHODS

Serum 25-hydroxyvitamin D concentrations of 119 patients with chronic liver diseases were tested. Vitamin D receptor (VDR) and LL-37 in peritoneal leucocytes of cirrhotic and ascitic patients with SBP were detected and compared with those without SBP. Then the peritoneal macrophages of non-infected patients were cultured and activated by lipopolysaccharide (LPS) to analyse the changes of VDR and LL-37 expressions after incubation with vitamin D.

RESULTS

Vitamin D deficiency or insufficiency was found in all of patients with cirrhosis. LPS inhibited VDR and LL-37 expression in peritoneal macrophages [1.3-fold decrease (P = 0.003) and 20-fold decrease (P = 0.010) respectively]. However, vitamin D could reverse the inhibition of both VDR and LL-37 [1.5-fold increase (P = 0.001) and 2000-fold increase (P < 0.001) respectively]. The effect of the incubation time following vitamin D supplementation was significant for LL-37 expression, with a peak expression found at 36 h (P < 0.001).

CONCLUSIONS

When vitamin D levels were low, bacteria inhibited VDR and LL-37 responses in peritoneal macrophages as a mechanism to evade antibacterial defence. Vitamin D supplementation could up-regulate peritoneal macrophage VDR and LL-37 expressions, which resulted in an enhanced immunological defence against SBP in patients with cirrhosis and ascites.

Hypercalcaemic crisis in an elderly patient with pulmonary tuberculosis

Tuberculosis is an uncommon but recognized cause of hypercalcaemia, though calcium levels are seldom severely elevated and rarely result in symptoms. In the elderly patient however, several competing aetiologies may contribute to hypercalcaemia and the diagnostic evaluation may be confounded by polypharmacy as well as multiple co-existing medical conditions. We present here a case of an elderly man who presented with pulmonary tuberculosis and concomitant delirium secondary to hypercalcaemic crisis. Treatment with anti-tuberculous drugs, together with supportive care, eventually led to resolution of hypercalcaemia and restoration of mental function.

Short, Synthetic Cationic Peptides Have Antibacterial Activity against Mycobacterium smegmatis by Forming Pores in Membrane and Synergizing with Antibiotics

Multicellular organisms are constantly exposed to a multitude of pathogenic microbes. Infection is inhibited in vivo by the innate and adaptive immune system. Mycobacterium species have emerged that are resistant to most antibiotics. We identified several naturally occurring cationic antimicrobial peptides that were active at low micromolar concentrations against Mycobacterium smegmatis. Human-derived cathelicidin LL-37 is well characterized and studied against M. smegmatis; we compared LL-37 with Chinese cobra-derived cathelicidin NA-CATH and mouse cathelicidin (mCRAMP). Two synthetic 11-residue peptides (ATRA-1A and ATRA-2) containing variations of a repeated motif within NA-CATH were tested for their activity against M. smegmatis along with a short synthetic peptide derivative from the human beta-defensin hBD3 (hBD3-Pep4). We hypothesized that these smaller synthetic peptides may demonstrate antimicrobial effectiveness with shorter length (and at less cost), making them strong potential candidates for development into broad-spectrum antimicrobial compounds or use in combination with antibiotics. These peptides have antimicrobial activity with EC50 ranging from 0.05 to 1.88 μg/mL against Mycobacterium smegmatis. The ATRA-1A short peptide was found to be the most effective antimicrobial peptide (AMP) (EC50 = 0.05 μg/mL). High bactericidal activity correlated with bacterial membrane depolarization and permeabilization activities. The efficacy of the peptides was further analyzed through Minimal Inhibitory Concentration (MIC) assays. The MICs were determined by the microdilution method. The peptide mCRAMP showed the best MIC activity at 15.6 μg/mL. Neither of the effective short synthetic peptides demonstrated synergy with the antibiotic rifampicin, although both demonstrated synergy with the cyclic peptide antibiotic polymyxin B. The peptides LL-37 and mCRAMP displayed synergism with rifampicin in MIC assays, whereas antibiotic polymyxin B displayed synergism with LL-37, ATRA-1A, and hBD3-Pep4. In further studies, polymyxin B synergized with LL-37, ATRA-1A, and hBD3-Pep4 while Rifampicin synergized with LL-37 and mCRAMP for intracellular killing of mycobacteria residing inside macrophages. These studies provide the foundation for the potential development of synthetic cationic antimicrobial peptides with activity against mycobacteria.