Pathological role of interleukin 17 in mice subjected to repeated BCG vaccination after infection with Mycobacterium tuberculosis

IL-17RA in Non-Hematopoietic Cells Controls CXCL-1 and 5 Critical to Recruit Neutrophils to the Lung of Mycobacteria-Infected Mice during the Adaptive Immune Response

During chronic infection with Mycobacterium tuberculosis (Mtb), bacilli multiplication is constrained within lung granulomas until excessive inflammation destroys the lung. Neutrophils are recruited early and participate in granuloma formation, but excessive neutrophilia exacerbates the tuberculosis disease. Neutrophils thus appear as potential targets for therapeutic interventions, especially in patients for whom no antibiotic treatment is possible. Signals that regulate neutrophil recruitment to the lung during mycobacterial infection need to be better understood. We demonstrated here, in the mouse model, that neutrophils were recruited to the lung in two waves after intranasal infection with virulent Mtb or the live attenuated vaccine strain Bacillus Calmette Guérin (BCG). A first wave of neutrophils was swiftly recruited, followed by a subsequent adaptive wave that reached the lung together with IFN-γ- and IL-17A-producing T cells. Interestingly, the second neutrophil wave did not participate to mycobacteria control in the lung and established contacts with T cells. The adaptive wave was critically dependent on the expression of IL-17RA, the receptor for IL-17A, expressed in non-hematopoietic cells. In absence of this receptor, curtailed CXCL-1 and 5 production in the lung restrained neutrophil recruitment. CXCL-1 and 5 instillation reconstituted lung neutrophil recruitment in BCG-infected IL17RA-/- mice.

Vaccination with an Attenuated Mutant of Ehrlichia chaffeensis Induces Pathogen-Specific CD4+ T Cell Immunity and Protection from Tick-Transmitted Wild-Type Challenge in the Canine Host

Ehrlichia chaffeensis is a tick-borne rickettsial pathogen and the causative agent of human monocytic ehrlichiosis. Transmitted by the Amblyomma americanum tick, E. chaffeensis also causes disease in several other vertebrate species including white-tailed deer and dogs. We have recently described the generation of an attenuated mutant strain of E. chaffeensis, with a mutation in the Ech_0660 gene, which is able to confer protection from secondary, intravenous-administered, wild-type E. chaffeensis infection in dogs. Here, we extend our previous results, demonstrating that vaccination with the Ech_0660 mutant protects dogs from physiologic, tick-transmitted, secondary challenge with wild-type E. chaffeensis; and describing, for the first time, the cellular and humoral immune responses induced by Ech_0660 mutant vaccination and wild-type E. chaffeensis infection in the canine host. Both vaccination and infection induced a rise in E. chaffeensis-specific antibody titers and a significant Th1 response in peripheral blood as measured by E. chaffeensis antigen-dependent CD4⁺ T cell proliferation and IFNγ production. Further, we describe for the first time significant IL-17 production by peripheral blood leukocytes from both Ech_0660 mutant vaccinated animals and control animals infected with wild-type E. chaffeensis, suggesting a previously unrecognized role for IL-17 and Th17 cells in the immune response to rickettsial pathogens. Our results are a critical first step towards defining the role of the immune system in vaccine-induced protection from E. chaffeensis infection in an incidental host; and confirm the potential of the attenuated mutant clone, Ech_0660, to be used as a vaccine candidate for protection against tick-transmitted E. chaffeensis infection.

Interleukin-17A as a Biomarker for Bovine Tuberculosis

T helper 17 (Th17)-associated cytokines are integral to the immune responses to tuberculosis, initiating both protective and harmful inflammatory responses. The aim of the present study was to evaluate applied aspects of interleukin-17 (IL-17) biology in the context of Mycobacterium bovis infection of cattle. Using transcriptome sequencing (RNA-Seq), numerous Th17-associated cytokine genes (including IL-17A, IL-17F, IL-22, IL-19, and IL-27) were upregulated >9-fold in response to purified protein derivative stimulation of peripheral blood mononuclear cells from experimentally M. bovis-infected cattle. Protective vaccines elicited IL-17A, IL-17F, IL-22, and IL-27 responses. Reduced IL-17A responses by vaccine recipients, compared to nonvaccinated animals, at 2.5 weeks after M. bovis challenge correlated with reduced disease burdens. Additionally, IL-17A and interferon gamma (IFN-γ) responses were highly correlated and exhibited similar diagnostic capacities. The present findings support the use of Th17-associated cytokines as biomarkers of infection and protection in the immune responses to bovine tuberculosis.

Overexpression of RORγt Enhances Pulmonary Inflammation after Infection with Mycobacterium Avium

Mycobacterium avium complex (MAC) is the most common cause of nontuberculous mycobacterial disease in humans. The role of Th17 immunity in the pathogenesis of intracellular bacteria, such as MAC, is not currently understood. Transcription factor RAR-related orphan receptor gamma t (RORγt) is known as the master regulator for Th17 cell development. Here, we investigated the role of RORγt in host responses against MAC infection. Wild-type (WT) mice and RORγt-overexpressing mice were infected with MAC via intratracheal inoculation. Systemic MAC growth was not different between WT mice and RORγt-overexpressing mice. However, neutrophilic pulmonary inflammation following MAC infection was enhanced in RORγt-overexpressing mice compared with that in WT mice. The cytokine expression shifted toward a Th17 phenotype in the lungs of RORγt-overexpressing mice following MAC infection; the levels of IL-6 and IL-17 were significantly higher in the lung of these mice than in WT mice. In addition to the increase in IL-17 single-positive T cells, T cells producing both IL-17 and interferon-γ were elevated in the lung of RORγt-overexpressing mice following MAC infection. These findings suggest that RORγt overexpression-mediated Th17 bias contributes to local inflammation rather than systemic responses, by regulating neutrophil recruitment into the sites of infection during MAC infection.

Postprimary Tuberculosis and Macrophage Necrosis: Is There a Big ConNECtion?

Adult or postprimary tuberculosis (TB) accounts for most TB cases. Its hallmark is pulmonary cavitation, which occurs as a result of necrosis in the lung in individuals with tuberculous pneumonia. Postprimary TB has previously been known to be associated with vascular thrombosis and delayed-type hypersensitivity, but their roles in pulmonary cavitation are unclear. A necrosis-associated extracellular cluster (NEC) refers to a cluster of drug-tolerant Mycobacterium tuberculosis attached to lysed host materials and is proposed to contribute to granulomatous TB. Here we suggest that NECs, perhaps due to big size, produce a distinct host response leading to postprimary TB. We propose that vascular thrombosis and pneumonia arise from NEC and that these processes are promoted by inflammatory cytokines produced from cell-mediated delayed-type hypersensitivity, such as interleukin-17 and gamma interferon, eventually triggering necrosis in the lung and causing cavitation. According to this view, targeting NEC represents a necessary strategy to control adult TB.

Acquired immunodeficiencies and tuberculosis: focus on HIV/AIDS and diabetes mellitus

The spread of human immunodeficiency virus (HIV) infection within Africa led to marked increases in numbers of cases of tuberculosis (TB), and although the epidemic peaked in 2006, there were still 1.8 million new cases in 2013, with 29.2 million prevalent cases. Half of all TB cases in Africa are in those with HIV co-infection. A brief review of the well-documented main immunological mechanisms of HIV-associated increased susceptibility to TB is presented. However, a new threat is facing TB control, which presents itself in the form of a rapid increase in the number of people living with type II diabetes mellitus (T2DM), particularly in areas that are already hardest hit by the TB epidemic. T2DM increases susceptibility to TB threefold, and the TB burden attributable to T2DM is 15%. This review addresses the much smaller body of research information available on T2DM-TB, compared to HIV-TB comorbidity. We discuss the altered clinical presentation of TB in the context of T2DM comorbidity, changes in innate and adaptive immune responses, including lymphocyte subsets and T-cell phenotypes, the effect of treatment of the different comorbidities, changes in biomarker expression and genetic predisposition to the respective morbidities, and other factors affecting the comorbidity. Although significant gains have been made in improving our understanding of the underlying mechanisms of T2DM-associated increased susceptibility, knowledge gaps still exist that require urgent attention.

Pulmonary but Not Subcutaneous Delivery of BCG Vaccine Confers Protection to Tuberculosis-Susceptible Mice by an Interleukin 17-Dependent Mechanism

Some of the most promising novel tuberculosis vaccine strategies currently under development are based on respiratory vaccination, mimicking the natural route of infection. In this work, we have compared pulmonary and subcutaneous delivery of BCG vaccine in the tuberculosis-susceptible DBA/2 mouse strain, a model in which parenterally administered BCG vaccine does not protect against tuberculosis. Our data show that intranasally but not subcutaneously administered BCG confers robust protection against pulmonary tuberculosis challenge. In addition, our results indicate that pulmonary vaccination triggers a Mycobacterium tuberculosis-specific mucosal immune response orchestrated by interleukin 17A (IL-17A). Thus, IL-17A neutralization in vivo reduces protection and abrogates M. tuberculosis-specific immunoglobulin A (IgA) secretion to respiratory airways and lung expression of polymeric immunoglobulin receptor induced following intranasal vaccination. Together, our results demonstrate that pulmonary delivery of BCG can overcome the lack of protection observed when BCG is given parenterally, suggesting that respiratory tuberculosis vaccines could have an advantage in tuberculosis-endemic countries, where intradermally administered BCG has inefficient effectiveness against pulmonary tuberculosis.

Complexity and Controversies over the Cytokine Profiles of T Helper Cell Subpopulations in Tuberculosis

Tuberculosis (TB) is a contagious infectious disease caused by the TB-causing bacillus Mycobacterium tuberculosis and is considered a public health problem with enormous social impact. Disease progression is determined mainly by the balance between the microorganism and the host defense systems. Although the immune system controls the infection, this control does not necessarily lead to sterilization. Over recent decades, the patterns of CD4+ T cell responses have been studied with a goal of complete understanding of the immunological mechanisms involved in the maintenance of latent or active tuberculosis infection and of the clinical cure after treatment. Conflicting results have been suggested over the years, particularly in studies comparing experimental models and human disease. In recent years, in addition to Th1, Th2, and Th17 profiles, new standards of cellular immune responses, such as Th9, Th22, and IFN-γ-IL-10 double-producing Th cells, discussed here, have also been described. Additionally, many new roles and cellular sources have been described for IL-10, demonstrating a critical role for this cytokine as regulatory, rather than merely pathogenic cytokine, involved in the establishment of chronic latent infection, in the clinical cure after treatment and in keeping antibacillary effector mechanisms active to prevent immune-mediated damage.

Immune requirements for protective Th17 recall responses to Mycobacterium tuberculosis challenge

Tuberculosis (TB) vaccine development has focused largely on targeting T helper type 1 (Th1) cells. However, despite inducing Th1 cells, the recombinant TB vaccine MVA85A failed to enhance protection against TB disease in humans. In recent years, Th17 cells have emerged as key players in vaccine-induced protection against TB. However, the exact cytokine and immune requirements that enable Th17-induced recall protection remain unclear. In this study, we have investigated the requirements for Th17 cell-induced recall protection against Mycobacterium tuberculosis (Mtb) challenge by utilizing a tractable adoptive transfer model in mice. We demonstrate that adoptive transfer of Mtb-specific Th17 cells into naive hosts, and upon Mtb challenge, results in Th17 recall responses that confer protection at levels similar to vaccination strategies. Importantly, although interleukin (IL)-23 is critical, IL-12 and IL-21 are dispensable for protective Th17 recall responses. Unexpectedly, we demonstrate that interferon-γ (IFN-γ) produced by adoptively transferred Th17 cells impairs long-lasting protective recall immunity against Mtb challenge. In contrast, CXCR5 expression is crucial for localization of Th17 cells near macrophages within well-formed B-cell follicles to mediate Mtb control. Thus, our data identify new immune characteristics that can be harnessed to improve Th17 recall responses for enhancing vaccine design against TB.

Innate and Adaptive Cellular Immune Responses to Mycobacterium tuberculosis Infection

Host resistance to Mycobacterium tuberculosis (Mtb) infection requires the coordinated efforts of innate and adaptive immune cells. Diverse pulmonary myeloid cell populations respond to Mtb with unique contributions to both host-protective and potentially detrimental inflammation. Although multiple cell types of the adaptive immune system respond to Mtb infection, CD4 T cells are the principal antigen-specific cells responsible for containment of Mtb infection, but they can also be major contributors to disease during Mtb infection in several different settings. Here, we will discuss the role of different myeloid populations as well as the dual nature of CD4 T cells in Mtb infection with a primary focus on data generated using in vivo cellular immunological studies in experimental animal models and in humans when available.

Impaired M. tuberculosis Antigen-Specific IFN-γ Response without IL-17 Enhancement in Patients with Severe Cavitary Pulmonary Tuberculosis

Background

Th1 cells play an essential role in immune protection against tuberculosis. Th17 cells might be involved with immune pathology in active human tuberculosis (TB). The balance between Th1 and Th17 cells in patients with cavitary tuberculosis needs to be clarified which might help understanding the immunological basis of pathologic pathogenesis in TB.

Method

Initially treated pulmonary TB (PTB) patients with or without cavities were recruited before chemotherapy. We isolated peripheral blood mononuclear cells, stimulated with phytohemagglutinin (PHA), PPD, or ESAT-6 antigens, and assayed supernatant IFN-γ and IL-17 by ELISA after 24 or 72 hours incubation, respectively. Cells were also stained with antibodies to CD3, CD4, CD8, IFN-γ or IL-17 and the proportion of stained cells was measured by flow cytometry.

Results

We found wide variation of IFN-γ response in active PTB patients, but less subject-to-subject variation of IL-17 was observed as we previously reported. There were no significant differences in IFN-γ and IL-17 between cavitary and non-cavitary PTB; however, we found decreased IFN-γ secretion in severe cavitary PTB compared to mild lesion non-cavitary PTB (p < 0.05). We also found a decrease in the proportion of CD3+CD4+ T cells in the blood of severe cavitary PTB patients (p < 0.05).

Conclusions

IL-17 seemed to have no association with the formation of cavities in active PTB from the study of PBMC. Impaired IFN-γ without IL-17 enhancement occurs in peripheral blood during severe cavitary PTB. Our results demonstrate that M. tuberculosis antigen-specific Th1 response is decreased when PTB lesions develop to severe cavities.

Mycobacterium tuberculosis RpfE promotes simultaneous Th1- and Th17-type T-cell immunity via TLR4-dependent maturation of dendritic cells

Reciprocal induction of the Th1 and Th17 immune responses is essential for optimal protection against Mycobacterium tuberculosis (Mtb); however, only a few Mtb antigens are known to fulfill this task. A functional role for resuscitation-promoting factor (Rpf) E, a latency-associated member of the Rpf family, in promoting naïve CD4(+) T-cell differentiation toward both Th1 and Th17 cell fates through interaction with dendritic cells (DCs) was identified in this study. RpfE induces DC maturation by increasing expression of surface molecules and the production of IL-6, IL-1β, IL-23p19, IL-12p70, and TNF-α but not IL-10. This induction is mediated through TLR4 binding and subsequent activation of ERK, p38 MAPKs, and NF-κB signaling. RpfE-treated DCs effectively caused naïve CD4(+) T cells to secrete IFN-γ, IL-2, and IL-17A, which resulted in reciprocal expansions of the Th1 and Th17 cell response along with activation of T-bet and RORγt but not GATA-3. Furthermore, lung and spleen cells from Mtb-infected WT mice but not from TLR4(-/-) mice exhibited Th1 and Th17 polarization upon RpfE stimulation. Taken together, our data suggest that RpfE has the potential to be an effective Mtb vaccine because of its ability to activate DCs that simultaneously induce both Th1- and Th17-polarized T-cell expansion.

Multiplex Analysis of Pro- or Anti-Inflammatory Serum Cytokines and Chemokines in relation to Gender and Age among Tanzanian Tuberculous Lymphadenitis Patients

Objectives. Tuberculous lymphadenitis is the most common form of extrapulmonary tuberculosis (TB) with a female and paediatric preponderance, postulated to be due to differences in the immune response. The aim of this study was to analyze the differences in the serum cytokine levels of tuberculous lymphadenitis patients with respect to age and gender. Methods. A multiplex bead-based enzyme-linked immunosorbent assay was used to measure IFN-γ, TNF-α, GM-CSF, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12, IL-15, and IL-17 levels in sera of patients (n = 86) and healthy controls (n = 23). Results. Levels of IFN-γ, TNF-α, GM-CSF, IL-1β, IL-2, IL-4, and IL-6 were higher in adult patients than in controls, while those of IL-12 were lower (P < 0.05). Children had lower levels of TNF-α, GM-CSF, and IL-5 and higher levels of IL-2 compared with adult patients (P < 0.05). The male adult patients had higher levels of IL-17 and lower levels of IL-12 compared with female adult patients (P < 0.05).  Conclusion. There were significant differences in the levels of circulating cytokines with respect to gender and age. Children had generally lower levels of cytokines as compared to adults, which could make them more susceptible. Findings do not support that female preponderance is due to differences in immune response.

Expression pattern of transcription factors and intracellular cytokines reveals that clinically cured tuberculosis is accompanied by an increase in Mycobacterium-specific Th1, Th2, and Th17 cells

Tuberculosis (TB) remains a major global health problem and is the second biggest cause of death by infectious disease worldwide. Here, we investigate in vitro the Th1, Th2, Th17, and Treg cytokines and transcriptional factors produced after Mycobacterium-specific antigen stimulation in patients with active pulmonary tuberculosis, clinically cured pulmonary tuberculosis, and healthy donors with a positive tuberculin skin test (TST+). Together, our data indicate that clinical cure after treatment increases the percentages of Mycobacterium-specific Th1, Th2, and Th17 cells compared with those found in active-TB and TST+ healthy donors. These results show that the host-parasite equilibrium in latent TB breaks in favor of the microorganism and that the subsequent clinical recovery posttreatment does not return the percentage levels of such cells to those observed in latent tuberculosis. Additionally, our results indicate that rather than showing an increase in the percentage of Mycobacterium-specific Tregs, active-TB patients display lower Th1 : Treg and Th17 : Treg ratios. These data, together with lower Th1 : Th2 and Th17 : Th2 ratios, may indicate a mechanism by which the breakdown of the host-parasite equilibrium leads to active-TB and changes in the repertoire of Mycobacterium-specific Th cells that are associated with clinical cure after treatment of pulmonary tuberculosis.

Inflammation and tuberculosis: host-directed therapies

Tuberculosis (TB) is an airborne infectious disease that kills almost two million individuals every year. Multidrug-resistant (MDR) TB is caused by strains of Mycobacterium tuberculosis (M. tb) resistant to isoniazid and rifampin, the backbone of first-line antitubercular treatment. MDR TB affects an estimated 500,000 new patients annually. Genetic analysis of drug-resistant MDR-TB showed that airborne transmission of undetected and untreated strains played a major role in disease outbreaks. The need for new TB vaccines and faster diagnostics, as well as the development of new drugs, has recently been highlighted. The major problem in terms of current TB research and clinical demands is the increasing number of cases of extensively drug-resistant and 'treatment-refractory' TB. An emerging scenario of adjunct host-directed therapies is intended to target pulmonary TB where inflammatory processes can be deleterious and lead to immune exhaustion. 'Target-organ-saving' strategies may be warranted to prevent damage to infected tissues and achieve focused, clinically relevant and long-lasting anti-M. tb cellular immune responses. Candidates for such interventions may be biological agents or already approved drugs that can be 're-purposed' to interfere with biologically relevant cellular checkpoints. Here, we review current concepts of inflammation in TB disease and discuss candidate pathways for host-directed therapies to achieve better clinical outcomes.

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

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

Cytokine and lipid mediator networks in tuberculosis

A major approach for immunologic intervention in tuberculosis involves redirecting the outcome of the host immune response from the induction of disease to pathogen control. Cytokines and lipid mediators known as eicosanoids play key roles in regulating this balance and as such represent important targets for immunologic intervention. While the evidence for cytokine/eicosanoid function derives largely from the investigation of murine and zebrafish experimental infection models, clinical studies have confirmed the existence of many of the same pathways in tuberculosis patients. Here, we summarize new data that reveal important intersections between the cytokine and eicosanoid networks in the host response to mycobacteria and discuss how targeting this crosstalk can promote resistance to lethal Mycobacterium tuberculosis infection. This approach could lead to new host-directed therapies to be used either as an adjunct for improving the efficacy of standard antibiotic treatment or for the management of drug-resistant infections.

Biology of IL-27 and its role in the host immunity against Mycobacterium tuberculosis

IL-27, a heterodimeric cytokine of IL-12 family, regulates both innate and adaptive immunity largely via Jak-Stat signaling. IL-27 can induce IFN-γ and inflammatory mediators from T lymphocytes and innate immune cells. IL-27 has unique anti-inflammatory properties via both Tr1 cells dependent and independent mechanisms. Here the role and biology of IL-27 in innate and adaptive immunity are summarized, with special interest with immunity against Mycobacterium tuberculosis.

TH17 cells, interleukin-17 and interferon-γ in patients and households contacts of leprosy with multibacillary and paucibacillary forms before and after the start of chemotherapy treatment

BACKGROUND

Studies on the immunology of leprosy are fundamental to the understanding of the various forms of clinical manifestation of the disease. In some diseases, lymphocytes TH17 and one of its key cytokines, interleukin-17 has been shown to be essential in developing an effective immune response. In leprosy, involvement of lymphocyte TH17 and interleukin-17 remains understudied.

OBJECTIVES

This study is the first investigation to examine the association between TH17 cells, interleukin-17 and interferon- γ in patients and households contacts of leprosy.

METHODS

To document the participation of TH17 cells and interleukin-17 in the immunology of leprosy, to observe the behavior of interferon-γ in relation to interleukin-17 and to verify the differences found between individuals paucibacillary, multibacillary and household contacts, we analyzed samples peripheral blood to identify TH-17 cells, interleukin-17 and IFN-γ; establishing relationships between all the groups.

RESULTS

There was a significant difference in the results found in the comparison between the paucibacillary and multibacillary groups of patients (P < 0.001), as well with the household contacts (P < 0.005). The polychemotherapeutic treatment modified the profile of immune response in multibacillary patients compared to what was observed before the start of treatment.

CONCLUSION

The principal finding was that TH17 lymphocytes and interleukin-17 actively participating in the immune response of Hansen's disease as well these cells can stimulate the cellular immunity.

BCG vaccination-induced long-lasting control of Mycobacterium tuberculosis correlates with the accumulation of a novel population of CD4⁺IL-17⁺TNF⁺IL-2⁺ T cells

Mycobacterium bovis Bacille Calmette-Guerin (BCG) is the only vaccine in use to prevent Mycobacterium tuberculosis (Mtb) infection. Here we analyzed the protective efficacy of BCG against Mtb challenges 21 or 120 days after vaccination. Only after 120 days post-vaccination were mice able to efficiently induce early Mtb growth arrest and maintain long-lasting control of Mtb. This protection correlated with the accumulation of CD4(+) T cells expressing IL-17(+)TNF(+)IL-2(+). In contrast, mice challenged with Mtb 21 days after BCG vaccination exhibited only a mild and transient protection, associated with the accumulation of CD4(+) T cells that were mostly IFN-γ(+)TNF(+) and to a lesser extent IFN-γ(+)TNF(+)IL-2(+). These data suggest that the memory response generated by BCG vaccination is functionally distinct depending upon the temporal proximity to BCG vaccination. Understanding how these responses are generated and maintained is critical for the development of novel vaccination strategies against tuberculosis.

A new recombinant BCG vaccine induces specific Th17 and Th1 effector cells with higher protective efficacy against tuberculosis

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis (Mtb) that is a major public health problem. The vaccine used for TB prevention is Mycobacterium bovis bacillus Calmette-Guérin (BCG), which provides variable efficacy in protecting against pulmonary TB among adults. Consequently, several groups have pursued the development of a new vaccine with a superior protective capacity to that of BCG. Here we constructed a new recombinant BCG (rBCG) vaccine expressing a fusion protein (CMX) composed of immune dominant epitopes from Ag85C, MPT51, and HspX and evaluated its immunogenicity and protection in a murine model of infection. The stability of the vaccine in vivo was maintained for up to 20 days post-vaccination. rBCG-CMX was efficiently phagocytized by peritoneal macrophages and induced nitric oxide (NO) production. Following mouse immunization, this vaccine induced a specific immune response in cells from lungs and spleen to the fusion protein and to each of the component recombinant proteins by themselves. Vaccinated mice presented higher amounts of Th1, Th17, and polyfunctional specific T cells. rBCG-CMX vaccination reduced the extension of lung lesions caused by challenge with Mtb as well as the lung bacterial load. In addition, when this vaccine was used in a prime-boost strategy together with rCMX, the lung bacterial load was lower than the result observed by BCG vaccination. This study describes the creation of a new promising vaccine for TB that we hope will be used in further studies to address its safety before proceeding to clinical trials.

Immunity and Immunopathology in the Tuberculous Granuloma

Granulomas, organized aggregates of immune cells, are a defining feature of tuberculosis (TB). Granuloma formation is implicated in the pathogenesis of a variety of inflammatory disorders. However, the tuberculous granuloma has been assigned the role of a host protective structure which "walls-off" mycobacteria. Work conducted over the past decade has provided a more nuanced view of its role in pathogenesis. On the one hand, pathogenic mycobacteria accelerate and exploit granuloma formation for their expansion and dissemination by manipulating host immune responses to turn leukocyte recruitment and cell death pathways in their favor. On the other hand, granuloma macrophages can preserve granuloma integrity by exerting a microbicidal immune response, thus preventing an even more rampant expansion of infection in the extracellular milieu. Even this host-beneficial immune response required to maintain the bacteria intracellular must be tempered, as an overly vigorous immune response can also cause granuloma breakdown, thereby directly supporting bacterial growth extracellularly. This review will discuss how mycobacteria manipulate inflammatory responses to drive granuloma formation and will consider the roles of the granuloma in pathogenesis and protective immunity, drawing from clinical studies of TB in humans and from animal models--rodents, zebrafish, and nonhuman primates. A deeper understanding of TB pathogenesis and immunity in the granuloma could suggest therapeutic approaches to abrogate the host-detrimental aspects of granuloma formation to convert it into the host-beneficial structure that it has been thought to be for nearly a century.

Orchestration of pulmonary T cell immunity during Mycobacterium tuberculosis infection: immunity interruptus

Despite the introduction almost a century ago of Mycobacterium bovis BCG (BCG), an attenuated form of M. bovis that is used as a vaccine against Mycobacterium tuberculosis, tuberculosis remains a global health threat and kills more than 1.5 million people each year. This is mostly because BCG fails to prevent pulmonary disease--the contagious form of tuberculosis. Although there have been significant advances in understanding how the immune system responds to infection, the qualities that define protective immunity against M. tuberculosis remain poorly characterized. The ability to predict who will maintain control over the infection and who will succumb to clinical disease would revolutionize our approach to surveillance, control, and treatment. Here we review the current understanding of pulmonary T cell responses following M. tuberculosis infection. While infection elicits a strong immune response that contains infection, M. tuberculosis evades eradication. Traditionally, its intracellular lifestyle and alteration of macrophage function are viewed as the dominant mechanisms of evasion. Now we appreciate that chronic inflammation leads to T cell dysfunction. While this may arise as the host balances the goals of bacterial sterilization and avoidance of tissue damage, it is becoming clear that T cell dysfunction impairs host resistance. Defining the mechanisms that lead to T cell dysfunction is crucial as memory T cell responses are likely to be subject to the same subject to the same pressures. Thus, success of T cell based vaccines is predicated on memory T cells avoiding exhaustion while at the same time not promoting overt tissue damage.

Agreement between QuantiFERON®-TB Gold In-Tube and the tuberculin skin test and predictors of positive test results in Warao Amerindian pediatric tuberculosis contacts

Background

Interferon-gamma release assays have emerged as a more specific alternative to the tuberculin skin test (TST) for detection of tuberculosis (TB) infection, especially in Bacille Calmette-Guérin (BCG) vaccinated people. We determined the prevalence of Mycobacterium tuberculosis infection by TST and QuantiFERON^®-TB Gold In-Tube (QFT-GIT) and assessed agreement between the two test methods and factors associated with positivity in either test in Warao Amerindian children in Venezuela. Furthermore, progression to active TB disease was evaluated for up to 12 months.

Methods

163 HIV-negative childhood household contacts under 16 years of age were enrolled for TST, QFT-GIT and chest X-ray (CXR). Follow-up was performed at six and 12 months. Factors associated with TST and QFT-GIT positivity were studied using generalized estimation equations logistic regression models.

Results

At baseline, the proportion of TST positive children was similar to the proportion of children with a positive QFT-GIT (47% vs. 42%, p = 0.12). Overall concordance between QFT-GIT and TST was substantial (kappa 0.76, 95% CI 0.46-1.06). Previous BCG vaccination was not associated with significantly increased positivity in either test (OR 0.68, 95% CI 0.32-1.5 for TST and OR 0.51, 95% CI 0.14-1.9 for QFT-GIT). Eleven children were diagnosed with active TB at baseline. QFT-GIT had a higher sensitivity for active TB (88%, 95% CI 47-98%) than TST (55%, 95% CI 24-83%) while specificities were similar (respectively 58% and 55%). Five initially asymptomatic childhood contacts progressed to active TB disease during follow-up.

Conclusion

Replacement of TST by the QFT-GIT for detection of M. tuberculosis infection is not recommended in this resource-constrained setting as test results showed substantial concordance and TST positivity was not affected by previous BCG vaccination. The QFT-GIT had a higher sensitivity than the TST for the detection of TB disease. However, the value of the QFT-GIT as an adjunct in diagnosing TB disease is limited by a high variability in QFT-GIT results over time.

The frequencies of IFNγ+IL2+TNFα+ PPD-specific CD4+CD45RO+ T-cells correlate with the magnitude of the QuantiFERON® gold in-tube response in a prospective study of healthy indian adolescents

BACKGROUND

QuantiFERON-TB Gold In-Tube (QFT) is an IFNγ-release assay used in the diagnosis of Mycobacterium tuberculosis (MTB) infection. The risk of TB progression increases with the magnitude of the MTB-specific IFNγ-response. QFT reversion, also associated with low Tuberculin Skin Test responses, may therefore represent a transient immune response with control of M. tuberculosis infection. However, studies at the single cell level have suggested that the quality (polyfunctionality) of the T-cell response is more important than the quantity of cytokines produced.

OBJECTIVE

To explore the quality and/or magnitude of mycobacteria-specific T-cell responses associated with QFT reversion and persistent QFT-positivity.

METHODS

Multi-color flowcytometry on prospectively collected peripheral blood mononuclear cells was applied to assess mycobacteria-specific T-cell responses in 42 QFT positive Indian adolescents of whom 21 became QFT negative (reverters) within one year. Ten QFT consistent negatives were also included as controls.

RESULTS

There was no difference in the qualitative PPD-specific CD4+ T-cell response between QFT consistent positives and reverters. However, compared with QFT consistent positives, reverters displayed lower absolute frequencies of polyfunctional (IFNγ+IL2+TNFα+) CD4+ T-cells at baseline, which were further reduced to the point where they were not different to QFT negative controls one year later. Moreover, absolute frequencies of these cells correlated well with the magnitude of the QFT-response.

CONCLUSION

Whereas specific polyfunctional CD4+ T-cells have been suggested to protect against TB progression, our data do not support that higher relative or absolute frequencies of PPD-specific polyfunctional CD4+ T-cells in peripheral blood can explain the reduced risk of TB progression observed in QFT reverters. On the contrary, absolute frequencies of these cells correlated with the QFT-response, suggesting that this readout reflects antigenic load.

Directing traffic: IL-17 and IL-22 coordinate pulmonary immune defense

Respiratory infections and diseases are among the leading causes of death worldwide, and effective treatments probably require manipulating the inflammatory response to pathogenic microbes or allergens. Here, we review mechanisms controlling the production and functions of interleukin-17 (IL-17) and IL-22, cytokines that direct several aspects of lung immunity. Innate lymphocytes (γδ T cells, natural killer cells, innate lymphoid cells) are the major source of IL-17 and IL-22 during acute infections, while CD4(+) T-helper 17 (Th17) cells contribute to vaccine-induced immunity. The characterization of dendritic cell (DC) subsets has revealed their central roles in T-cell activation. CD11b(+) DCs stimulated with bacteria or fungi secrete IL-1β and IL-23, potent inducers of IL-17 and IL-22. On the other hand, recognition of viruses by plasmacytoid DCs inhibits IL-1β and IL-23 release, increasing susceptibility to bacterial superinfections. IL-17 and IL-22 primarily act on the lung epithelium, inducing antimicrobial proteins and neutrophil chemoattractants. Recent studies found that stimulation of macrophages and DCs with IL-17 also contributes to antibacterial immunity, while IL-22 promotes epithelial proliferation and repair following injury. Chronic diseases such as asthma and chronic obstructive pulmonary disease have been associated with IL-17 and IL-22 responses directed against innocuous antigens. Future studies will evaluate the therapeutic efficacy of targeting the IL-17/IL-22 pathway in pulmonary inflammation.

Novel vaccination strategies against tuberculosis

The tuberculosis (TB) pandemic continues to rampage despite widespread use of the BCG (Bacillus Calmette-Guérin) vaccine. Novel vaccination strategies are urgently needed to arrest global transmission and prevent the uncontrolled development of multidrug-resistant forms of Mycobacterium tuberculosis. Over the last two decades, considerable progress has been made in the field of vaccine development with numerous innovative preclinical candidates and more than a dozen vaccines in clinical trials. These vaccines are developed either as boosters of the current BCG vaccine or as novel prime vaccines to replace BCG. Given the enormous prevalence of latent TB infection, vaccines that are protective on top of an already established infection remain a high priority and a significant scientific challenge. Here we discuss the current state of TB vaccine research and development, our understanding of the underlying immunology, and the requirements for an efficient TB vaccine.

Recent advances towards tuberculosis control: vaccines and biomarkers

Of all infectious diseases, tuberculosis (TB) remains one of the most important causes of morbidity and mortality. Recent advances in understanding the biology of Mycobacterium tuberculosis (Mtb) infection and the immune response of the infected host have led to the development of several new vaccines, a number of which are already undergoing clinical trials. These include pre-exposure prime vaccines, which could replace bacille Calmette-Guérin (BCG), and pre-exposure booster vaccines given in addition to BCG. Infants are the target population of these two types of vaccines. In addition, several postexposure vaccines given during adolescence or adult life, in addition to BCG as a priming vaccine during infancy, are undergoing clinical testing. Therapeutic vaccines are currently being assessed for their potential to cure active TB as an adjunct to chemotherapy. BCG replacement vaccines are viable recombinant BCG or double-deletion mutants of Mtb. All booster vaccines are composed of one or several antigens, either expressed by viral vectors or formulated with adjuvants. Therapeutic vaccines are killed mycobacterial preparations. Finally, multivariate biomarkers and biosignatures are being generated from high-throughput data with the aim of providing better diagnostic tools to specifically determine TB progression. Here, we provide a technical overview of these recent developments as well of the relevant computational approaches and highlight the obstacles that still need to be overcome.

Progress in tuberculosis vaccine development and host-directed therapies--a state of the art review

Tuberculosis continues to kill 1·4 million people annually. During the past 5 years, an alarming increase in the number of patients with multidrug-resistant tuberculosis and extensively drug-resistant tuberculosis has been noted, particularly in eastern Europe, Asia, and southern Africa. Treatment outcomes with available treatment regimens for drug-resistant tuberculosis are poor. Although substantial progress in drug development for tuberculosis has been made, scientific progress towards development of interventions for prevention and improvement of drug treatment outcomes have lagged behind. Innovative interventions are therefore needed to combat the growing pandemic of multidrug-resistant and extensively drug-resistant tuberculosis. Novel adjunct treatments are needed to accomplish improved cure rates for multidrug-resistant and extensively drug-resistant tuberculosis. A novel, safe, widely applicable, and more effective vaccine against tuberculosis is also desperately sought to achieve disease control. The quest to develop a universally protective vaccine for tuberculosis continues. So far, research and development of tuberculosis vaccines has resulted in almost 20 candidates at different stages of the clinical trial pipeline. Host-directed therapies are now being developed to refocus the anti-Mycobacterium tuberculosis-directed immune responses towards the host; a strategy that could be especially beneficial for patients with multidrug-resistant tuberculosis or extensively drug-resistant tuberculosis. As we are running short of canonical tuberculosis drugs, more attention should be given to host-directed preventive and therapeutic intervention measures.

Mycobacterium tuberculosis impairs dendritic cell functions through the serine hydrolase Hip1

Mycobacterium tuberculosis is a highly successful human pathogen that primarily resides in host phagocytes, such as macrophages and dendritic cells (DCs), and interferes with their functions. Although multiple strategies used by M. tuberculosis to modulate macrophage responses have been discovered, interactions between M. tuberculosis and DCs are less well understood. DCs are the primary APCs of the immune system and play a central role in linking innate and adaptive immune responses to microbial pathogens. In this study, we show that M. tuberculosis impairs DC cytokine secretion, maturation, and Ag presentation through the cell envelope-associated serine hydrolase, Hip1. Compared to wild-type, a hip1 mutant strain of M. tuberculosis induced enhanced levels of the key Th1-inducing cytokine IL-12, as well as other proinflammatory cytokines (IL-23, IL-6, TNF-α, IL-1β, and IL-18) in DCs via MyD88- and TLR2/9-dependent pathways, indicating that Hip1 restricts optimal DC inflammatory responses. Infection with the hip1 mutant also induced higher levels of MHC class II and costimulatory molecules CD40 and CD86, indicating that M. tuberculosis impairs DC maturation through Hip1. Further, we show that M. tuberculosis promotes suboptimal Ag presentation, as DCs infected with the hip1 mutant showed increased capacity to present Ag to OT-II- and early secreted antigenic target 6-specific transgenic CD4 T cells and enhanced Th1 and Th17 polarization. Overall, these data show that M. tuberculosis impairs DC functions and modulates the nature of Ag-specific T cell responses, with important implications for vaccination strategies.

Novel vaccine approaches for protection against intracellular pathogens

Vaccination against intracellular pathogens requires generation of a pool of memory T cells able to respond upon infection and mediate either killing of the infected cell or induce killing mechanisms in the infected cell. T cell-inducing vaccines must aim to target the antigen to antigen-presenting cells (APCs) so that it can be presented on MHC molecules on the cell surface. Methods to do this include making use of vectors such as plasmid DNA or viruses, live attenuated pathogens or subunit vaccines targeted and enhanced using adjuvants. The choice of approach should be guided by the phenotype and localization of the desired T cell response. This review will discuss current approaches in the pipeline for the development of T cell-inducing vaccines, including vectored, live attenuated, and subunit vaccines.

In search of a new paradigm for protective immunity to TB

Clinical trials of vaccines against Mycobacterium tuberculosis are well under way and results are starting to come in. Some of these results are not so encouraging, as exemplified by the latest Aeras-422 and MVA85A trials. Other than empirically determining whether a vaccine reduces the number of cases of active tuberculosis, which is a daunting prospect given the chronic nature of the disease, we have no way of assessing vaccine efficacy. Therefore, investigators seek to identify biomarkers that predict vaccine efficacy. Historically, focus has been on the production of interferon-γ by CD4(+) T cells, but this has not been a useful correlate of vaccine-induced protection. In this Opinion article, we discuss recent advances in our understanding of the immune control of M. tuberculosis and how this knowledge could be used for vaccine design and evaluation.

CD4+ T cells contain early extrapulmonary tuberculosis (TB) dissemination and rapid TB progression and sustain multieffector functions of CD8+ T and CD3- lymphocytes: mechanisms of CD4+ T cell immunity

The possibility that CD4(+) T cells can act as "innate-like" cells to contain very early Mycobacterium tuberculosis dissemination and function as master helpers to sustain multiple effector functions of CD8(+) T cells and CD3(-) lymphocytes during development of adaptive immunity against primary tuberculosis (TB) has not been demonstrated. We showed that pulmonary M. tuberculosis infection of CD4-depleted macaques surprisingly led to very early extrapulmonary M. tuberculosis dissemination, whereas CD4 deficiency clearly resulted in rapid TB progression. CD4 depletion during M. tuberculosis infection revealed the ability of CD8(+) T cells to compensate and rapidly differentiate to Th17-like/Th1-like and cytotoxic-like effectors, but these effector functions were subsequently unsustainable due to CD4 deficiency. Whereas CD3(-) non-T lymphocytes in the presence of CD4(+) T cells developed predominant Th22-like and NK-like (perforin production) responses to M. tuberculosis infection, CD4 depletion abrogated these Th22-/NK-like effector functions and favored IL-17 production by CD3(-) lymphocytes. CD4-depleted macaques exhibited no or few pulmonary T effector cells constitutively producing IFN-γ, TNF-α, IL-17, IL-22, and perforin at the endpoint of more severe TB, but they presented pulmonary IL-4(+) T effectors. TB granulomas in CD4-depleted macaques contained fewer IL-22(+) and perforin(+) cells despite the presence of IL-17(+) and IL-4(+) cells. These results implicate a previously unknown innate-like ability of CD4(+) T cells to contain extrapulmonary M. tuberculosis dissemination at very early stage. Data also suggest that CD4(+) T cells are required to sustain multiple effector functions of CD8(+) T cells and CD3(-) lymphocytes and to prevent rapid TB progression during M. tuberculosis infection of nonhuman primates.

Protective CD4 T cells targeting cryptic epitopes of Mycobacterium tuberculosis resist infection-driven terminal differentiation

CD4 T cells are crucial to the control of Mycobacterium tuberculosis infection and are a key component of current vaccine strategies. Conversely, immune-mediated pathology drives disease, and recent evidence suggests that adaptive and innate responses are evolutionarily beneficial to M. tuberculosis. We compare the functionality of CD4 T cell responses mounted against dominant and cryptic epitopes of the M. tuberculosis 6-kDa early secreted Ag (ESAT-6) before and postinfection. Protective T cells against cryptic epitopes not targeted during natural infection were induced by vaccinating mice with a truncated ESAT-6 protein, lacking the dominant epitope. The ability to generate T cells that recognize multiple cryptic epitopes was MHC-haplotype dependent, including increased potential via heterologous MHC class II dimers. Before infection, cryptic epitope-specific T cells displayed enhanced proliferative capacity and delayed cytokine kinetics. After aerosol M. tuberculosis challenge, vaccine-elicited CD4 T cells expanded and recruited to the lung. In chronic infection, dominant epitope-specific T cells developed a terminal differentiated KLRG1(+)/PD-1(lo) surface phenotype that was significantly reduced in the cryptic epitope-specific T cell populations. Dominant epitope-specific T cells in vaccinated animals developed into IFN-γ- and IFN-γ,TNF-α-coproducing effector cells, characteristic of the endogenous response. In contrast, cryptic epitope-specific CD4 T cells maintained significantly greater IFN-γ(+)TNF-α(+)IL-2(+) and TNF-α(+)IL-2(+) memory-associated polyfunctionality and enhanced proliferative capacity. Vaccine-associated IL-17A production by cryptic CD4 T cells was also enhanced, but without increased neutrophilia/pathology. Direct comparison of dominant/cryptic epitope-specific CD4 T cells within covaccinated mice confirmed the superior ability of protective cryptic epitope-specific T cells to resist M. tuberculosis infection-driven T cell differentiation.

Relevance of bovine tuberculosis research to the understanding of human disease: historical perspectives, approaches, and immunologic mechanisms

Pioneer studies on infectious disease and immunology by Jenner, Pasteur, Koch, Von Behring, Nocard, Roux, and Ehrlich forged a path for the dual-purpose with dual benefit approach, demonstrating a profound relevance of veterinary studies for biomedical applications. Tuberculosis (TB), primarily due to Mycobacterium tuberculosis in humans and Mycobacterium bovis in cattle, is an exemplary model for the demonstration of this concept. Early studies with cattle were instrumental in the development of the use of Koch's tuberculin as an in vivo measure of cell-mediated immunity for diagnostic purposes. Calmette and Guerin demonstrated the efficacy of an attenuated M. bovis strain (BCG) in cattle prior to use of this vaccine in humans. The interferon-γ release assay, now widely used for TB diagnosis in humans, was developed circa 1990 for use in the Australian bovine TB eradication program. More recently, M. bovis infection and vaccine efficacy studies with cattle have demonstrated a correlation of vaccine-elicited T cell central memory (TCM) responses to vaccine efficacy, correlation of specific antibody to mycobacterial burden and lesion severity, and detection of antigen-specific IL-17 responses to vaccination and infection. Additionally, positive prognostic indicators of bovine TB vaccine efficacy (i.e., responses measured after infection) include: reduced antigen-specific IFN-γ, iNOS, IL-4, and MIP1-α responses; reduced antigen-specific expansion of CD4(+) T cells; and a diminished activation profile on T cells within antigen stimulated cultures. Delayed type hypersensitivity and IFN-γ responses correlate with infection but do not necessarily correlate with lesion severity whereas antibody responses generally correlate with lesion severity. Recently, serologic tests have emerged for the detection of tuberculous animals, particularly elephants, captive cervids, and camelids. B cell aggregates are consistently detected within tuberculous lesions of humans, cattle, mice and various other species, suggesting a role for B cells in the immunopathogenesis of TB. Comparative immunology studies including partnerships of researchers with veterinary and medical perspectives will continue to provide mutual benefit to TB research in both man and animals.

S100A8/A9 proteins mediate neutrophilic inflammation and lung pathology during tuberculosis

RATIONALE

A hallmark of pulmonary tuberculosis (TB) is the formation of granulomas. However, the immune factors that drive the formation of a protective granuloma during latent TB, and the factors that drive the formation of inflammatory granulomas during active TB, are not well defined.

OBJECTIVES

The objective of this study was to identify the underlying immune mechanisms involved in formation of inflammatory granulomas seen during active TB.

METHODS

The immune mediators involved in inflammatory granuloma formation during TB were assessed using human samples and experimental models of Mycobacterium tuberculosis infection, using molecular and immunologic techniques.

MEASUREMENTS AND MAIN RESULTS

We demonstrate that in human patients with active TB and in nonhuman primate models of M. tuberculosis infection, neutrophils producing S100 proteins are dominant within the inflammatory lung granulomas seen during active TB. Using the mouse model of TB, we demonstrate that the exacerbated lung inflammation seen as a result of neutrophilic accumulation is dependent on S100A8/A9 proteins. S100A8/A9 proteins promote neutrophil accumulation by inducing production of proinflammatory chemokines and cytokines, and influencing leukocyte trafficking. Importantly, serum levels of S100A8/A9 proteins along with neutrophil-associated chemokines, such as keratinocyte chemoattractant, can be used as potential surrogate biomarkers to assess lung inflammation and disease severity in human TB.

CONCLUSIONS

Our results thus show a major pathologic role for S100A8/A9 proteins in mediating neutrophil accumulation and inflammation associated with TB. Thus, targeting specific molecules, such as S100A8/A9 proteins, has the potential to decrease lung tissue damage without impacting protective immunity against TB.

Effects of Bacille Calmette-Guerin after the first demyelinating event in the CNS

OBJECTIVE

To evaluate Bacille Calmette-Guérin (BCG) effects after clinically isolated syndromes (CIS).

METHODS

In a double-blind, placebo-controlled trial, participants were randomly assigned to receive BCG or placebo and monitored monthly with brain MRI (6 scans). Both groups then entered a preplanned phase with IM interferon-β-1a for 12 months. From month 18 onward, the patients took the disease-modifying therapies (DMTs) that their neurologist considered indicated in an open-label extension phase lasting up to 60 months.

RESULTS

Of 82 randomized subjects, 73 completed the study (33 vaccinated and 40 placebo). During the initial 6 months, the number of cumulative lesions was significantly lower in vaccinated people. The relative risks were 0.541 (95% confidence interval [CI] 0.308-0.956; p = 0.03) for gadolinium-enhancing lesions (the primary endpoint), 0.364 (95% CI 0.207-0.639; p = 0.001) for new and enlarging T2-hyperintense lesions, and 0.149 (95% CI 0.046-0.416; p = 0.001) for new T1-hypointense lesions. The number of total T1-hypointense lesions was lower in the BCG group at months 6, 12, and 18: mean changes from baseline were -0.09 ± 0.72 vs 0.75 ± 1.81 (p = 0.01), 0.0 ± 0.83 vs 0.88 ± 2.21 (p = 0.08), and -0.21 ± 1.03 vs 1.00 ± 2.49 (p = 0.02). After 60 months, the cumulative probability of clinically definite multiple sclerosis was lower in the BCG + DMT arm (hazard ratio = 0.52, 95% CI 0.27-0.99; p < 0.05), and more vaccinated people remained DMT-free (odds ratio = 0.20, 95% CI 0.04-0.93; p = 0.04).

CONCLUSIONS

Early BCG may benefit CIS and affect its long-term course.

CLASSIFICATION OF EVIDENCE

BCG, as compared to placebo, was associated with significantly reduced development of gadolinium-enhancing lesions in people with CIS for a 6-month period before starting immunomodulating therapy (Class I evidence).

A role for interleukin-17A in modulating intracellular survival of Mycobacterium bovis bacillus Calmette-Guérin in murine macrophages

Interleukin 17A IL-17A is a crucial immunomodulator in various chronic immunological diseases including rheumatoid arthritis and inflammatory bowel disease. The cytokine has also been demonstrated to control the pathogenesis of the Mycobacterium tuberculosis by dysregulating production of cytokines and chemokines and promoting granuloma formation. Whether IL-17A regulates innate defence mechanisms of macrophages in response to mycobacterial infection remains to be elucidated. In the current report, we investigated the effects of IL-17A on modulating the intracellular survival of Mycobacterium bovis bacillus Calmette-Guérin (BCG) in RAW264.7 murine macrophages. We observed that IL-17A pre-treatment for 24 hr was able to synergistically enhance BCG-induced nitric oxide (NO) production and inducible nitric oxide synthase expression in dose- and time-dependent manners. We further delineated the mechanisms involved in this synergistic reaction. IL-17A was found to specifically enhanced BCG-induced phosphorylation of Jun N-terminal kinase (JNK), but not of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase. By using a specific JNK inhibitor (SP600125), we found that the production of NO in BCG-infected macrophages was significantly suppressed. Taken together, we confirmed the involvement of the JNK pathway in IL-17A-enhanced NO production in BCG-infected macrophages. We further demonstrated that IL-17A significantly enhanced the clearance of intracellular BCG by macrophages through an NO-dependent killing mechanism. In conclusion, our study revealed an anti-mycobacterial role of IL-17A through priming the macrophages to produce NO in response to mycobacterial infection.

Mice genetically inactivated in interleukin-17A receptor are defective in long-term control of Mycobacterium tuberculosis infection

Interleukin-17A (IL-17A), a pro-inflammatory cytokine acting on neutrophil recruitment, is known to play an important role during Mycobacterium tuberculosis infection, but the role of IL-17A receptor signalling in immune defence against this intracellular pathogen remains poorly documented. Here we have analysed this signalling using C57BL/6 mice genetically inactivated in the IL-17 receptor A subunit (IL-17RA(-/-) ). Although early after infection bacterial growth was controlled to the same extent as in wild-type mice, IL-17RA(-/-) mice were defective in exerting long-term control of M. tuberculosis infection, as demonstrated by a progressively increasing pulmonary bacterial burden and shortened survival time. Compared with infected wild-type mice, IL-17RA(-/-) mice showed impaired recruitment of neutrophils to the lungs at the early but not the late stage of infection. Pulmonary tumour necrosis factor-α, IL-6 and particularly IL-10 levels were decreased in the absence of IL-17RA signalling, whereas IL-1β was increased. CD4(+) -mediated and γδ-mediated IL-17A production was dramatically increased in IL-17RA(-/-) mice (confirming part of their phenotype), whereas production of interferon-γ and expression of the bactericidal enzyme inducible nitric oxide synthase were not affected. Collectively, our data suggest that early but not late neutrophil recruitment is essential for IL-17A-mediated long-term control of M. tuberculosis infection and that a functional interferon-γ response is not sufficient to control M. tuberculosis growth when the IL-17RA pathway is deficient. As treatment of auto-immune diseases with anti-IL-17A antibodies is actually being tested in clinical studies, our data suggest that caution should be taken with respect to possible reactivation of tuberculosis.

Dynamics of immune effector mechanisms during infection with Mycobacterium avium in C57BL/6 mice

Opportunistic infections with non-tuberculous mycobacteria such as Mycobacterium avium are receiving renewed attention because of increased incidence and difficulties in treatment. As for other mycobacterial infections, a still poorly understood collaboration of different immune effector mechanisms is required to confer protective immunity. Here we have characterized the interplay of innate and adaptive immune effector mechanisms contributing to containment in a mouse infection model using virulent M. avium strain 104 in C57BL/6 mice. M. avium caused chronic infection in mice, as shown by sustained organ bacterial load. In the liver, bacteria were contained in granuloma-like structures that could be defined morphologically by expression of the antibacterial innate effector protein Lipocalin 2 in the adjoining hepatocytes and infiltrating neutrophils, possibly contributing to containment. Circulatory anti-mycobacterial antibodies steadily increased throughout infection and were primarily of the IgM isotype. Highest levels of interferon-γ were found in infected liver, spleen and serum of mice approximately 2 weeks post infection and coincided with a halt in organ bacterial growth. In contrast, expression of tumour necrosis factor was surprisingly low in spleen compared with liver. We did not detect interleukin-17 in infected organs or M. avium-specific T helper 17 cells, suggesting a minor role for T helper 17 cells in this model. A transient and relative decrease in regulatory T cell numbers was seen in spleens. This detailed characterization of M. avium infection in C57BL/6 mice may provide a basis for future studies aimed at gaining better insight into mechanisms leading to containment of infections with non-tuberculous mycobacteria.

Systems approach to tuberculosis vaccine development

Tuberculosis is both highly prevalent across the world and eludes our attempts to control it. The current bacillus Calmette-Guérin vaccine has unreliable protection against adult pulmonary tuberculosis. As a result, tuberculosis vaccine development has been an ongoing area of research for several decades. Only recently have research efforts resulted in the development of several vaccine candidates that are further along in clinical trials. The majority of the barriers surrounding tuberculosis vaccine development are related to the lack of defined biomarkers for tuberculosis protective immunity and the lack of understanding of the complex interactions between the host and pathogen in the human immune system. As a result, testing various antigens discovered through molecular biology techniques have been only with surrogates of protection and do not accurately predict protective immunity. This review will address new discoveries in latency antigens and new next-generation candidate vaccines that promise the possibility of sterile eradication. Also discussed are the potentially important roles of systems biology and vaccinomics in shortening development of an efficacious tuberculosis vaccine through utilization of high-throughput technology, computer modelling and integrative approaches.

Mycobacterium tuberculosis PstS1 amplifies IFN-γ and induces IL-17/IL-22 responses by unrelated memory CD4+ T cells via dendritic cell activation

The immunological mechanisms that modulate protection during Mycobacterium tuberculosis (Mtb) infection or vaccination are not fully understood. Secretion of IFN-γ and, to a lesser extent, of IL-17 by CD4(+) T cells plays a major role both in protection and immunopathology. Few Mtb Ags interacting with DCs affect priming, activation, and regulation of Ag-unrelated CD4(+) T-cell responses. Here we demonstrate that PstS1, a 38 kDa-lipoprotein of Mtb, promotes Ag-independent activation of memory T lymphocytes specific for Ag85B or Ag85A, two immunodominant protective Ags of Mtb. PstS1 expands CD4(+) and CD8(+) memory T cells, amplifies secretion of IFN-γ and IL-22 and induces IL-17 production by effector memory cells in an Ag-unrelated manner in vitro and in vivo. These effects were mediated through the stimulation of DCs, particularly of the CD8α(-) subtype, which respond to PstS1 by undergoing phenotypic maturation and by secreting IL-6, IL-1β and, to a lower extent, IL-23. IL-6 secretion by PstS1-stimulated DCs was required for IFN-γ, and to a lesser extent for IL-22 responses by Ag85B-specific memory T cells. These results may open new perspectives for immunotherapeutic strategies to control Th1/Th17 immune responses in Mtb infections and in vaccinations against tuberculosis.

Interleukin-17-dependent CXCL13 mediates mucosal vaccine-induced immunity against tuberculosis

The variable efficacy of tuberculosis (TB) vaccines and the emergence of drug-resistant strains of Mycobacterium tuberculosis (Mtb) emphasize the urgency for not only generating new and more effective vaccines against TB but also understanding the underlying mechanisms that mediate vaccine-induced protection. We demonstrate that mucosal adjuvants, such as type II heat labile enterotoxin (LT-IIb), delivered through the mucosal route induce pulmonary Mtb-specific T helper type 17 (Th17) responses and provide vaccine-induced protection against Mtb infection. Importantly, protection is interferon-γ (IFNγ)-independent but interleukin-17 (IL-17)-dependent. Our data show that IL-17 mediates C-X-C motif chemokine ligand 13 (CXCL13) induction in the lung for strategic localization of proinflammatory cytokine-producing CXCR5+ (C-X-C motif chemokine receptor 5-positive) T cells within lymphoid structures, thereby promoting early and efficient macrophage activation and the control of Mtb. Our studies highlight the potential value of targeting the IL-17-CXCL13 pathway rather than the IFNγ pathway as a new strategy to improve mucosal vaccines against TB.

TLR9 activation dampens the early inflammatory response to Paracoccidioides brasiliensis, impacting host survival

BACKGROUND

Paracoccidioides brasiliensis causes paracoccidioidomycosis, one of the most prevalent systemic mycosis in Latin America. Thus, understanding the characteristics of the protective immune response to P. brasiliensis is of interest, as it may reveal targets for disease control. The initiation of the immune response relies on the activation of pattern recognition receptors, among which are TLRs. Both TLR2 and TLR4 have been implicated in the recognition of P. brasiliensis and regulation of the immune response. However, the role of TLR9 during the infection by this fungus remains unclear.

METHODOLOGY/PRINCIPAL FINDINGS

We used in vitro and in vivo models of infection by P. brasiliensis, comparing wild type and TLR9 deficient ((-/-)) mice, to assess the contribution of TLR9 on cytokine induction, phagocytosis and outcome of infection. We show that TLR9 recognizes either the yeast form or DNA from P. brasiliensis by stimulating the expression/production of pro-inflammatory cytokines by bone marrow derived macrophages, also increasing their phagocytic ability. We further show that TLR9 plays a protective role early after intravenous infection with P. brasiliensis, as infected TLR9(-/-) mice died at higher rate during the first 48 hours post infection than wild type mice. Moreover, TLR9(-/-) mice presented tissue damage and increased expression of several cytokines, such as TNF-α and IL-6. The increased pattern of cytokine expression was also observed during intraperitoneal infection of TLR9(-/-) mice, with enhanced recruitment of neutrophils. The phenotype of TLR9(-/-) hosts observed during the early stages of P. brasiliensis infection was reverted upon a transient, 48 hours post-infection, neutrophil depletion.

CONCLUSIONS/SIGNIFICANCE

Our results suggest that TLR9 activation plays an early protective role against P. brasiliensis, by avoiding a deregulated type of inflammatory response associated to neutrophils that may lead to tissue damage. Thus modulation of TLR9 may be of interest to potentiate the host response against this pathogen.

B cells regulate neutrophilia during Mycobacterium tuberculosis infection and BCG vaccination by modulating the interleukin-17 response

We have previously demonstrated that B cells can shape the immune response to Mycobacterium tuberculosis, including the level of neutrophil infiltration and granulomatous inflammation at the site of infection. The present study examined the mechanisms by which B cells regulate the host neutrophilic response upon exposure to mycobacteria and how neutrophilia may influence vaccine efficacy. To address these questions, a murine aerosol infection tuberculosis (TB) model and an intradermal (ID) ear BCG immunization mouse model, involving both the μMT strain and B cell-depleted C57BL/6 mice, were used. IL (interleukin)-17 neutralization and neutrophil depletion experiments using these systems provide evidence that B cells can regulate neutrophilia by modulating the IL-17 response during M. tuberculosis infection and BCG immunization. Exuberant neutrophilia at the site of immunization in B cell-deficient mice adversely affects dendritic cell (DC) migration to the draining lymph nodes and attenuates the development of the vaccine-induced Th1 response. The results suggest that B cells are required for the development of optimal protective anti-TB immunity upon BCG vaccination by regulating the IL-17/neutrophilic response. Administration of sera derived from M. tuberculosis-infected C57BL/6 wild-type mice reverses the lung neutrophilia phenotype in tuberculous μMT mice. Together, these observations provide insight into the mechanisms by which B cells and humoral immunity modulate vaccine-induced Th1 response and regulate neutrophila during M. tuberculosis infection and BCG immunization.

Mycobacterium tuberculosis poses a serious threat to public health globally. It has been well established that T cells are critical in protection against M. tuberculosis. The role of B cells and humoral immunity in the process is less well understood. We previously showed that B cells and humoral immunity regulate the immune response against M. tuberculosis. The present study examined the mechanisms by which B cells regulate the host neutrophilic response upon exposure to mycobacteria and how neutrophilia may modulate the development of vaccine-induced protective immunity. The data reveal that B cells can regulate neutrophilia during M. tuberculosis infection and BCG vaccination by modulating the IL-17 response. Vaccination studies show that excess neutrophilia adversely affects the development of BCG-elicited Th1 response. These observations suggest that B cells can optimize the development of protective immunity upon BCG vaccination by regulating the IL-17/neutrophilic response. Understanding the mechanisms by which B cells and humoral immunity modulate the immune response during M. tuberculosis infection and BCG immunization, particularly those that regulate IL-17 levels and neutrophilia, may lead to the development of novel strategies for the control of the tubercle bacillus, including efficacious vaccines.