Latent tuberculosis: mechanisms of host and bacillus that contribute to persistent infection

Most people infected with Mycobacterium tuberculosis contain the initial infection and develop latent tuberculosis. This state is characterised by evidence of an immune response against the bacterium (a positive tuberculin skin test) but no signs of active infection. It can be maintained for the lifetime of the infected person. However, reactivation of latent infection occurs in about 10% of infected individuals, leading to active and contagious tuberculosis. An estimated 2 billion people worldwide are infected with M tuberculosis--an enormous reservoir of potential tuberculosis cases. The establishment and reactivation of latent infection depend on several factors, related to both host and bacterium. Elucidation of the host immune mechanisms that control the initial infection and prevent reactivation has begun. The bacillus is well adapted to the human host and has a range of evasion mechanisms that contribute to its ability to avoid elimination by the immune system and establish a persistent infection. We discuss here current understanding of both host and bacterial factors that contribute to latent and reactivation tuberculosis.     

Rv3615c is a highly immunodominant RD1 (Region of Difference 1)-dependent secreted antigen specific for Mycobacterium tuberculosis infection

The 6-kDa early secretory antigenic target of Mycobacterium tuberculosis (ESAT-6) and the 10-kDa culture filtrate antigen (CFP-10), encoded in region of difference 1 (RD1) and secreted by the ESAT-6 system 1 (Esx-1) secretion system, are the most immunodominant and highly M. tuberculosis (MTB)-specific antigens. These attributes are responsible for their primary importance in tuberculosis (TB) immunodiagnosis and vaccine development. Rv3615c [Esx-1 substrate protein C (EspC)], encoded outside RD1, is similar in size and sequence homology to CFP-10 and ESAT-6, suggesting it might be a target of cellular immunity in TB. Using ex vivo enzyme-linked immunospot- and flow cytometry-based cytokine-secretion assay, we comprehensively assessed cellular immune responses to EspC in patients with active TB, latently infected persons, and uninfected bacillus Calmette-Guérin (BCG)-vaccinated controls. EspC was at least as immunodominant as ESAT-6 and CFP-10 in both active and latent TB infection. EspC contained broadly recognized CD4(+) and CD8(+) epitopes, inducing a predominantly CD4(+) T-cell response that comprised functional T-cell subsets secreting both IFN-γ and IL-2 as well as functional T-cell subsets secreting only IFN-γ. Surprisingly, T-cell responses to EspC were as highly specific (93%) for MTB infection as responses to ESAT-6 and CFP-10, with only 2 of 27 BCG-vaccinated controls responding to each antigen. Using quantitative proteomics and metabolically labeled mutant and genetically complemented MTB strains, we identified the mechanism of the specificity of anti-EspC immunity as the Esx-1 dependence of EspC secretion. The high immunodominance of EspC, equivalent to that of ESAT-6 and CFP-10, makes it a TB vaccine candidate, and its high specificity confers strong potential for T-cell-based immunodiagnosis.     

Recent advances in tuberculosis immunity

Primary tuberculosis infection is acquired by the inhalation of droplets containing Mycobacterium tuberculosis (MTB) bacilli. Only 5-10% of those individuals infected by MTB develop clinical diseases, and disease presentation itself is heterogeneous, suggesting that host factors play a large role in disease susceptibility. Protective immunity in the lung against MTB consist of the innate immunity in which alveolar macrophages play an central role, and the acquired immunity including various type of effector T cells. Recent studies show that the important roles of the receptors which recognize MTB for the development of protective immunity, the difference in the anti-MTB activity of macrophages between human and mice, the macrophage-heterogeneity that affects the anti-MTB activity, the role of IL-10 in the activation of anti-MTB activity of human macrophages, and the role of Th17/IL-17, Th22/ IL-22 and TNF in the protective immunity against human tuberculosis. In this review, these recent advances in tuberculosis immunity will be described.     

结核分枝杆菌感染动物模型概述及研究现状

结核分枝杆菌是引起人类结核的主要病原,由于结核发病机制及由结核分枝杆菌引起的免疫应答机制均未阐明,故迫切需要建立合适的动物结核感染模型作为研究工具。本文仅就动物品系选择、感染途径、感染菌量及模型评判标准等常见问题对已建立的啮齿类动物结核感染模型作简要的比较分析,以反映目前动物结核感染模型研究的现状。     

Intestinal Perforation Due to Mycobacterium tuberculosis in HIV-Infected Individuals: Report of Two Cases

Intestinal perforation is an extremely uncommon complication of Mycobacterium tuberculosis (MTB) infection. We describe two cases of multiple intestinal perforations secondary to MTB in individuals infected with the human immunodeficiency virus (HIV) presenting at the Los Angeles County-University of Southern California Medical Center over a 2-month period. For each case, this was the first presentation of AIDS. One of the two patients had concurrent pulmonary involvement. One patient died, and the other responded to therapy and was discharged in stable condition. The most striking finding in both cases was the extremely large number of acid-fast bacteria seen transmurally on the pathological specimens. This might be related to impaired T-cell function. The resurgence of MTB infection in North America, in the presence of the AIDS epidemic, may result in an increasing frequency of unusual presentations, such as intestinal perforation. Intestinal perforation due to MTB should be considered in HIV-infected patients presenting with an acute abdomen.     

Prolonged survival of scavenger receptor class A-deficient mice from pulmonary Mycobacterium tuberculosis infection

The present study tested the hypothesis that the scavenger receptor SR-A modulates granuloma formation in response to pulmonary infection with Mycobacterium tuberculosis (MTB). To test this hypothesis, we monitored survival and histopathology in WT and SR-A-deficient mice following aerosol infection with MTB Rv. SR-A-deficient (SR-A-/-) mice infected with MTB survived significantly longer than WT mice; the mean survival of SR-A-/- mice exceeded 430 days compared to 230 days for WT mice. Early granuloma formation was not impaired in SR-A-/- mice. The extended survival of SR-A-/- mice was associated with 13- and 3-fold higher number of CD4+ lymphocytes and antigen presenting cells in SR-A-/- lungs compared to WT mice 280 after infection. The histopathology of chronically infected SR-A-/- lungs, however, was marked by abundant cholesterol clefts in parenchymal lesions containing infection in multinucleated giant cells. The present study indicates SR-A as a candidate gene of the innate immune system influencing the chronic phase of M.?tuberculosis infection.     

Increasing CD4+ T cells specific for tuberculosis correlate with improved clinical immunity after highly active antiretroviral therapy

Treatment advances have led to dramatic clinical improvements for patients with HIV-1 infection. These clinical improvements reflect treatment-related improvements in immune function, which are most striking in individuals who develop exaggerated immune inflammatory responses to occult opportunistic infections. The mechanisms accounting for these exaggerated immune responses are unknown. To gain insight into these mechanisms, we intensively studied a subject untreated for disseminated tuberculosis and HIV-1 coinfection who then began treatment for both diseases. We examined the changing frequencies of Mycobacterium tuberculosis (MTB)-specific CD4(+) T cells that produced interferon gamma (IFN-gamma) after short-term stimulation with MTB antigen, and we compared these frequencies with those in HIV-1-seronegative subjects with and without prior exposure to MTB antigens. For the HIV-1/MTB-coinfected subject, the proportion of peripheral blood CD4(+) T cells expressing MTB-specific IFN-gamma was 8.6% at 11 days, 11% at 33 days, and 33% at 95 days after starting treatment for HIV-1. CD4(+) IFN-gamma(+) T cells had a CD45RA(-)CD62L(-) (effector memory) phenotype and most coexpressed interleukin 2. Median frequencies of CD4(+) IFN-gamma(+) T cells from six subjects without and nine subjects with prior exposure to MTB antigens were 0.06 and 0.46%, respectively. We conclude that individuals starting treatment for disseminated tuberculosis and HIV-1 coinfection can accumulate remarkably large numbers of MTB-specific CD4(+) T cells in the peripheral blood. The rapid expansion of antigen-specific effector CD4(+) T cells is one mechanism to explain immediate improvements in clinical immunity after HIV-1 treatment. This mechanism provides a theoretical framework to understand the unusual inflammatory responses recently reported to occur after starting HIV-1 treatment.     

Host genetic factors in resistance and susceptibility to tuberculosis infection and disease

The worldwide public health threat of tuberculosis and the search for novel strategies for preventing and treating disease have focused attention on the interaction between host and pathogen. Despite widespread presence of Mycobacterium tuberculosis, only a relatively small percentage of people exposed to the organism progress to clinical disease. Increasing evidence indicates that host genetic factors influence the outcome of exposure to M. tuberculosis. This evidence is presented here, along with strategies used to identify host genes responsible for resistance/susceptibility in MTB infection. Studies on host genes involved in response to infection by MTB and the relationships between infection and polymorphisms in immune response genes are reviewed. Research on how host genes can influence vaccine responses and the efficacy of drugs or other interventions as well as studies into the relationship of host genes to tuberculosis outcomes may lead to new strategies for prevention and control.     

Aging and immune response in chronic human schistosomiasis

There has been no systematic study of the immune response of individuals over 60 residing in areas endemic for Schistosoma mansoni infection although senescence is reportedly associated with susceptibility to infection and progressive decline in immune function. We have shown previously, in two endemic areas in Minas Gerais, Brazil, that the frequency of individuals over 60 with chronic schistosomiasis is no longer negligible. Several aging-related immunological alterations are already described in medical literature, mostly in the T-cell compartment. Since aging is associated with a decline in T-cell function, it is not surprising that individuals over 60 would be more susceptible to infection. However, not all aged individuals in endemic areas have high intensity of infection; some of them display a negative stool-screening test for the presence of schistosome eggs and low levels of serum antibodies reactive with S. mansoni antigens indicating they are not infected. Non-infected, negative individuals may develop compensatory mechanisms to cope with immune dysfunction and to generate protective responses against the constant threat of infection in these areas. Herein, we reviewed previous reports from our group showing that two mechanisms contribute to distinguish between infected and egg negative aged individuals. First, egg negative aged individuals develop innate immune responses to replace the decline in T-cell function that is observed with aging. Second, chronically activated regulatory T cells, that may impair protective immune responses, are more vigorous in infected aged individuals. We propose that egg negative individuals may be considered as an example of healthy aging in areas endemic for infectious disease.     

Genetic diversity and population structure of Mycobacterium tuberculosis in HIV-1-infected compared with uninfected individuals in Burkina Faso

HIV-1 infection and HIV-1-induced immune deficiency may play a role in selecting particular Mycobacterium tuberculosis (MTB) strains (i.e. genotypes). We compared 43 MTB isolates obtained from HIV-1-infected patients with 77 MTB isolates obtained from HIV-1-uninfected patients in Burkina Faso, by means of DNA fingerprinting methods (MIRU-VNTR plus spoligotyping). This study suggests a lack of structure of the MTB population caused by HIV-1 infection and a similar genetic diversity of MTB in HIV-1-infected compared with uninfected individuals.     

A case for a neonatal, low-dose BCG vaccination trial

The rational design of a successful vaccination strategy against tuberculosis requires certain kinds of information and must take account of several considerations: (i) the nature of the immune response that protects the large majority of individuals infected by Mycobacterium tuberculosis, designated as healthy contacts, must be defined and distinguished from that in tuberculosis patients, whose immune system must have failed; (ii) the vaccination strategy must incorporate a way of priming the immune system to guarantee in all individuals this protective response, normally generated in healthy contacts, upon natural infection by M. tuberculosis; (iii) the strategy must incorporate a mechanism for ensuring that the effectiveness of this priming is not abrogated by exposure to environmental mycobacteria; and (iv) the strategy must take account of the fact that the vaccinated population is genetically heterogeneous, and that individuals will therefore respond variably to most standard vaccination protocols. We describe a tentative proposal for how these interrelated problems might be solved and discuss predictions of this tentative vaccination strategy. Critical testing of the neonatal, low-dose BCG vaccination strategy can only be achieved by a field trial and we outline the considerations underlying this proposal.     

Protective immunity against Mycobacterium tuberculosis

Mycobacterium tuberculosis (MTB) is a facultative intracellular pathogen with which over a billion people have been infected and 3 million people die annually. The bacterium induces vigorous immune responses, yet evades host immunity, persisting within phagosomes of the infected macrophages. Thus, it is necessary to delineate that the virulence-related intracellular survival mechanism and the host immune responses to eradicate M. tuberculosis on the molecular basis. In this regard, recent findings clearly indicated that Toll-like receptors (TLRs) play an essential role in the recognition of MTB components by macrophages and dendritic cells, resulting in not only activation of innate immunity but also development of antigen-specific adaptive immunity. It has been also reported that induction of early death of the infected cells may be one of the strategy of host defense against MTB because macrophages go into apoptosis upon infection with MTB, resulting in suppression of the intracellular replication. Furthermore, recent report has shown that autophagy is induced by IFN-gamma and suppress intracellular survival of mycobacteria, suggesting that activation of autophagy pathway is required to overcome phagosome maturation arrest induced by MTB. In addition, it is known that IFN-gamma plays an important role in protection. The cytokine that is produced from NK cells and dendritic cells at the early period of infection strongly induces not only macrophage activation but also development of antigen-specific IFN-gamma-producing CD4+T cells. Since antigen-specific CD8+ T cells and CD1-restricted T cells are also reported to contribute to the protective immunity, cooperation of these T cells is essential for the host resistance. In this paper, I am going to summarize the recent progress of the understanding of protective immunity against MTB.     

人类免疫缺陷病毒合并结核感染患者外周血Vγ2Vδ2+T淋巴细胞的数量与功能变化

目的 探讨外周血Vγ2Vδ2+T淋巴细胞数与功能变化对HIV合并结核感染状态的影响.方法 将76例HIV/AIDS合并结核感染患者分为活动性结核感染组(HIV+TB组)和潜伏结核感染组(HIV+LTB组).流式细胞仪测定外周血淋巴细胞分类情况.酶联斑点免疫法(ELISPOT)和胞内细胞因子染色(ICS)方法 检测在PPD和磷酸化抗原(HMBPP)的刺激下T淋巴细胞亚群分泌IFN-γ功能的情况.统计学处理采用t检验.结果 HIV+TB组CD3+T淋巴细胞绝对计数(t=-3.67,P<0.01)和Vγ2Vδ2+T淋巴细胞所占CD3+T淋巴细胞比例(t=-2.06,P<0.05)均显著低于HIV+LTB组.PPD刺激时,HIV+LTB组分泌特异性IFN-γ的T淋巴细胞和参与分泌IFN-γ的CD4+T淋巴细胞所占CD3+T淋巴细胞比例,与HIV+TB组比较差异均无统计学意义.HMBPP刺激时,HIV+LTB组与HIV+TB组比较,分泌IFN-γ的特异性T淋巴细胞计数(t=2.71,P<0.01)和产生IFN-7的特异性Vy2'T淋巴细胞比例(t=3.003,P<0.01)均显著增加.结论 Vγ2Vδ2+T淋巴细胞在HIV/AIDS合并活动性结核患者中的数量和功能都有受损,提示该类细胞在CD4+T淋巴细胞受到抑制的情况下可能是人体内抵御结核感染的重要免疫细胞.     

Augmentation of apoptosis and interferon-gamma production at sites of active Mycobacterium tuberculosis infection in human tuberculosis

Pleural tuberculosis (TB) was employed as a model to study T cell apoptosis at sites of active Mycobacterium tuberculosis (MTB) infection in human immunodeficiency virus (HIV)-coinfected (HIV/TB) patients and patients infected with TB alone. Apoptosis in blood and in pleural fluid mononuclear cells and cytokine immunoreactivities in plasma and in pleural fluid were evaluated. T cells were expanded at the site of MTB infection, irrespective of HIV status. Apoptosis of CD4 and non-CD4 T cells in the pleural space occurred in both HIV/TB and TB. Interferon (IFN)-gamma levels were increased in pleural fluid, compared with plasma. Spontaneous apoptosis correlated with specific loss of MTB-reactive, IFN-gamma-producing pleural T cells. Immunoreactivities of molecules potentially involved in apoptosis, such as tumor necrosis factor-alpha, Fas-ligand, and Fas, were increased in pleural fluid, compared with plasma. These data suggest that continued exposure of immunoreactive cells to MTB at sites of infection may initiate a vicious cycle in which immune activation and loss of antigen-responsive T cells occur concomitantly, thus favoring persistence of MTB infection.     

Expression of CCR5 is increased in human monocyte-derived macrophages and alveolar macrophages in the course of in vivo and in vitro Mycobacterium tuberculosis infection.

Human immunodeficiency virus (HIV) replicates more efficiently in Mycobacterium tuberculosis (MTB)-infected macrophages than in uninfected controls. We investigated whether this may be partly explained by changes in expression of CCR5 in the course of mycobacterial infection, as this molecule has been shown to be a coreceptor for HIV entry. Since the lung is the preferential organ of HIV replication in the course of tuberculosis, we preliminarily analyzed beta-chemokine receptor expression in alveolar macrophages from patients with active tuberculosis, using flow cytometry based on an MIP-1alpha ligand-biotin/avidin-FITC detection system. Increased MIP-1alpha receptor (MIP-1alphaR) expression in alveolar macrophages from infected patients was observed whereas no detectable expression could be revealed in uninfected controls. Since MIP-la can also bind CCR1 and CCR4, the presence of CCR5 mRNA was investigated in bronchoalveolar lavage (BAL) cells and detected in alveolar macrophages from tuberculosis patients only. The study was then extended to in vitro MTB-infected macrophages. Monocyte-derived macrophages (MDMs) were left to differentiate for 7 days before MTB H37Rv infection, and CCR5 expression was monitored, by using a specific monoclonal antibody, on days 1, 6, and 11 after infection. Increased CCR5 expression in MTB-infected macrophages was observed, with a peak on day 6 (64% in MTB-infected versus 33% in control cultures) and a decrease by day 11 (25% in MTB infected versus 13% in control cultures). These results show that CCR5 expression is enhanced in the course of in vitro MTB infection and during active pulmonary tuberculosis.     

Correlation expression Toll-like receptor 4 with multidrugs resistant tuberculosis in diabetes mellitus condition

BackgroundToll-like receptor (TLR) are ligand homologous protein in the APC cell membrane that has functions as a receptor to triger leukocytes and innate immune responses. When there is a Microbacterium tuberculosis (MTB) infection enters from droplets to the lungs, the alveolar macrophages perform a phagocytic function. The interaction between M. tuberculosis and the TLR macrophage receptors produces chemokines which induce migration of monocytes and dendrite cells for destruction. Diabetes militus (DM) has become risk factor for developing tuberculosis. DM condition will reduce immunity and the ability of immune cell phagocytes bactery and triger severe infections. The consequences of more severe infection and metabolic disorders that occur make a person more likely to experience Multidrugs resistant MTB. Not much data that reports on the expression of TLR4 as a ligand that triggers an immune response in conditions of MDR and DM. We try to find out correlation between TLR-4 in MDR MTB, diabetes and level of MTB bacteria in experimental animals.MethodsWe conducted an experimental study on 30 experimental mice weighing 25 grams consisting of negative control grub, infected with MTB, infected with MDR MTB, negative control diabetes, MTB DM, MDR MTB DM. DM animals were induced by streptozosin to experience DM, then in the treatment of infection, intraperitoneal MTB and MDR MTB bacterial injections were given. Termination was carried out on day 14. We count number of bacteria level in the lungs and perform evaluation TLR4 from blood sampel.ResultsThe negative control group had mean TLR value of 1.47 (± 0.46) while the MTB group showed an increase in TLR 9.22 (± 0.39) followed by MDR MTB 9.50 (± 0.29), DM negative control 9, 21 (± 0.24) and more increasing in conditions of DM MTB 13.36 (± 0.32) and DM MDR MTB 13.35 (± 0.34). ANOVA analysis showed a significant difference (P = 0.00). pearson correlation analysis find strong correlation TLR4 in MTB and MDR MTB with diabetes.Conclusionthere were a significant difference level TLR4 between MTB and MDR TB infection with diabetes. higher TLR4 level higher in DM MTB, DM MDR MTB. TLR 4 strong correlates with an increase in the number of MTB bacteria.     

Effector functions of heparin-binding hemagglutinin-specific CD8+ T lymphocytes in latent human tuberculosis

BACKGROUND: Most individuals infected with Mycobacterium tuberculosis do not develop tuberculosis (TB) and can be regarded as being protected by an appropriate immune response to the infection. The characterization of the immune responses of individuals with latent TB may thus be helpful in the definition of correlates of protection and the development of new vaccine strategies. The highly protective antigen heparin-binding hemagglutinin (HBHA) induces strong interferon (IFN)- gamma responses during latent, but not active, TB. Because of the recently recognized importance of CD8(+) T lymphocytes in anti-TB immunity, we characterized the CD8(+) T lymphocyte responses to HBHA in subjects with latent TB. RESULTS: HBHA-specific CD8(+) T lymphocytes expressed memory cell markers and synthesized HBHA-specific IFN- gamma . They also restricted mycobacterial growth and expressed cytotoxicity by a granule-dependent mechanism. This activity was associated with the intracellular expression of HBHA-induced perforin. Surprisingly, the perforin-producing CD8(+) T lymphocytes were distinct from the IFN- gamma -producing CD8(+) T lymphocytes. CONCLUSION: During latent TB, the HBHA-specific CD8(+) T lymphocyte population expresses all 3 effector functions associated with CD8(+) T lymphocyte-mediated protective immune mechanisms, which supports the notion that HBHA may be protective in humans and suggests that markers of HBHA-specific CD8(+) T lymphocyte responses may be useful in the monitoring of protection.     

Pulmonary tuberculosis

Pulmonary tuberculosis is a major cause of morbidity and mortality worldwide, resulting in the greatest number of deaths due to any one single infectious agent. This trend is due, at least in part, to increasing numbers of individuals co-infected with HIV and Mycobacterium tuberculosis (MTB). Concerted efforts between the World Health Organization and other agencies, therefore, are underway to improve tuberculosis control worldwide. These include basic research in tuberculosis diagnostics and vaccine development, institution of preventive therapy in individuals dually infected with HIV and MTB, and directly observed short-course antituberculous therapy in developing countries with a high prevalence of MTB infection. Further, newer, longer-acting antituberculous therapeutic agents such as rifapentine, which allow twice-weekly dosing in the continuation phase of anti-MTB therapy, have recently been released and are undergoing clinical trials. This review provides a synopsis of recent developments in these areas and serves as a reference source for interested readers.     

Human splenic macrophages as a model for in vitro infection with Mycobacterium tuberculosis

Macrophages play an important role during Mycobacterium tuberculosis (MTB) infection. In humans most of the studies on MTB-macrophage interactions have been performed using circulating monocytes and monocyte-derived macrophages. However, little research has been performed on this interaction using tissue macrophages. Herein, we used human splenic macrophages to characterize particular responses to MTB infection. Based on morphological, biochemical, and immunological markers, splenic adherent cells exhibit characteristics of tissue macrophages. They were able to efficiently phagocytose both live and heat-killed (h-k) MTB H37Rv. Upon infection with live, but not h-k MTB, an increase in secreted TNF-alpha was elicited. Splenic macrophages produced high basal levels of IL-10; however, infection with live or h-k MTB resulted in decrease IL-10 secretion. Both IL-12p40 and IL-12p70 basal levels were also decreased upon infection with live or h-k MTB; however, while the reduction for IL-12p40 levels was observed at earlier time points (4h) for both live and h-k MTB, infection with live MTB, but not h-k MTB, resulted in a time-dependent secretion of IL-12p40 at 24 and 48h after infection. IL-12p70 levels were completely reduced upon infection by either live or h-k MTB. These results support that human splenic macrophages may represent a potential useful model to study MTB-macrophage interactions in vitro.