Significance of Fas and Fas ligand in tuberculous lymphadenitis

Plasma Levels of sFas-sFasL and FASL Gene Expression Are Associated with Tuberculosis

Apoptosis of macrophages infected by Mycobacterium tuberculosis via Fas-FasL is an important immune mechanism against infection. This study investigated the association of tuberculosis (TB) with the presence of the polymorphisms FAS -670A/G and FASL -124A/G, the levels of sFas and sFasL, and the gene expression of FASL and cytokines. Samples of 200 individuals diagnosed with TB and 200 healthy controls were evaluated. Real-time PCR (genotyping and gene expression) and ELISA (dosages of sFas, sFasL, IFN-γ, and IL-10) tests were performed. There was no association of FAS -670A/G and FASL -124A/G polymorphisms with TB. The TB group exhibited high plasma levels of sFas and reduced plasma levels of sFasL (p < 0.05). The correlation analysis between these markers revealed a positive correlation between the levels of sFas and sFasL, sFasL and FASL expression, and between sFas and FASL expression (p < 0.05). In the TB group, there was a positive correlation between FASL expression and IFN-γ levels and higher levels of IL-10 compared to IFN-γ (p < 0.05). High levels of sFas and reduced levels of sFasL and FASL expression may contribute to the inhibition of apoptosis in infected cells and represent a possible bacterial resistance resource to maintain the infection.

Soluble CD95L in cancers and chronic inflammatory disorders, a new therapeutic target?

Although CD95L (also known as FasL) is still predominantly considered as a death ligand that induces apoptosis in infected and transformed cells, substantial evidence indicate that it can also trigger non-apoptotic signaling pathways whose pathophysiological roles remain to be fully elucidated. The transmembrane ligand CD95L belongs to the tumor necrosis factor (TNF) superfamily. After cleavage by metalloprotease, its soluble form (s-CD95L) fails to trigger the apoptotic program but instead induces signaling pathways promoting the aggressiveness of certain inflammatory disorders such as autoimmune diseases and cancers. We propose to evaluate the various pathologies in which the metalloprotease-cleaved CD95L is accumulated and analyze whether this soluble ligand may play a significant role in the pathology progression. Based on the TNFα-targeting therapeutics, we envision that targeting the soluble form of CD95L may represent a very attractive therapeutic option in the pathologies depicted herein.

Identification of Potential Biomarkers and Related Transcription Factors in Peripheral Blood of Tuberculosis Patients

Tuberculosis (TB), one major threat to humans, can infect one third of the worldwide population, and cause more than one million deaths each year. This study aimed to identify the effective diagnosis and therapy biomarkers of TB. Hence, we analyzed two microarray datasets (GSE54992 and GSE62525) derived from the Gene Expression Omnibus (GEO) database to find the differentially expressed genes (DEGs) of peripheral blood mononuclear cell (PBMC) between TB patients and healthy specimens. Functional and pathway enrichment of the DEGs were analyzed by Metascape database. Protein-protein interaction (PPI) network among the DEGs were constructed by STRING databases and visualized in Cytoscape software. The related transcription factors regulatory network of the DEGs was also constructed. A total of 190 DEGs including 36 up-regulated genes and 154 down-regulated genes were obtained in TB samples. Gene functional enrichment analysis showed that these DEGs were enriched in T cell activation, chemotaxis, leukocyte activation involved in immune response, cytokine secretion, head development, etc. The top six hub genes (namely, LRRK2, FYN, GART, CCR7, CXCR5, and FASLG) and two significant modules were got from PPI network of DEGs. Vital transcriptional factors, such as FoxC1 and GATA2, were discovered with close interaction with these six hub DEGs. By systemic bioinformatic analysis, many DEGs associated with TB were screened, and these identified hub DEGs may be potential biomarkers for diagnosis and treatment of TB in the future.

Cytokine and Chemokine Concentrations as Biomarkers of Feline Mycobacteriosis

Mycobacteriosis is an emerging zoonotic disease of domestic cats and timely, accurate diagnosis is currently challenging. To identify differential cytokine/chemokine concentrations in serum/plasma of cats, which could be diagnostic biomarkers of infection we analysed plasma/serum from 116 mycobacteria-infected cats, 16 healthy controls and six cats hospitalised for unrelated reasons was analysed using the Milliplex MAP Feline Cytokine Magnetic Bead multiplex assay. Three cytokines; sFAS, IL-13 and IL-4 were reduced while seven; GM-CSF, IL-2, PDGF-BB, IL-8, KC, RANTES and TNF-α were elevated in mycobacteria-infected cats compared to healthy controls. However, IL-8 and KC concentrations were not significantly different from cats hospitalised for other reasons. Elevations in TNF-α and PDGF-BB may have potential to identify M. bovis and M. microti infected cats specifically while GM-CSF, IL-2 and FLT3L were increased in MTBC infected cats. This study demonstrates potential use of feline tuberculosis as a spontaneously occurring model of this significant human disease. Cytokine profiling has clear diagnostic potential for mycobacteriosis of cats and could be used discriminate tuberculous from non-tuberculous disease to rapidly inform on zoonotic risk. Future work should focus on the in-field utility of these findings to establish diagnostic sensitivity and specificity of these markers.

Gene expression and TB pathogenesis in rhesus macaques: TR4, CD40, CD40L, FAS (CD95), and TNF are host genetic markers in peripheral blood mononuclear cells that are associated with severity of TB lesions

Tuberculosis (TB) pathologic lesions in rhesus macaques resemble those in humans. The expression levels of several host TB candidate genes in the peripheral blood mononuclear cells (PBMCs) of six rhesus macaques experimentally infected with Mycobacterium tuberculosis were quantified pre-infection and at several dates post-infection. Quantitative measures of TB histopathology in the lungs including: granuloma count, granuloma size, volume of granulomatous and non-granulomatous lesions, and direct bacterial load, were used as the outcomes of a multi-level Bayesian regression model in which expression levels of host genes at various dates were used as predictors. The results indicate that the expression levels of TR4, CD40, CD40L, FAS (CD95) and TNF in PBMC were associated with quantitative measures of the severity of TB histopathologic lesions in the lungs of the study animals. Moreover, no reliable association between the expression levels of IFNE in PBMCs and the severity of TB lesions in the lungs of the study animals was found. In conclusion, PBMC expression profiles derived from the above-listed host genes might be appropriate biomarkers for probabilistic diagnosis and/or prognosis of TB severity in rhesus macaques.

Immunotherapy for TB

Mycobacterium tuberculosis was one of the first human pathogens to be identified as the cause of a specific disease – TB. TB was also one of the first specific diseases for which immunotherapy was attempted. In more than a century since, multiple different immunotherapies have been attempted, alongside vaccination and antibiotic treatment, with varying degrees of success. Despite this, TB remains a major worldwide health problem that causes nearly 2 million deaths annually and has infected an estimated 2 billion people. A major reason for this is that M. tuberculosis is an ancient human pathogen that has evolved complex strategies for persistence in the human host. It has thus been long understood that, to effectively control TB, we will need to address the ability of the pathogen to establish a persistent, latent infection in most infected individuals. This review discusses what is presently known about the interaction of M. tuberculosis with the immune system, and how this knowledge has been used to design immunotherapeutic strategies.

Modulation of cell death by M. tuberculosis as a strategy for pathogen survival

It has been clearly demonstrated that in vitro, virulent M. tuberculosis can favor necrosis over apoptosis in infected macrophages, and this has been suggested as a mechanism for evading the host immune response. We recently reported that an effect consistent with this hypothesis could be observed in cells from the blood of TB patients, and in this paper, we review what is known about evasion strategies employed by M. tuberculosis and in particular consider the possible interaction of the apoptosis-inhibiting effects of M. tuberculosis infection with another factor (IL-4) whose expression is thought to play a role in the failure to control M. tuberculosis infection. It has been noted that IL-4 may exacerbate TNF-α-induced pathology, though the mechanism remains unexplained. Since pathology in TB typically involves inflammatory aggregates around infected cells, where TNF-α plays an important role, we predicted that IL-4 would inhibit the ability of cells to remove M. tuberculosis by apoptosis of infected cells, through the extrinsic pathway, which is activated by TNF-α. Infection of human monocytic cells with mycobacteria in vitro, in the presence of IL-4, appears to promote necrosis over apoptosis in infected cells—a finding consistent with its suggested role as a factor in pathology during M. tuberculosis infection.

Expression of apoptosis-related genes in an Ethiopian cohort study correlates with tuberculosis clinical status

Mycobacterium tuberculosis remains one of the world's deadliest pathogens in part because of its ability to persist in the face of an active immune response. It has been suggested that apoptosis of infected macrophages is one way in which the host deals with intracellular pathogens and that M. tuberculosis can inhibit this process. To assess the relevance of this process for human disease, we compared the expression of multiple genes involved in the activation of the extrinsic ("death receptor initiated") pathway of apoptosis in 29 tuberculosis patients, 70 tuberculosis contacts and 27 community controls from Ethiopia. We found that there is a strong upregulation of genes for factors that promote apoptosis in PBMC from individuals with active disease, including TNF-alpha and its receptors, Fas and FasL and pro-Caspase 8. The anti-apoptotic factor FLIP, however, was also upregulated. A possible explanation for this dichotomy was given by fractionation of PBMC using CD14, which suggests that macrophage/monocytes may regulate several key molecules differently from non-monocytic cells (especially TNF-alpha and its receptors, a finding confirmed by protein ELISA) potentially reducing the sensitivity to apoptotic death of monocyte/macrophages--the primary host cell for M. tuberculosis. This may represent an important survival strategy for the pathogen.

Interaction of Mycobacterium tuberculosis with the host: consequences for vaccine development

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), remains a major worldwide health problem that causes more than 2 million deaths annually. In addition, an estimated 2 billion people are latently infected with M. tuberculosis. The bacterium is one of the oldest human pathogens and has evolved complex strategies for survival. Therefore, to be successful in the high endemic regions, any future TB vaccine strategy will have to be tailored in accordance with the resulting complexity of the TB infection and anti-mycobacterial immune response. In this review, we will discuss what is presently known about the interaction of M. tuberculosis with the immune system, and how this knowledge is used in new and more advanced vaccine strategies.

Differential expression of mycobacterial antigen MPT64, apoptosis and inflammatory markers in multinucleated giant cells and epithelioid cells in granulomas caused by Mycobacterium tuberculosis

The development of granulomas is a major histopathological feature of tuberculosis. Very little information is available concerning the physiology and functions of different cell types in the tuberculous granulomas. The aim of this study was to compare the epithelioid cells (ECs) and multinucleated giant cells (MGCs) in the granulomas caused by Mycobacterium tuberculosis complex organisms. Lymph node biopsies from 30 cases of lymphadenitis were studied for expression of the secreted mycobacterial protein MPT64, caspase 3 as a marker of apoptosis, apoptosis-related proteins (Fas Ligand, Fas and Bax) and inflammatory cytokines (interleukin-10, transforming growth factor-β (TGF-β), tumour necrosis factor-α and interferon-γ) by immunohistochemistry. MGCs more often contained M. tuberculosis secretory antigen MPT64 (p < 0.001) and expressed more TGF-β (p = 0.004) than ECs. The total number of apoptotic MGCs was higher than the number of apoptotic ECs (p = 0.04). Interestingly, there was a significant negative correlation between apoptosis and MPT64 expression in MGCs (r = −0.569, p = 0.003), but not in ECs, implying that the heavy antigen load would lead to inhibition of apoptosis in these cells. When compared with ECs, higher percentage of MGCs expressed Fas Ligand and Fas (p < 0.004). The role of MGCs may thus be different from surrounding ECs and these cells by virtue of higher mycobacterial antigen load, more TGF-β and reduced apoptosis may contribute towards persistence of infection.

Vaccine Approaches to Prevent Tuberculosis

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is one of the main killers among infectious pathogens in the world and represents an important factor that sustain poverty in developing countries. Failure of the BCG vaccine to protect in endemic regions, and increasing problems with multi-drug-resistant TB calls for development of better vaccines to prevent reactivation of tuberculosis. It has been estimated that an effective post-exposure vaccine will prevent 30-40% of the TB cases. New vaccines should also prevent development of TB in HIV-infected individuals. Recent characterization of M. tuberculosis H37Rv by proteomic methods has revealed a large number of novel secreted proteins that should be investigated in mouse models for latent and slowly progressive TB. There is an important balance between control of infection and tissue destruction in TB, and M. tuberculosis has developed strategies to prevent immune-mediated sterilization. Central to this strategy is inhibition of apoptosis of macrophages. Development of novel vaccines should therefore take into consideration the effects on central markers to obtain a better picture of regulation of immunity, including FasL and Bcl-2 which are essential in regulation of apoptosis.

Immunohistochemical analysis of cytokines and apoptosis in tuberculous lymphadenitis

Relatively little is known about the effector mechanisms whereby the human immune system controls Mycobacterium tuberculosis infection. In this study we elaborate on the immune response and mechanisms of persistence of mycobacteria in lesions by analysing, using immunohistochemistry, the expression of cytokines [tumour necrosis factor-alpha (TNF-alpha), interleukin-10 (IL-10), transforming growth factor-beta (TGF-beta) and interferon-gamma (IFN-gamma)], apoptotic cells and apoptosis-related proteins [Bcl2, Bax, Fas ligand (FasL) and Fas] in the human tuberculous lymphadenitis lesions. The expression of apoptosis-related proteins has been shown to be exploited by mycobacteria to evade the immune response and persist in the host. Foreign body (FB) granulomas were used as controls. In tuberculosis (TB) granulomas, epithelioid cells and multinucleated giant cells expressed cytokines differently. In epithelioid cells, the numbers of TNF-alpha-, IL-10- and TGF-beta-stained cells were higher than IFN-gamma-stained cells (P < 0.01). TGF-beta and FasL were strongly expressed in the necrotic centres as compared with other cytokines. More giant cells expressed IL-10 and TGF-beta than expressed TNF-alpha and IFN-gamma (P < 0.01). Staining of consecutive sections revealed that some giant cells expressed IL-10 but not TNF-alpha. Apoptotic TB giant cells correlated positively with the expression of TNF-alpha, IFN-gamma and TGF-beta, but not with the expression of IL-10. The percentage of giant cells expressing Bax was lower than those expressing Fas, unlike the epithelioid cells, suggesting that TB giant cells are less susceptible to apoptosis. Compared with FB giant cells, there were fewer TB giant cells showing TNF-alpha, IFN-gamma, FasL, Fas expression or undergoing apoptosis (P < 0.05). Taken together, these observations show that the cellular microenvironment of TB granulomas down-regulates microbicidal functions, favouring bacillary survival and persistence. TGF-beta and FasL may be responsible for tissue destruction. The giant cells, being less susceptible to apoptosis, may remain a continuous source of pro-inflammatory cytokines, causing immune pathology.