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

Abstract

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-a and its receptors, Fas and FasL and proCaspase 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-a 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. IntroductionDespite vaccination and drug treatment campaigns, tuberculosis (TB) causes an estimated 8-9 million new cases and mortality of 2-3 million deaths annually [1]. The TB epidemic is largely confined to developing countries, and is particularly serious in Sub-Saharan Africa [2], where it is fanned by the HIV epidemic. Despite the high mortality, most infected people do not immediately develop active disease, but become latently infected -though they may later reactivate their disease, if they become immunocompromised [3]. It is thought that perhaps as much as a third of the world's population is latently infected, [4] Eur. J. Immunol. 2010. 40: 291-301 DOI 10.1002 Clinical immunology 291 complicating control efforts by providing a reservoir from which new cases continually arise. Understanding immunity to Mycobacterium tuberculosis, so that more effective vaccines can be developed, is thus an international priority. The response to infection with M. tuberculosis is characterized by a strong inflammatory cell-mediated immune response, with elevated expression of both and . These two cytokines are essential for controlling mycobacterial infections [11][12][13] but in most cases, M. tuberculosis survives to establish a latent infection -which can rapidly reactivate if TNF-a production is blocked [14]. The precise mechanisms involved in this process are still only poorly known. We and others have previously shown that a bias towards IL-4 expression is associated with elevated risk of disease [15] while a bias towards the IL-4 antagonist IL-4d2, or towards IFN-g, is associated with reduced pathology, a better prognosis after infection, recovery after treatment and with ...

Identification of biomarkers for tuberculosis disease using a novel dual-color RT–MLPA assay

“…[9][10][11][12][13][14]17,18 Several biomarkers identified earlier to discriminate between TB cases and LTBIs in German and South African cohorts (for example, FCGR1A (CD64), LTF and RAB33A), 13,19 were confirmed in the current study cohort from the Gambia. Intriguingly, FCGR1A is the only biomarker from our signature that was also identified by a recent large-scale microarray analysis in UK and South-African TB patients, 16 discriminating active TB disease from LTBI, despite being not specific for TB when compared with other inflammatory diseases.…”

“…Two independent dcRT-MLPA assays were performed on whole-blood RNA extracted from five PAXgene tubes collected from 12 Dutch healthy donors at two different time points. Variance component estimation was performed to calculate the contribution of the following four components to the variation in the gene expression profiles: (1) donor variation-the variation within a cohort of healthy individuals, (2) collection variation-the variation within the same healthy individual over time, (3) tube variation-the variation between the five separate PAXgene tubes collected from the same healthy donor, and (4) SPP1, BLR1, CCL19, MMP9, TIMP2), apoptosis-related genes differentially regulated by Mtb (TNFRSF1A, TNFRSF1B, BCL2, CASP8, TNF, FASLG), 14 genes that identify different lymphocyte subsets (CD3E, CD4, CD8A, CD14, CD19, NCAM1), regulatory T-cell-associated markers (FOXP3, IL7R, TGFB1, CTLA4, LAG3, IL10, CCL4, TNFRSF18, IL2RA), effector T-cell markers (IFNG, CXCL10) and reference genes (GAPDH, ABR, GUSB, B2M). Analysis of variance testing for global differences in gene expression profiles indicated significant differences between the study groups (P ¼ 5.4 Â 10 data set revealed profound differences in the overall gene expression profiles between TB cases versus LTBIs and TB cases versus uninfected healthy controls (Pp10…”

Biomarkers for risk of developing active tuberculosis in contacts of TB patients: a prospective cohort study

“…Chemokines such as monocyte chemoattractant protein-1 are suggested to be involved in the massive monocyte recruitment to the lung to control M. tuberculosis infection [36,37]. A role for type I interferons in the accumulation of myeloid cell populations in the lung and pulmonary recruitment of inflammatory monocytes that lead to TB disease immunopathology has also been suggested [38][39][40]. An ongoing infection with an inadequate adaptive immune response against the pathogen may explain the increased percentage of blood monocytes observed in the TB contacts in our study prior to the development of active disease.…”

Modulation of Cell Death byM. tuberculosisas a Strategy for Pathogen Survival

“…The proinflammatory cytokine TNF- α is a crucial component for protection against M. tuberculosis , as shown by the rapid reactivation of latent M. tuberculosis infection in people treated with TNF- α receptor antagonists [89, 90] and the susceptibility of TNF- α -deficient animals to M. tuberculosis [5, 7]. Nonetheless, TNF- α mRNA is elevated in TB patients [4] and in TB/HIV-infected patients elevated levels of TNF- α were associated with necrosis [91]. It has been suggested that while it is essential for protection, that in the presence of elevated levels of IL-4, TNF- α appears to promote tissue damage rather than protection [19, 92], possibly by a cooperative effect of transcription [93, 94].…”

“…Though they are able to control the initial infection, they may later reactivate their disease if they become immunocompromised [3]. Infection with M. tuberculosis is associated with an active inflammatory immune response, characterized by elevated expression of both TNF- α [4–7] and IFN- γ [8–10]. These two cytokines are essential for controlling mycobacterial infections [11–14] but it is clear that in many cases, M. tuberculosis is able to survive this inflammatory process.…”