Ex Vivo Cytokine mRNA Levels Correlate with Changing Clinical Status of Ethiopian TB Patients and their Contacts Over Time

Abstract

There is an increasing body of evidence which suggests that IL-4 plays a role in the pathogenesis of TB, but a general consensus on its role remains elusive. We have previously published data from a cohort of Ethiopian TB patients, their contacts, and community controls suggesting that enhanced IL-4 production is associated with infection with M. tuberculosis, rather than overt disease and that long-term protection in infected community controls is associated with co-production of the IL-4 antagonist IL-4d2, alongside elevated IL-4. Here, for the first time, we compare data on expression of IFN-γ, IL-4 and IL-4δ2 over time in TB patients and their household contacts. During the follow-up period, the TB patients completed therapy and ceased to display TB-like symptoms. This correlated with a decrease in the relative amount of IL-4 expressed. Over the same period, the clinical status of some of their contacts also changed, with a number developing TB-like symptoms or clinically apparent TB. IL-4 expression was disproportionately increased in this group. The findings support the hypothesis that elevated IL-4 production is generally associated with infection, but that TB disease is associated with a relatively increased expression of IL-4 compared to IFN-γ and IL-4δ2. However, the data also suggest that there are no clear-cut differences between groups: the immune response over time appears to include changes in the expression of IFN-γ, IL-4 and IL-4δ2, and it is the relative, not absolute levels of cytokine expression that are characteristic of clinical status.

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

“…However, it has been suggested that soluble TNFR does not fully explain the effects of TNF-a inhibitors on M. tuberculosis [34,35], and so work into other virulence factors is ongoing. Recent results also suggests that IL-4 (which is associated with poor outcome in human TB) [19] may promote necrosis over apoptosis in M. tuberculosis-infected macrophages (Abebe et al, unpublished data) providing a potential explanation of the observed link between TNF-a, IL-4 and pathological changes [36,37].…”

“…However, it has been suggested that soluble TNFR does not fully explain the effects of TNF-a inhibitors on M. tuberculosis [34,35], and so work into other virulence factors is ongoing. Recent results also suggests that IL-4 (which is associated with poor outcome in human TB) [19] may promote necrosis over apoptosis in M. tuberculosis-infected macrophages (Abebe et al, unpublished data) providing a potential explanation of the observed link between TNF-a, IL-4 and pathological changes [36,37].The goal of this study was therefore to observe what, if any, changes occurred during human TB in the expression of genes for the so-called ''death receptor'' complexes (Fas, FasL, TNF-a and the TNFR1 and TNFR2 receptors), which led to activation of the apoptotic cascade via the Fas-associated death domain protein (FADD) and the pro-apoptotic molecule Caspase 8. We have used RT-PCR to compare the expression of these genes in the peripheral blood of sputum-positive TB patients, their close household contacts and healthy community controls (CC) from Ethiopia, a TB-endemic country.…”

“…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 the ability to maintain the infection in a latent state [16][17][18][19].Thus, the immune response to M. tuberculosis infection appears to be a balance between inflammatory/anti-inflammatory responses in which TNF-a plays an important role. TNF-a is a pleiotropic cytokine, with multiple functions.…”

“…For MACS-separated PBMC, unstimulated leukocytes were lysed immediately after purification and washing in PBS the RNEASY Cell RNA system (Qiagen) according to the manufacturer's instructions. The mRNA was transcribed into cDNA, as previously described [19]. Briefly, cDNA was prepared using the Omniscript reverse transcription kit (Qiagen) with oligo dT primers, according to the manufacturer's instruc- tions, the concentration calculated from the optical density using a GeneQuant spectrophotometer (Amersham Biosciences, Amersham, UK) and stored at À201C until use.…”

Discrimination between Active and Latent Tuberculosis Based on Ratio of Antigen-Specific to Mitogen-Induced IP-10 Production

“…The levels of several cytokines, including interleukin-6 (IL-6), IL-10, IL-15, chemokine (C-X-C) motif ligand (CXCL)/interferon gamma-inducible protein 10 (IP-10), and monocyte chemoattractant protein 2 (MCP-2), were significantly higher in TB patients than in healthy controls (7,11,(18)(19)(20)(21); although these finding suggest important roles for these factors in disease pathogenesis, they are not sufficient for diagnosing active as opposed to latent infections. Several studies have also suggested that biomarker combinations such as IFN-␥Ϫtumor necrosis factor alpha (TNF-␣), IFN-␥ϪIL-2, IFN-␥ϪIL-4, and IL-15ϪMCP-1 might be more sensitive than single markers (18,(22)(23)(24). However, a better biomarker to improve the sensitivity and specificity in discriminating between active TB and LTBI is still needed.…”