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Keertan Dheda

Publications and source records attributed to Keertan Dheda.

At least 19 recordsLinked to original sources
PubMed2006

The stability of mRNA encoding IL-4 is increased in pulmonary tuberculosis, while stability of mRNA encoding the antagonistic splice variant, IL-4delta2, is not.

The prototype Th2 cytokine IL-4, and its competitive antagonist IL-4delta2, may be important determinants of outcome in human tuberculosis (TB). However, there are no data on how gene expression of these cytokines is regulated. To evaluate this the stability of IL-4 and IL-4delta2 mRNA after the addition of actinomycin-D, was evaluated in whole blood from subjects with pulmonary TB and uninfected healthy volunteers. The Th2/Th1 (IL-4/IFN-gamma) mRNA ratio in unstimulated cells in whole blood was significantly greater in TB subjects than in controls (p<0.05). The mRNA half-life of the agonist (IL-4), but not the antagonist (IL-4delta2), was significantly prolonged in subjects with TB compared to healthy volunteers ( approximately 5-fold, p=0.0016), and the IL-4/IL-4delta2 ratio was higher in TB patients compared to controls (p<0.05). The differential stability of the Th2 agonist, IL-4, compared to the antagonist IL-4delta2, represents a hitherto undescribed post-transcriptional regulatory mechanism that may modulate the polarisation of Th1/Th2 responses in human TB.

Adult↗
PubMed2006

Expression of IL-4 mRNA in peripheral blood mononuclear cells from normal donors in relation to expression of TLR2.

When IL-4 mRNA was distinguished from mRNA encoding its antagonist, the splice variant IL-4delta2, it was found to correlate directly with expression of TLR2 in fresh peripheral blood mononuclear cells (PBMCs) from normal donors (p=0.0013). Similarly IL-4 mRNA was high when TLR2 mRNA was abundant compared to levels of mRNA encoding its heterodimerisation partners TLR1 (p=0.0007) or TLR6 (p=0.0007). IL-4delta2 tended to show the reverse effect; IL-4delta2 mRNA was high when TLR2 was low relative to TLR1 (p=0.001). When subpopulations of the PBMCs were examined these relationships were found to be restricted to the CD3+ cells. The CD3+ cell population from 5 of 10 donors had detectable TLR2 mRNA. When levels of TLR1, IL-4 and IFN-gamma mRNA were assayed in the TLR2(low) and TLR2(high) CD3+ cells, it was found that IL-4 mRNA was restricted to the TLR2(high) T cells (p=0.007) while TLR1 was higher in the TLR2(low) T cells (p=0.015). IFN-gamma was also somewhat increased in the TLR2(low) (ns). None of these correlations with TLR mRNA expression levels were found in similar samples from tuberculosis patients, or when similar analyses were performed with data for IL-10 mRNA in cells from the same donors. We conclude that in T cell populations from normal donors, expression of IL-4 (but not of its antagonist, IL-4delta2, or of IL-10) is associated with high TLR2 and low TLR1.

Alternative Splicing↗
PubMed2006

Persistently elevated T cell interferon-gamma responses after treatment for latent tuberculosis infection among health care workers in India: a preliminary report.

BACKGROUND: T cell-based interferon-gamma (IFN-gamma) release assays (IGRAs) are novel tests for latent tuberculosis infection (LTBI). It has been suggested that T cell responses may be correlated with bacterial burden and, therefore, IGRAs may have a role in monitoring treatment response. We investigated IFN-gamma responses to specific TB antigens among Indian health care workers (HCWs) before, and after LTBI preventive therapy. METHODS: In 2004, we established a cohort of HCWs who underwent tuberculin skin testing (TST) and a whole-blood IGRA (QuantiFERON-TB-Gold In-Tube [QFT-G], Cellestis Ltd, Victoria, Australia) at a rural hospital in India. HCWs positive by either test were offered 6 months of isoniazid (INH) preventive therapy. Among the HCWs who underwent therapy, we prospectively followed-up 10 nursing students who were positive by both tests at baseline. The QFT-G assay was repeated 4 and 10 months after INH treatment completion (i.e. approximately 12 months and 18 months after the initial testing). IFN-gamma responses to ESAT-6, CFP-10 and TB7.7 peptides were measured using ELISA, and IFN-gamma >/=0.35 IU/mL was used to define a positive QFT-G test result. RESULTS: All participants (N = 10) reported direct contact with smear-positive TB patients at baseline, during and after LTBI treatment. All participants except one started treatment with high baseline IFN-gamma responses (median 10.0 IU/mL). The second QFT-G was positive in 9 of 10 participants, but IFN-gamma responses had declined (median 5.0 IU/mL); however, this difference was not significant (P = 0.10). The third QFT-G assay continued to be positive in 9 of 10 participants, with persistently elevated IFN-gamma responses (median 7.9 IU/mL; P = 0.32 for difference against baseline average). CONCLUSION: In an environment with ongoing, intensive nosocomial exposure, HCWs had strong IFN-gamma responses at baseline, and continued to have persistently elevated responses, despite LTBI treatment. It is plausible that persistence of infection and/or re-infection might account for this phenomenon. Our preliminary findings need confirmation in larger studies in high transmission settings. Specifically, research is needed to study T cell kinetics during LTBI treatment, and determine the effect of recurrent exposures on host cellular immune responses.

Journal Article↗
PubMed2006

Myobacterium tuberculosis induces selective up-regulation of TLRs in the mononuclear leukocytes of patients with active pulmonary tuberculosis.

Human and mouse studies indicate that TLRs are important in mycobacterial infections. We investigated TLR gene expression in fresh unstimulated blood and bronchoalveolar lavage from patients with pulmonary tuberculosis using a well-validated, real-time PCR. A human splice variant of TLR1, designated hsTLR1, was found in all donors tested. hsTLR1 mRNA lacks exon 2, which is a 77-bp region of the 5'-untranslated region, but contains the same coding sequence as TLR1. Compared with the matched controls, whole blood from patients had increased levels of mRNA encoding TLR2 (p = 0.0006), TLR1 (p = 0.004), hsTLR1 (p = 0.0003), TLR6 (p < 0.0001), and TLR4 (p = 0.0002). By contrast, expression of these TLRs was not increased in bronchoalveolar lavage. An increased level of hsTLR1 mRNA was found in both CD3- (p = 0.0078) and CD4+ cells (p = 0.028), resulting in an increased ratio of hsTLR1 mRNA to TLR1 and to TLR6 mRNA. An in vitro study in THP1 cells suggested that this relative increase in hsTLR1 might be attributable to a direct effect of mycobacterial components because it could be mimicked by mycobacterial preparations in the absence of IFN-gamma or T cells and by the TLR1/2 agonist Pam3CysK4. Half-life studies using blood from patients with pulmonary tuberculosis and THP1 cells exposed to Myobacterium tuberculosis in vitro showed p38 MAPK-independent stabilization of mRNAs encoding hsTLR1 and TLR1. We conclude that M. tuberculosis exerts direct effects on patterns of TLR expression, partly via changes in mRNA half-life. The significance of these changes in the pathogenesis of disease deserves further investigation.

Alternative Splicing↗
PubMed2006

Immune systems in developed and developing countries; implications for the design of vaccines that will work where BCG does not.

New vaccine candidates for tuberculosis are beginning to enter clinical trials. In this review we discuss issues surrounding the design of these candidates, and the way they were screened in animal models. First, screening vaccines for their ability to attenuate inevitably fatal tuberculosis in immunologically naïve mice might be leading to the selection of inappropriate candidates. We need to screen vaccines for their ability to stop the development of progressive disease, since this is what they must achieve in man. A solution to this problem is proposed. Secondly, we point out that some mouse models of tuberculosis in laboratories in developing countries, where exposure to environmental mycobacteria is large, mimic neglected aspects of human disease more closely than do low-dose infections in hyper-susceptible immunologically naïve mice in the USA or Europe. We need to think more about geographical differences in immunological experience, and these mouse models can help us. Thirdly, we conclude that in developing countries where BCG fails this is not because there is too little Th1 response, but rather because the Th1 response is rendered ineffective and immunopathological by other subversive mechanisms, including IL-4 responses and inappropriate regulatory T cell function. Therefore, we suggest that vaccines that will work in those countries might need to have immunoregulatory properties that can switch off pre-existing subversive mechanisms, and block their development in the future. The development of such vaccines, that might work where BCG does not, will require a greater understanding of the roles of the many types of regulatory T cell in tuberculosis.

Animals↗
PubMed2006

New tools and emerging technologies for the diagnosis of tuberculosis: part I. Latent tuberculosis.

Nearly a third of the world's population is estimated to be infected with Mycobacterium tuberculosis. This enormous pool of latently infected individuals poses a major hurdle for global tuberculosis (TB) control. Currently, diagnosis of latent TB infection (LTBI) relies on the tuberculin skin test (TST), a century-old test with known limitations. In this review, the first of a two-part series on new tools for TB diagnosis, recent advances in the diagnosis of LTBI are described. The biggest advance in recent years has been the development of in vitro T-cell-based interferon-gamma release assays (IGRAs) that use antigens more specific to M. tuberculosis than the purified protein derivative used in the TST. Available research evidence on IGRAs suggests they have higher specificity than TST, better correlation with surrogate markers of exposure to M. tuberculosis in low-incidence settings, and less cross-reactivity due to BCG vaccination than the TST. IGRAs also appear to be at least as sensitive as the purified protein derivative-based TST for active TB. In the absence of a gold standard for LTBI, sensitivity and specificity for LTBI are not well defined. Besides high specificity, other potential advantages of IGRAs include logistical convenience, avoidance of poorly reproducible measurements, such as skin induration, need for fewer patient visits and the ability to perform serial testing without inducing the boosting phenomenon. Overall, due to its high specificity, IGRAs may be useful in low-endemic, high-income settings where cross-reactivity due to BCG might adversely impact the utility of TST. However, despite the growing evidence supporting the use of IGRAs, several unresolved and unexplained issues remain. The review concludes by highlighting areas where evidence is lacking, and provides an agenda for future research. Active TB and drug resistance are discussed in Part II; 423-432 of this issue.

Antigens, Bacterial↗
PubMed2006

New tools and emerging technologies for the diagnosis of tuberculosis: part II. Active tuberculosis and drug resistance.

Tuberculosis (TB) is one of the world's most important infectious causes of morbidity and mortality among adults. Between 8 and 9 million develop TB disease, and approximately 2 million die from TB each year. Despite this enormous global burden, case detection rates are low, posing major hurdles for TB control. Conventional TB diagnosis continues to rely on smear microscopy, culture and chest radiography. These tests have known limitations. Conventional tests for detection of drug resistance are slow, tedious and difficult to perform in field conditions. This second half of a two-part review series on new tools for TB diagnosis describes recent advances and emerging technologies in the diagnosis of active disease, and detection of drug resistance. For diagnosis, new tools include newer versions of nucleic acid amplification tests, immune-based assays, skin patch test and rapid culture systems. For drug resistance, new tools include line-probe assays, bacteriophage-based assays, molecular beacons and microscopic observation drug susceptibility assay. Although the ideal test for TB is still not in sight, substantial progress has been made in the past decade. With the resurgence of interest in the development of new tools for TB control, it is likely that the next decade will see greater progress and tangible benefits. However, the challenge will be to ensure that new tools undergo rigorous evaluations in field conditions, and also to make sure that benefits of promising new tools actually reach the populations in developing countries that need them most. Latent TB is discussed in Part I; 413-422 of this issue.

Antigens, Bacterial↗
PubMed2005

Performance of a T-cell-based diagnostic test for tuberculosis infection in HIV-infected individuals is independent of CD4 cell count.

The performance characteristics of the enzyme-linked immunospot assay (ELISPOT) assay (T-SPOT TB) for the diagnosis of latent tuberculosis infection in HIV-infected individuals are unknown. Given that ELISPOT enumerates Mycobacterium tuberculosis antigen-specific IFN-gamma-secreting T cells, HIV-associated immunosuppression might adversely affect test performance. However, we found that 28 out of 29 HIV-positive individuals (97%) gave evaluable test results, and performance was independent of the CD4 T-cell count. ELISPOT test performance appears to be independent of HIV-associated immunosuppression.

Adult↗
PubMed2005

Expression of a novel cytokine, IL-4delta2, in HIV and HIV-tuberculosis co-infection.

BACKGROUND: Correcting the Th2 shift in HIV/AIDS represents a potential intervention strategy. However data on interleukin (IL)-4 expression in HIV or AIDS are un-interpretable because of failure to distinguish between IL-4 and its splice variant and natural antagonist, IL-4delta2. OBJECTIVE: To determine Th1 [interferon (IFN)-gamma], IL-4delta2 and Th2 (IL-4) expression in whole blood and lung lavage from healthy volunteers and in HIV or HIV-tuberculosis (TB) co-infection. DESIGN: Cross-sectional with prospective cohort. METHODS: Expression of IL-4delta2, IL-4 and IFN-gamma were determined by quantitative real-time PCR, using unstimulated cells from whole blood and lung lavage, in 20 HIV-TB (pulmonary) co-infected patients, 20 matched HIV-positive controls and 20 HIV-negative healthy volunteers. Results were correlated with plasma viral load, CD4 cell counts, radiological scores and response to anti-TB treatment. RESULTS: Compared to HIV negative donors, stable HIV-positive donors did not have increased levels of mRNA encoding IL-4, IL-4delta2 or IFN-gamma in blood or lavage. By contrast, the HIV-TB co-infected donors had increased IL-4 and IFN-gamma in both compartments. However the antagonist, IL-4delta2 was increased only in lavage. Consequently the dominant form was IL-4delta2 in lavage, but IL-4 itself in blood. The lung IL-4/IFN-gamma ratio correlated with radiological disease extent. With anti-TB treatment, IL-4 levels did not change whilst IL-4delta2 levels increased significantly. CONCLUSIONS: IL-4 and its natural antagonist, IL-4delta2 and are not upregulated in the absence of opportunistic infection. However in HIV-TB co-infection both cytokines increase in lung, but only IL-4 in the periphery. Further studies are required to determine if IL-4 facilitates systemic HIV progression.

AIDS-Related Opportunistic Infections↗
PubMed2005

Lung remodeling in pulmonary tuberculosis.

Tuberculosis is a global public health catastrophe responsible for >8 million cases of illness and 2 million deaths annually. Pulmonary cavitation with cough-generated aerosol is the principle means of spread, and lung remodeling (healed cavitation, fibrosis, and bronchiectasis) is a major cause of lung disability, surpassing all other diffuse parenchymal lung diseases combined. Efficient granuloma turnover is mycobactericidal, and extracellular matrix is disbanded without scarring. In many with progressive disease, however, there is dysregulated granuloma turnover, liquefactive necrosis, and pathological scarring. The pathological mechanisms and the related immunological pathways underpinning these phenomena are reviewed in the present article. Further studies are needed to identify and develop specific immunotherapeutic interventions that target immunopathology, since they have the potential to substantially reduce spread.

Humans↗
PubMed2005

In vivo and in vitro studies of a novel cytokine, interleukin 4delta2, in pulmonary tuberculosis.

RATIONALE: Tuberculosis progresses despite potent Th1 responses. A putative explanation is the simultaneous presence of a subversive Th2 response. However, interpretation is confounded by interleukin 4delta2 (IL-4delta2), a splice variant and inhibitor of IL-4. OBJECTIVE: To study levels of mRNA encoding IL-4 and IL-4delta2, and their relationship to treatment and clinical parameters, in cells from lung lavage and blood from patients with pulmonary tuberculosis. METHODS: IL-4delta2, IFN-gamma, IL-4, and soluble CD30 (sCD30) levels were measured by polymerase chain reaction and relevant immunoassays in 29 patients and matched control subjects lacking responses to tuberculosis-specific antigens. RESULTS: mRNA levels for IL-4 and IL-4delta2 were elevated in unstimulated cells from blood and lung lavage of patients versus control subjects (p < 0.005). In control subjects, there were low basal levels of IL-4 and IL-4delta2 mRNA expressed mainly by non-T cells (p < 0.05). However, in patients, there were greater levels of mRNA for both cytokines in both T- and non-T-cell populations (p < 0.05 compared with control subjects). Radiologic disease correlated with the IL-4/IFN-gamma ratio and sCD30 (p < 0.005). After chemotherapy, IL-4 mRNA levels remained unchanged, whereas IL-4delta2 increased in parallel with IFN-gamma (p < 0.05). Sonicates of Mycobacterium tuberculosis upregulated expression of IL-4 relative to IL-4delta2 in mononuclear cell cultures from patients (p < 0.05). CONCLUSIONS: A Th2-like response, prominent in T cells and driven by tuberculosis antigen, is present in tuberculosis and modulated by treatment, suggesting a role for IL-4 and IL-4delta2 in the pathogenesis of tuberculosis and their ratio as a possible marker of disease activity. The specific antigens inducing the IL-4 response require identification to facilitate future vaccine development strategies.

Adult↗
PubMed2005

Do successful tuberculosis vaccines need to be immunoregulatory rather than merely Th1-boosting?

Tuberculosis vaccine candidates are entering clinical studies in areas where BCG fails. This is a high-risk strategy. We suggest that geographical variation in the efficacy of BCG is related to the presence in developing countries of a cross-reactive background Th2-like response, probably attributable to exposure of mother and infant to helminths and environmental mycobacteria. Such Th2-like activity can stop Mycobacterium tuberculosis from being pushed into a latent state by the Th1 response, impair bactericidal functions and cause toxicity of TNF-alpha and pulmonary fibrosis. A successful vaccine, rather than driving a Th1 response, might need to suppress this pre-existing subversive Th2-like component.

Animals↗
PubMed2005

Immune responses to tuberculosis in developing countries: implications for new vaccines.

Tuberculosis is out of control in developing countries, where it is killing millions of people every year. In these areas, the present vaccine - Mycobacterium bovis bacillus Calmette-Guérin (BCG) - is failing. Progressive tuberculosis occurs because the potentially protective T helper 1 (T(H)1)-cell response is converted to an immunopathological response that fails to eliminate the bacteria. Here, we discuss the data indicating that the problem in developing countries is not a lack of adequate T(H)1-cell responses but, instead, an exaggerated tendency to switch to immunopathological responses. We propose that a successful vaccine needs to block this immunopathology, because it is not the quantity of T(H)1-cell activity that matters but, rather, its context.

Antibodies, Bacterial↗
PubMed2005

Utility of the antigen-specific interferon-gamma assay for the management of tuberculosis.

PURPOSE OF REVIEW: The tuberculin skin test, now over a century old, is prone to reader variability, and outcomes are influenced by cross-reactivity with environmental mycobacteria, previous bacillus Calmette-Guerin (BCG) vaccination, and anergy in immunosuppressed individuals. More recently, T-cell-based interferon-gamma responses to Mycobacterium tuberculosis - specific antigens have been investigated for their role in diagnosing latent tuberculosis infection. RECENT FINDINGS: We review the evidence supporting the utility of the interferon-gamma assay for the diagnosis of latent tuberculosis infection (LTBI) in low-prevalence countries. We discuss the principle of the test, technical factors related to performance, and its utility in active tuberculosis, in specialised subgroups such as immunocompromised patients, and its applicability in developing countries. SUMMARY: Compared with the tuberculin skin test, the antigen-specific interferon-gamma assay, when used in a standardised protocol (overnight incubation assay using a combination of two antigens) for the diagnosis of LTBI, has greater specificity in BCG-vaccinated individuals, displays a stronger association with exposure, and is less biased by environmental mycobacteria such as Mycobacterium avium. Prospective studies are required, however, to confirm that treating LTBI, as defined by the interferon-gamma assay, will reduce the tuberculosis burden in low-prevalence countries and whether interferon-gamma responses are predictive of those who have a high risk of progression to active tuberculosis. Further studies are required to address the utility of the interferon-gamma assay in specialised subgroups of patients, in developing countries, and as a marker of disease activity.

Adult↗
PubMed2004

Outcome of HIV-associated tuberculosis in the era of highly active antiretroviral therapy.

BACKGROUND: The benefit of highly active antiretroviral therapy (HAART) in the treatment of patients coinfected with tuberculosis (TB) and human immunodeficiency virus (HIV) is unclear because of concerns about treatment-related complications. METHODS: We compared outcomes in patients starting TB treatment during the pre-HAART era (before 1996; n=36) with those in patients starting treatment during the HAART era (during or after 1996; n=60). RESULTS: During a median of 3.6 years of follow-up, 49 patients died or had an AIDS event. Compared with patients in the pre-HAART group, those in the HAART group had a lower risk of death (cumulative at 4 years, 43% vs. 22%; P=.012) and of death or having an AIDS event (69% vs. 43%; P=.023). Event risk within the first 2 months of TB treatment was exceptionally high in patients with CD4(+) cell counts <100 cells/mm(3) and declined thereafter. HAART use during follow-up was associated with a marked reduction in event risk (adjusted hazard ratio, 0.38 [95% confidence interval, 0.16-0.91]). CONCLUSIONS: HAART substantially reduces new AIDS events and death in coinfected patients. Those with a CD4(+) cell count <100 cells/mm(3) have a high event risk during the intensive phase of anti-TB treatment. These data should be taken into account when deciding to delay HAART in coinfected patients with CD4(+) cell counts <100 cells/mm(3).

AIDS-Related Opportunistic Infections↗