Bactericidal Activity in Whole Blood As a Potential Surrogate Marker of Immunity After Vaccination Against Tuberculosis

Clinical and Diagnostic Laboratory Immunology. Jul, 2002  |  Pubmed ID: 12093693

The development of new tuberculosis (TB) vaccines will require the identification of correlates of human protection. This study examined the balance between immunity and virulence in a whole blood infection model in which intracellular mycobacterial survival was measured using BACTEC. In the blood of tuberculin-negative donors, counts of Mycobacterium tuberculosis H(37)Ra organisms fell by 0.14 log(10) CFU during 96 h of whole blood culture, whereas counts of Mycobacterium bovis BCG, M. tuberculosis H(37)Rv, and a clinical TB isolate's organisms increased by 0.13, 0.43, and 1.04 log(10) CFU, respectively (P < 0.001), consistent with their relative virulence. Inhibition of tumor necrosis factor alpha by the addition of methylprednisolone or pentoxifylline or removal of CD4(+) or CD8(+) T cells by magnetic beads had deleterious effects on immune control of intracellular growth only in the blood of tuberculin-positive donors. Repeated vaccination of eight tuberculin-negative volunteers with M. bovis BCG resulted in a 0.3 log (50%) reduction in BCG CFU counts in the model compared to baseline values (P < 0.05). Three of the volunteers responded only after the second vaccination. These experiments indicate that whole blood culture may be used to measure immunity to M. tuberculosis and that further studies of repeated BCG vaccination are warranted.

Investigation of the Relationships Between Immune-mediated Inhibition of Mycobacterial Growth and Other Potential Surrogate Markers of Protective Mycobacterium Tuberculosis Immunity

The Journal of Infectious Diseases. Nov, 2002  |  Pubmed ID: 12404160

Tuberculosis (TB) vaccine development is hindered by the lack of clear surrogate markers of protective human immunity to Mycobacterium tuberculosis. This study evaluated the hypothesis that immune-mediated inhibition of mycobacterial growth would more directly correlate with protective TB immunity than other immunologic responses. Bacille Calmette-Guérin (BCG) vaccination, known to induce partial protection against TB, was used as a model system to investigate mechanistic relationships among different parameters of antigen-specific immunity. Effects of primary and booster intradermal BCG vaccinations were assessed in 3 distinct assays of mycobacterial inhibition. Correlations between vaccine-induced growth inhibition and other immune responses were analyzed. BCG significantly enhanced all antigen-specific responses. Peak responses occurred at 2 months after boosting. Statistical analyses suggested that each assay measured unique aspects of mycobacterial immunity. Despite previous evidence that type 1 immune responses are essential for TB immunity, interferon-gamma production did not correlate with mycobacterial inhibition. These results have important implications for TB vaccine development.

Failure to Control Growth of Mycobacteria in Blood from Children Infected with Human Immunodeficiency Virus and Its Relationship to T Cell Function

The Journal of Infectious Diseases. May, 2003  |  Pubmed ID: 12721934

The mechanisms of protective immunity to tuberculosis remain poorly understood in humans. A whole-blood infection model that employs a luminescent readout was used to analyze the role of T cells in control of mycobacterial infection. Control of mycobacterial growth in blood from healthy tuberculin-positive individuals was shown to be mediated predominantly by CD4(+) T cells. Comparison of age-matched cohorts of human immunodeficiency virus (HIV)-infected and -uninfected children from South Africa demonstrated an association between low CD4 cell counts, low interferon (IFN)-gamma production, and impaired ability to regulate growth of Mycobacterium bovis bacille Calmette-Guérin in blood from HIV-infected children. Impaired control of infection was not reconstituted by the addition of exogenous IFN-gamma. The whole-blood assay provides an important tool for monitoring and dissecting of human immune responses to mycobacterial infection.

Novel Human in Vitro System for Evaluating Antimycobacterial Vaccines

Infection and Immunity. Nov, 2004  |  Pubmed ID: 15501770

Major research efforts are directed towards the development of a better antimycobacterial vaccine. But progress in the field of tuberculosis vaccine development has been hampered by the lack of human in vitro models to assess vaccine immunogenicity and efficacy. New candidate vaccines will have to be evaluated against the existing Mycobacterium bovis BCG "gold standard." It is therefore important to understand the type of immune responses elicited by BCG vaccination to enable comparisons with potential new candidates. We used a novel human in vitro whole-blood model, which measures immune responses to mycobacteria by use of reporter gene-tagged BCG (BCG lux), to study immune responses to BCG vaccination in 50 neonates in a setting in Cape Town, Republic of South Africa, where tuberculosis is endemic. BCG vaccination significantly reduced growth of BCG lux in whole blood (prevaccination median growth ratio [GR], 9.6; range, 1.3 to 24; postvaccination median GR, 3.9; range, 0.6 to 12.2 [P < 0.0001]). Growth of BCG lux was better restricted in vaccinated infants than in unvaccinated age-matched controls (n = 4). BCG vaccination induced significantly higher gamma interferon production in response to BCG lux (P < 0.0001) and to purified protein derivative (P = 0.0001). No significant changes in either growth of BCG lux or cytokine production occurred in an adult control group (n = 6) over the study period. The whole-blood luminescence model detects changes in cellular immune responses to mycobacteria induced by BCG vaccination. It is therefore a useful new tool in studying the immunogenicity of newly developed vaccine candidates prior to large field trials assessing efficacy.

Acquired Predisposition to Mycobacterial Disease Due to Autoantibodies to IFN-gamma

The Journal of Clinical Investigation. Sep, 2005  |  Pubmed ID: 16127458

Genetic defects in the IFN-gamma response pathway cause unique susceptibility to intracellular pathogens, particularly mycobacteria, but are rare and do not explain mycobacterial disease in the majority of affected patients. We postulated that acquired defects in macrophage activation by IFN-gamma may cause a similar immunological phenotype and thus explain the occurrence of disseminated intracellular infections in some patients without identifiable immune deficiency. Macrophage activation in response to IFN-gamma and IFN-gamma production were studied in whole blood and PBMCs of 3 patients with severe, unexplained nontuberculous mycobacterial infection. In all 3 patients, IFN-gamma was undetectable following mitogen stimulation of whole blood, but significant quantities were detectable in the supernatants of PBMCs when stimulated in the absence of the patients' own plasma. The patients' plasma inhibited the ability of IFN-gamma to increase production of TNF-alpha by both autologous and normal donor PBMCs, and recovery of exogenous IFN-gamma from the patients' plasma was greatly reduced. Using affinity chromatography, surface-enhanced laser desorption/ionization mass spectrometry, and sequencing, we isolated an IFN-gamma-neutralizing factor from the patients' plasma and showed it to be an autoantibody against IFN-gamma. The purified anti-IFN-gamma antibody was shown to be functional first in blocking the upregulation of TNF-alpha production in response to endotoxin; second in blocking induction of IFN-gamma-inducible genes (according to results of high-density cDNA microarrays); and third in inhibiting upregulation of HLA class II expression on PBMCs. Acquired defects in the IFN-gamma pathway may explain unusual susceptibility to intracellular pathogens in other patients without underlying, genetically determined immunological defects.

Reconstitution of Antimycobacterial Immune Responses in HIV-infected Children Receiving HAART

AIDS (London, England). Apr, 2006  |  Pubmed ID: 16603853

Recent epidemiological studies in adults suggest that HAART can prevent the development of tuberculosis in HIV-infected individuals, but the mechanisms are incompletely understood and no data exist in children. We investigated whether changes in mycobacterial-specific immune responses can be demonstrated in children after commencing antiretroviral therapy.

Blood Tests for Diagnosis of Tuberculosis

Lancet. Jul, 2006  |  Pubmed ID: 16860689

A Deletion Defining a Common Asian Lineage of Mycobacterium Tuberculosis Associates with Immune Subversion

Proceedings of the National Academy of Sciences of the United States of America. Oct, 2006  |  Pubmed ID: 17028173

Six major lineages of Mycobacterium tuberculosis appear preferentially transmitted amongst distinct ethnic groups. We identified a deletion affecting Rv1519 in CH, a strain isolated from a large outbreak in Leicester U.K., that coincidentally defines the East African-Indian lineage matching a major ethnic group in this city. In broth media, CH grew less rapidly and was less acidic and H2O2-tolerant than reference sequenced strains (CDC1551 and H37Rv). Nevertheless, CH was not impaired in its ability to grow in human monocyte-derived macrophages. When compared with CDC1551 and H37Rv, CH induced less protective IL-12p40 and more antiinflammatory IL-10 and IL-6 gene transcription and secretion from monocyte-derived macrophages. It thus appears that CH compensates microbiological attenuation by skewing the innate response toward phagocyte deactivation. Complementation of Rv1519, but none of nine additional genes absent from CH compared with the type strain, H37Rv, reversed the capacity of CH to elicit antiinflammatory IL-10 production by macrophages. The Rv1519 polymorphism in M. tuberculosis confers an immune subverting phenotype that contributes to the persistence and outbreak potential of this lineage.

Dendritic Cell Stimulation by Mycobacterial Hsp70 is Mediated Through CCR5

Science (New York, N.Y.). Oct, 2006  |  Pubmed ID: 17053144

An effective host immune response to mycobacterial infection must control pathogen dissemination without inducing immunopathology. Constitutive overexpression of mycobacterial heat shock protein (myHsp70) is associated with impaired bacterial persistence, but the immune-mediated mechanisms are unknown. We found that myHsp70, in addition to enhancing antigen delivery to human dendritic cells, signaled through the CCR5 chemokine receptor, promoting dendritic cell aggregation, immune synapse formation between dendritic cells and T cells, and the generation of effector immune responses. Thus, CCR5 acts as a pattern-recognition receptor for myHsp70, which may have implications for both the pathophysiology of tuberculosis and the use of myHsps in tumor-directed immunotherapy.

Enhanced Anti-mycobacterial Immunity in Children with Erythema Nodosum and a Positive Tuberculin Skin Test

The Journal of Investigative Dermatology. Sep, 2007  |  Pubmed ID: 17460727

Erythema nodosum (EN) may follow a variety of infections, but in regions with a high prevalence of tuberculosis, is frequently associated with a positive tuberculin skin test (TST) and tuberculosis infection. We aimed to investigate the immunological differences between patients with EN as a manifestation of primary tuberculosis, and those with progressive pulmonary tuberculosis (PTB) or asymptomatic infection. We studied the inflammatory response to both mycobacterial and non-mycobacterial antigens in 11 children with EN associated with a positive TST, 22 children with culture-confirmed tuberculosis, and 53 healthy skin test-positive children. In addition, we evaluated functional anti-mycobacterial immunity using an ex vivo assay of mycobacterial growth restriction in five children with EN and 15 with PTB. Patients with EN were distinguished by enhanced mycobacterial growth restriction on the functional assay, which was associated with a markedly increased production of IFNgamma in response to stimulation with purified protein derivative of Mycobacterium tuberculosis. Children presenting with EN and a positive TST show evidence of responses associated with enhanced anti-mycobacterial immunity.

A Single Dose of Vitamin D Enhances Immunity to Mycobacteria

American Journal of Respiratory and Critical Care Medicine. Jul, 2007  |  Pubmed ID: 17463418

Vitamin D was used to treat tuberculosis (TB) in the preantibiotic era. Prospective studies to evaluate the effect of vitamin D supplementation on antimycobacterial immunity have not previously been performed.

IFN-gamma- and TNF-independent Vitamin D-inducible Human Suppression of Mycobacteria: the Role of Cathelicidin LL-37

Journal of Immunology (Baltimore, Md. : 1950). Jun, 2007  |  Pubmed ID: 17513768

Vitamin D deficiency is associated with susceptibility to tuberculosis, and its biologically active metabolite, 1alpha,25 dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)), has pleiotropic immune effects. The mechanisms by which 1alpha,25(OH)(2)D(3) protects against tuberculosis are incompletely understood. 1alpha,25(OH)(2)D(3) reduced the growth of mycobacteria in infected human PBMC cultures in a dose-dependent fashion. Coculture with agonists or antagonists of the membrane or nuclear vitamin D receptors indicated that these effects were primarily mediated by the nuclear vitamin D receptors. 1alpha,25(OH)(2)D(3) reduced transcription and secretion of protective IFN-gamma, IL-12p40, and TNF in infected PBMC and macrophages, indicating that 1alpha,25(OH)(2)D(3) does not mediate protection via these cytokines. Although NOS2A was up-regulated by 1alpha,25(OH)(2)D(3), inhibition of NO formation marginally affected the suppressive effect of 1alpha,25(OH)(2)D(3) on bacillus Calmette Guérin in infected cells. By contrast, 1alpha,25(OH)(2)D(3) strongly up-regulated the cathelicidin hCAP-18 gene, and some hCAP-18 polypeptide colocalized with CD14 in 1alpha,25(OH)(2)D(3) stimulated PBMC, although no detectable LL-37 peptide was found in supernatants from similar 1alpha,25(OH)(2)D(3)-stimulated PBMC cultures. A total of 200 mug/ml of the active peptide LL-37, in turn, reduced the growth of Mycobacterium tuberculosis in culture by 75.7%. These findings suggest that vitamin D contributes to protection against TB by "nonclassical" mechanisms that include the induction of antimicrobial peptides.

Neutrophil-mediated Innate Immune Resistance to Mycobacteria

The Journal of Clinical Investigation. Jul, 2007  |  Pubmed ID: 17607367

Neutrophils contain antimicrobial peptides with antituberculous activity, but their contribution to immune resistance to tuberculosis (TB) infection has not been previously investigated to our knowledge. We determined differential white cell counts in peripheral blood of 189 adults who had come into contact with patients diagnosed with active TB in London, United Kingdom, and evaluated them for evidence of TB infection and capacity to restrict mycobacterial growth in whole-blood assays. Risk of TB infection was inversely and independently associated with peripheral blood neutrophil count in contacts of patients diagnosed with pulmonary TB. The ability of whole blood to restrict growth of Mycobacterium bovis bacille Calmette Guérin and Mycobacterium tuberculosis was impaired 7.3- and 3.1-fold, respectively, by neutrophil depletion. In microbiological media, human neutrophil peptides (HNPs) 1-3 killed M. tuberculosis. The neutrophil peptides cathelicidin LL-37 and lipocalin 2 restricted growth of the organism, the latter in an iron-dependent manner. Black African participants had lower neutrophil counts and lower circulating concentrations of HNP1-3 and lipocalin 2 than south Asian and white participants. Neutrophils contribute substantially to innate resistance to TB infection, an activity associated with their antimicrobial peptides. Elucidation of the regulation of neutrophil antimicrobial peptides could facilitate prevention and treatment of TB.

Small Molecule Enhancers of Rapamycin-induced TOR Inhibition Promote Autophagy, Reduce Toxicity in Huntington's Disease Models and Enhance Killing of Mycobacteria by Macrophages

Autophagy. Nov-Dec, 2007  |  Pubmed ID: 17786022

Upregulation of autophagy may have therapeutic benefit in a range of diseases that includes neurodegenerative conditions caused by intracytosolic aggregate-prone proteins, such as Huntington's disease, and certain infectious diseases, such as tuberculosis. The best-characterized drug that enhances autophagy is rapamycin, an inhibitor of the TOR (target of rapamycin) proteins, which are widely conserved from yeast to man. Unfortunately, the side effects of rapamycin, especially immunosuppression, preclude its use in treating certain diseases including tuberculosis, which accounts for approximately 2 million deaths worldwide each year, spurring interest in finding novel drugs that selectively enhance autophagy. We have recently reported a novel two-step screening process for the discovery of such compounds. We first identified compounds that enhance the growth-inhibitory effects of rapamycin in the budding yeast Saccharomyces cerevisiae, which we termed small molecule enhancers of rapamycin (SMERs). Next we showed that three SMERs induced autophagy independently, or downstream of mTOR, in mammalian cells, and furthermore enhanced the clearance of a mutant huntingtin fragment in Huntington's disease cell models. These SMERs also protected against mutant huntingtin fragment toxicity in Drosophila. We have subsequently tested two of the SMERs in models of tuberculosis and both enhance the killing of mycobacteria by primary human macrophages.

Childhood Tuberculosis: out of Sight, out of Mind?

Transactions of the Royal Society of Tropical Medicine and Hygiene. Mar, 2008  |  Pubmed ID: 17996915

Despite significant improvements in tuberculosis (TB) management under the WHO directly observed treatment, short course (DOTS) strategy, childhood TB has been relatively neglected. Children are at high risk of severe disease, and reactivation of latent infection in adulthood perpetuates the epidemic. Almost a million cases of childhood TB are estimated to occur annually, but good-quality epidemiological data are scarce due to inherent difficulties diagnosing paediatric TB. There remains an urgent need both for better diagnostic tests and for robust regional data on the true burden of disease, otherwise childhood TB will remain an essentially 'invisible' and therefore neglected disease.

Reduction of Chemokine Secretion in Response to Mycobacteria in Infliximab-treated Patients

Clinical and Vaccine Immunology : CVI. Mar, 2008  |  Pubmed ID: 18160618

The use of anti-tumor necrosis factor (TNF) agents as a treatment for chronic inflammatory conditions has been shown to be associated with an increased risk of developing tuberculosis. We studied the effect of the anti-TNF antibody infliximab on antimycobacterial immunity in 26 patients with rheumatoid arthritis or ankylosing spondylitis by use of an in vitro whole-blood model employing a reporter mycobacterium. Blood samples taken before and 30 min and 7 days after a 2-hour infliximab infusion were compared in terms of their abilities both to suppress luminescence of Mycobacterium bovis bacillus Calmette-Guérin lux and to secrete chemokines and cytokines 24 and 96 h after infection. No immediate effect of infliximab on mycobacterial luminescence was detected using this bioassay, irrespective of whether patients were receiving their first (n = 14) or maintenance (n = 12) doses of infliximab. Moreover, no effect on mycobacterial luminescence was detected when blood was taken 7 days after infliximab treatment (n = 7). By contrast, there was a significant reduction in the chemokines implicated in cellular trafficking, namely, interleukin-8, macrophage-inhibitory protein-1alpha (MIP-1alpha), MIP-1beta (24 h and 96 h), and monocyte chemoattractant protein-1 (MCP-1) (24 h) following BCG lux strain infection in the 30-minute post-infliximab-infusion blood samples (P < 0.05). This effect was sustained by MIP-1beta and MCP-1 (24 h; P < 0.05) at 7 days after infusion. Our results suggest that the development of tuberculosis in infliximab-treated patients is not directly related to the mycobactericidal effects of TNF but may be due to inhibition of TNF-dependent chemokine gradients disrupting cellular migration necessary to maintain the integrity of the granuloma.

Paediatric Tuberculosis

The Lancet Infectious Diseases. Aug, 2008  |  Pubmed ID: 18652996

Tuberculosis continues to cause an unacceptably high toll of disease and death among children worldwide, particularly in the wake of the HIV epidemic. Increased international travel and immigration have led to a rise in childhood tuberculosis rates even in traditionally low burden, industrialised settings, and threaten to promote the emergence and spread of multidrug-resistant strains. Whereas intense scientific and clinical research efforts into novel diagnostic, therapeutic, and preventive interventions have focused on tuberculosis in adults, childhood tuberculosis has been relatively neglected. However, children are particularly vulnerable to severe disease and death following infection, and those with latent infection become the reservoir for future transmission following disease reactivation in adulthood, fuelling future epidemics. Further research into the epidemiology, immune mechanisms, diagnosis, treatment, and prevention of childhood tuberculosis is urgently needed. Advances in our understanding of tuberculosis in children would provide insights and opportunities to enhance efforts to control this disease.

Perinatal Tuberculosis: New Challenges in the Diagnosis and Treatment of Tuberculosis in Infants and the Newborn

Early Human Development. Dec, 2008  |  Pubmed ID: 18823726

With increasing rates of tuberculosis (TB) infection and disease worldwide, the rate of perinatal TB is also affected. A high index of suspicion by health professionals, in both the developed and developing world, is required to detect and manage tuberculosis in pregnancy and the early newborn period. Differences in immune responses in the fetus and neonate add to the diagnostic difficulties already recognised in young children. Although specific guidelines for the treatment of this potentially devastating disease are lacking due to paucity of experience, outcome is favourable, if the condition is recognised and treated according to existing TB protocols. HIV co-infection, multi- and extensively-drug resistant (MDR/XDR) TB contribute to the challenges. New diagnostic and vaccine developments hold future promise, but much work is needed to completely understand the complex immune responses to tuberculosis and control this disease.

Is IP-10 a Better Biomarker for Active and Latent Tuberculosis in Children Than IFNgamma?

PloS One. 2008  |  Pubmed ID: 19065267

The blood based interferon-gamma release assays (IGRA) for the diagnosis of tuberculosis do not discriminate between active TB disease and latent TB infection (LTBI). The search for distinguishing biomarkers therefore continues, as the accurate diagnosis of tuberculosis is particularly challenging in children. IFN-gamma-inducible protein 10 (IP-10/CXCL10) has recently been evaluated as a marker for active TB in adults with promising results.

Comparison of Interferon-gamma Release Assays and Tuberculin Skin Test in Predicting Active Tuberculosis (TB) in Children in the UK: a Paediatric TB Network Study

Archives of Disease in Childhood. Mar, 2010  |  Pubmed ID: 19815937

The value of interferon-gamma release assays (IGRA) to diagnose active tuberculosis (TB) in children is not established, but these assays are being widely used for this purpose. The authors examined the sensitivity of commercially available IGRA to diagnose active TB in children in the UK compared with the tuberculin skin test (TST).

CD4 and CD8 T-cell Responses to Mycobacterial Antigens in African Children

American Journal of Respiratory and Critical Care Medicine. Jul, 2010  |  Pubmed ID: 20224065

The current tuberculosis (TB) vaccine, bacille Calmette-Guérin (BCG), does not provide adequate protection against TB disease in children. Furthermore, more efficacious TB vaccines are needed for children with immunodeficiencies such as HIV infection, who are at highest risk of disease.

Impact of Immigration on Pulmonary Tuberculosis in Spanish Children

The Pediatric Infectious Disease Journal. Jul, 2010  |  Pubmed ID: 20300046

Immunology and Pathogenesis of Childhood TB

Paediatric Respiratory Reviews. Mar, 2011  |  Pubmed ID: 21172668

Maternal HIV Infection and Antibody Responses Against Vaccine-preventable Diseases in Uninfected Infants

JAMA : the Journal of the American Medical Association. Feb, 2011  |  Pubmed ID: 21304083

Altered immune responses might contribute to the high morbidity and mortality observed in human immunodeficiency virus (HIV)-exposed uninfected infants.

Kawasaki Disease Coincident with Influenza A H1N1/09 Infection

Pediatrics International : Official Journal of the Japan Pediatric Society. Feb, 2011  |  Pubmed ID: 21342333

Age-dependent Maturation of Toll-like Receptor-mediated Cytokine Responses in Gambian Infants

PloS One. 2011  |  Pubmed ID: 21533209

The global burden of neonatal and infant mortality due to infection is staggering, particularly in resource-poor settings. Early childhood vaccination is one of the major interventions that can reduce this burden, but there are specific limitations to inducing effective immunity in early life, including impaired neonatal leukocyte production of Th1-polarizing cytokines to many stimuli. Characterizing the ontogeny of Toll-like receptor (TLR)-mediated innate immune responses in infants may shed light on susceptibility to infection in this vulnerable age group, and provide insights into TLR agonists as candidate adjuvants for improved neonatal vaccines. As little is known about the leukocyte responses of infants in resource-poor settings, we characterized production of Th1-, Th2-, and anti-inflammatory-cytokines in response to agonists of TLRs 1-9 in whole blood from 120 Gambian infants ranging from newborns (cord blood) to 12 months of age. Most of the TLR agonists induced TNFα, IL-1β, IL-6, and IL-10 in cord blood. The greatest TNFα responses were observed for TLR4, -5, and -8 agonists, the highest being the thiazoloquinoline CLO75 (TLR7/8) that also uniquely induced cord blood IFNγ production. For most agonists, TLR-mediated TNFα and IFNγ responses increased from birth to 1 month of age. TLR8 agonists also induced the greatest production of the Th1-polarizing cytokines TNFα and IFNγ throughout the first year of life, although the relative responses to the single TLR8 agonist and the combined TLR7/8 agonist changed with age. In contrast, IL-1β, IL-6, and IL-10 responses to most agonists were robust at birth and remained stable through 12 months of age. These observations provide fresh insights into the ontogeny of innate immunity in African children, and may inform development of age-specific adjuvanted vaccine formulations important for global health.

Early Deaths During Tuberculosis Treatment Are Associated with Depressed Innate Responses, Bacterial Infection, and Tuberculosis Progression

The Journal of Infectious Diseases. Aug, 2011  |  Pubmed ID: 21742833

Up to 14% of Malawian adults die during the intensive phase of tuberculosis treatment. In a prospective cohort of 199 Malawian adults with microbiologically confirmed pulmonary tuberculosis, clinical and laboratory parameters were compared between those who died or deteriorated with those who had an uneventful recovery. Baseline tumor necrosis factor alpha responses to stimulation with heat-killed Mycobacterium tuberculosis and lipopolysaccharide were reduced among the 22 patients with poor outcome (P = .017). Low body mass index (P = .002) and elevated respiratory rate (P = .01) at tuberculosis diagnosis independently predicted poor outcome. Validation of a clinical score identifying high-risk individuals is warranted, together with further investigation of immunological derangements.

Azithromycin Blocks Autophagy and May Predispose Cystic Fibrosis Patients to Mycobacterial Infection

The Journal of Clinical Investigation. Sep, 2011  |  Pubmed ID: 21804191

Azithromycin is a potent macrolide antibiotic with poorly understood antiinflammatory properties. Long-term use of azithromycin in patients with chronic inflammatory lung diseases, such as cystic fibrosis (CF), results in improved outcomes. Paradoxically, a recent study reported that azithromycin use in patients with CF is associated with increased infection with nontuberculous mycobacteria (NTM). Here, we confirm that long-term azithromycin use by adults with CF is associated with the development of infection with NTM, particularly the multi-drug-resistant species Mycobacterium abscessus, and identify an underlying mechanism. We found that in primary human macrophages, concentrations of azithromycin achieved during therapeutic dosing blocked autophagosome clearance by preventing lysosomal acidification, thereby impairing autophagic and phagosomal degradation. As a consequence, azithromycin treatment inhibited intracellular killing of mycobacteria within macrophages and resulted in chronic infection with NTM in mice. Our findings emphasize the essential role for autophagy in the host response to infection with NTM, reveal why chronic use of azithromycin may predispose to mycobacterial disease, and highlight the dangers of inadvertent pharmacological blockade of autophagy in patients at risk of infection with drug-resistant pathogens.