The inducing role of tumor necrosis factor in the development of bactericidal granulomas during BCG infection

Granuloma formation in the liver of mice infected with BCG coincides with local TNF synthesis. Injection of rabbit anti-TNF antibody, after 1 or 2 weeks of infection, dramatically interferes with the development of granulomas (both in number and size, large epithelioid cells failing to appear) and subsequent mycobacterial elimination. Furthermore, fully developed BCG granulomas, after 3 weeks of infection, rapidly regress after anti-TNF treatment. Antibody treatment also prevents or suppresses accumulation of TNF mRNA and protein, which resumes after disappearance of the antibody. Peritoneal macrophages exposed to TNF transiently accumulate TNF mRNA, and show an enhanced increase in TNF mRNA in response to gamma interferon. We propose that TNF released from macrophages in the microenvironment of developing granulomas is involved in a process of autoamplification: acting in an autocrine or paracrine way, it enhances its own synthesis and release, thus favoring further macrophage accumulation and differentiation leading to bacterial elimination.

Tuberculosis and diabetes mellitus: convergence of two epidemics

The link between diabetes mellitus and tuberculosis has been recognised for centuries. In recent decades, tuberculosis incidence has declined in high-income countries, but incidence remains high in countries that have high rates of infection with HIV, high prevalence of malnutrition and crowded living conditions, or poor tuberculosis control infrastructure. At the same time, diabetes mellitus prevalence is soaring globally, fuelled by obesity. There is growing evidence that diabetes mellitus is an important risk factor for tuberculosis and might affect disease presentation and treatment response. Furthermore, tuberculosis might induce glucose intolerance and worsen glycaemic control in people with diabetes. We review the epidemiology of the tuberculosis and diabetes epidemics, and provide a synopsis of the evidence for the role of diabetes mellitus in susceptibility to, clinical presentation of, and response to treatment for tuberculosis. In addition, we review potential mechanisms by which diabetes mellitus can cause tuberculosis, the effects of tuberculosis on diabetic control, and pharmacokinetic issues related to the co-management of diabetes and tuberculosis.

Drug tolerance in replicating mycobacteria mediated by a macrophage-induced efflux mechanism

Treatment of tuberculosis, a complex granulomatous disease, requires long-term multidrug therapy to overcome tolerance, an epigenetic drug resistance that is widely attributed to nonreplicating bacterial subpopulations. Here, we deploy Mycobacterium marinum-infected zebrafish larvae for in vivo characterization of antitubercular drug activity and tolerance. We describe the existence of multidrug-tolerant organisms that arise within days of infection, are enriched in the replicating intracellular population, and are amplified and disseminated by the tuberculous granuloma. Bacterial efflux pumps that are required for intracellular growth mediate this macrophage-induced tolerance. This tolerant population also develops when Mycobacterium tuberculosis infects cultured macrophages, suggesting that it contributes to the burden of drug tolerance in human tuberculosis. Efflux pump inhibitors like verapamil reduce this tolerance. Thus, the addition of this currently approved drug or more specific efflux pump inhibitors to standard antitubercular therapy should shorten the duration of curative treatment.

Paediatric tuberculosis

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.

Dormancy of Mycobacterium tuberculosis and latency of disease

There is ample circumstantial evidence from observation of the natural history of tuberculosis in humans and experimental animals that Mycobacterium tuberculosis is capable of adapting to prolonged periods of dormancy in tissues, and that these dormant bacilli are responsible for latency of the disease itself. Furthermore, the dormant bacilli are resistant to killing by antimycobacterial agents. A systematic evaluation of the mechanism of dormancy, and of attempts to abrogate latency will require a better understanding of the physiologic events that attend the shiftdown into dormancy. There are probably two or more stages in the shiftdown of Mycobacterium tuberculosis from active replication to dormancy as bacilli in unagitated cultures settle through a self-generated O2 gradient into a sediment where O2 is severely limited. One step involves a shift from rapid to slow replication. The other involves complete shutdown of replication, but not death. Presumably this last step includes completion of a round of DNA synthesis. The shiftup on resumption of aeration includes at least three discrete sequential steps, the production of RNA, the ensuing synchronized cell division and, finally, the initiation of a new round of synthesis of DNA. Three markers of the process of shiftdown of Mycobacterium tuberculosis to dormancy have been described, namely the changes in tolerance to anaerobiosis, the production of a unique antigen and the ten-fold increase in glycine dehydrogenase production. Additional markers represented in the shiftup and shiftdown process may yet be discovered, and determination of their specific functions should provide insights into the mechanisms of dormancy and latency in tuberculosis, and into strategies for preventing reactivation of the bacilli and development of disease.

Revisiting the timetable of tuberculosis

Tuberculosis has a much shorter incubation period than is widely thought, say Marcel A Behr and colleagues, and this has implications for prioritising research and public health strategies

IL-17 and Th17 cells in tuberculosis

Tuberculosis is primarily a disease of the lung. Constant expression of cellular immunity in this organ is required to control Mycobacterium tuberculosis growth, but this can also result in chronic inflammation and pathologic consequences. During primary tuberculosis both IFN-γ and IL-17 are induced: both are potent inflammatory cytokines capable of inducing expression of chemokines that promote cell recruitment and granuloma organization throughout infection. During the chronic phase, a balance between Th1 and Th17 responses needs to be achieved to control bacterial growth and limit immunopathology, as a shift of the response towards excessive IL-17 production may sustain extensive neutrophil recruitment and tissue damage. Thus, regulation of Th1 and Th17 responses during tuberculosis is essential to promote anti-mycobacterial immunity and prevent extensive immunopathological consequences.

A replication clock for Mycobacterium tuberculosis

Few tools exist to assess replication of chronic pathogens during infection. This has been a considerable barrier to understanding latent tuberculosis, and efforts to develop new therapies generally assume that the bacteria are very slowly replicating or nonreplicating during latency. To monitor Mycobacterium tuberculosis replication within hosts, we exploit an unstable plasmid that is lost at a steady, quantifiable rate from dividing cells in the absence of antibiotic selection. By applying a mathematical model, we calculate bacterial growth and death rates during infection of mice. We show that during chronic infection, the cumulative bacterial burden-enumerating total live, dead and removed organisms encountered by the mouse lung-is substantially higher than estimates from colony-forming units. Our data show that M. tuberculosis replicates throughout the course of chronic infection of mice and is restrained by the host immune system. This approach may also shed light on the replication dynamics of other chronic pathogens.

Oxygenated mycolic acids are necessary for virulence of Mycobacterium tuberculosis in mice

Members of the Mycobacterium tuberculosis group synthesize a family of long-chain fatty acids, mycolic acids, which are located in the cell envelope. These include the non-oxygenated alpha-mycolic acid and the oxygenated keto- and methoxymycolic acids. The function in bacterial virulence, if any, of these various types of mycolic acids is unknown. We have constructed a mutant strain of M. tuberculosis with an inactivated hma (cmaA, mma4) gene; this mutant strain no longer synthesizes oxygenated mycolic acids, has profound alterations in its envelope permeability and is attenuated in mice.

Identification of Risk Factors for Extrapulmonary Tuberculosis

The proportion of extrapulmonary tuberculosis cases in the United States has increased from 16% of tuberculosis cases, in 1991, to 20%, in 2001. To determine associations between the demographic, clinical, and life style characteristics of patients with tuberculosis and the occurrence of extrapulmonary tuberculosis, a retrospective case-control study was conducted. This study included 705 patients with tuberculosis, representing 98% of the culture-proven cases of tuberculosis in Arkansas from 1 January 1996 through 31 December 2000. A comparison between 85 patients with extrapulmonary tuberculosis (case patients) and 620 patients with pulmonary tuberculosis (control patients) showed women (OR, 1.98; 95% CI, 1.25-3.13), non-Hispanic blacks (OR, 2.38; 95% CI, 1.42-3.97), and HIV-positive persons (OR, 4.93; 95% CI, 1.95-12.46) to have a significantly higher risk for extrapulmonary tuberculosis than men, non-Hispanic whites, and HIV-negative persons. This study expands the knowledge base regarding the epidemiology of extrapulmonary tuberculosis and enhances our understanding of the relative contribution of host-related factors to the pathogenesis of tuberculosis.

Mycobacterium tuberculosis Infection in Recipients of Solid Organ Transplants

Tuberculosis is a serious opportunistic infection that may affect transplant recipients. The incidence of tuberculosis among such persons is 20-74 times higher than that for the general population, with a mortality rate of up to 30%. The most common form of acquisition of tuberculosis after transplantation is the reactivation of latent tuberculosis in patients with previous exposure. Clinical presentation is frequently atypical and diverse, with unsuspected and elusive sites of affection. Manifestations include fever of unknown origin and allograft dysfunction. Coinfection with other pathogens is not uncommon. New techniques, such as PCR and quantification of interferon- gamma , have been developed to achieve more-rapid and -accurate diagnoses. Treatment requires control of interactions between antituberculous drugs and immunosuppressive therapy. Prophylaxis against latent tuberculosis is the main approach to treatment, but many issues remain unsolved, because of the difficulty in identifying patients at risk (such as those with nonreactive purified protein derivative test results) and the toxicity of therapy.

Mycobacterium tuberculosis and the intimate discourse of a chronic infection

Mycobacterium tuberculosis is an extremely successful pathogen that demonstrates the capacity to modulate its host both at the cellular and tissue levels. At the cellular level, the bacterium enters its host macrophage and arrests phagosome maturation, thus avoiding many of the microbicidal responses associated with this phagocyte. Nonetheless, the intracellular environment places certain demands on the pathogen, which, in response, senses the environmental shifts and upregulates specific metabolic programs to allow access to nutrients, minimize the consequences of stress, and sustain infection. Despite its intracellular niche, Mycobacterium tuberculosis demonstrates a marked capacity to modulate the tissues surrounding infected cells through the release of potent, bioactive cell wall constituents. These cell wall lipids are released from the host cell by an exocytic process and induce physiological changes in neighboring phagocytes, which drives formation of a granuloma. This tissue response leads to the generation and accumulation of caseous debris and the progression of the human tuberculosis granuloma. Completion of the life cycle of tuberculosis requires damaging the host to release infectious bacteria into the airways to spread the infection. This damage reflects the pathogen's ability to subvert the host's innate and acquired immune responses to its own nefarious ends.

Innate immunity in tuberculosis: myths and truth

Tuberculosis is the most important bacterial infection world wide. The causative agent, Mycobacterium tuberculosis survives and proliferates within macrophages. Immune mediators such as interferon gamma (IFN-gamma) and tumour necrosis factor alpha (TNF-alpha) activate macrophages and promote bacterial killing. IFN-gamma is predominantly secreted by innate cells (mainly natural killer (NK) cells) and by T cells upon instruction by interleukin 12 (IL-12) and IL-18. These cytokines are primarily produced by dendritic cells and macrophages in response to Toll-like receptor (TLR) signalling interaction with tubercle bacilli. These signals also induce pro-inflammatory cytokines (including IL-1beta and TNF-alpha), chemokines and defensins. The inflammatory environment further recruits innate effector cells such as macrophages, polymorphonuclear neutrophils (PMN) and NK cells to the infectious foci. This eventually leads to the downstream establishment of acquired T cell immunity which appears to be protective in more than 90% of infected individuals. Robust innate immune activation is considered an essential prerequisite for protective immunity and vaccine efficacy. However, data published so far provide a muddled view of the functional importance of innate immunity in tuberculosis. Here we critically discuss certain aspects of innate immunity, namely PMN, TLRs and NK cells, as characterised in tuberculosis to date, and their contribution to protection and pathology.

The Mycobacterium tuberculosis FAS-II condensing enzymes: their role in mycolic acid biosynthesis, acid-fastness, pathogenesis and in future drug development

Mycolic acids are very long-chain fatty acids representing essential components of the mycobacterial cell wall. Considering their importance, characterization of key enzymes participating in mycolic acid biosynthesis not only allows an understanding of their role in the physiology of mycobacteria, but also might lead to the identification of new drug targets. Mycolates are synthesized by at least two discrete elongation systems, the type I and type II fatty acid synthases (FAS-I and FAS-II respectively). Among the FAS-II components, the condensing enzymes that catalyse the formation of carbon-carbon bonds have received considerable interest. Four condensases participate in initiation (mtFabH), elongation (KasA and KasB) and termination (Pks13) steps, leading to full-length mycolates. We present the recent biochemical and structural data for these important enzymes. Special emphasis is given to their role in growth, intracellular survival, biofilm formation, as well as in the physiopathology of tuberculosis. Recent studies demonstrated that phosphorylation of these enzymes by mycobacterial kinases affects their activities. We propose here a model in which kinases that sense environmental changes can phosphorylate the condensing enzymes, thus representing a novel mechanism of regulating mycolic acid biosynthesis. Finally, we discuss the attractiveness of these enzymes as valid targets for future antituberculosis drug development.

Execution of macrophage apoptosis by PE_PGRS33 of Mycobacterium tuberculosis is mediated by Toll-like receptor 2-dependent release of tumor necrosis factor-alpha

Combating tuberculosis requires a detailed understanding of how mycobacterial effectors modulate the host immune response. The role of the multigene PE family of proteins unique to mycobacteria in the pathogenesis of tuberculosis is still poorly understood, although certain PE_PGRS genes have been linked to virulence. Tumor necrosis factor-alpha (TNF-alpha) is essential for successfully combating tuberculosis. In this study we provide evidence that PE_PGRS33, a surface exposed protein, elicits TNF-alpha release from macrophages in a TLR2 (Toll-like receptor 2)-dependent manner. ASK1 (apoptosis signal-regulating kinase 1) is activated downstream of TLR2. ASK1 activates the MAPKs p38 and JNK. PE_PGRS33-induced signaling leads to enhanced expression of TNF-alpha and TNF receptor I (TNFRI) genes. Mycobacterium smegmatis expressing PE_ PGRS33 elicits the same effects as purified PE_PGRS33. TNF-alpha release occurs even when internalization of the bacteria is blocked by cytochalasin D, suggesting that interaction of PE_ PGRS33 with TLR2 is sufficient to trigger the effects described. Release of TNF-alpha plays the determining role in triggering apoptosis in macrophages challenged with PE_PGRS33. The death receptor-dependent signals are amplified through classical caspase 8-dependent mitochondrial release of cytochrome c, leading to the activation of caspases 9 and 3. An important aspect of our findings is that deletions within the PGRS domain (simulating those occurring in clinical strains) attenuate the TNF-alpha-inducing ability of PE_PGRS33. These results provide the first evidence that variations in the polymorphic repeats of the PGRS domain modulate the innate immune response.

Improving tuberculosis prevention and care through addressing the global diabetes epidemic: from evidence to policy and practice

Diabetes triples the risk of tuberculosis and is also a risk factor for adverse tuberculosis treatment outcomes, including death. Prevalence of diabetes is increasing globally, but most rapidly in low-income and middle-income countries where tuberculosis is a grave public health problem. Growth in this double disease burden creates additional obstacles for tuberculosis care and prevention. We review how the evolution of evidence on the link between tuberculosis and diabetes has informed global policy on collaborative activities, and how practice is starting to change as a consequence. We conclude that coordinated planning and service delivery across communicable and non-communicable disease programmes is necessary, feasible, and creates synergies that will help to reduce the burden of both tuberculosis and diabetes.

Histoplasmosis in the acquired immune deficiency syndrome

This report describes the experience with disseminated histoplasmosis in seven of 15 patients with the acquired immune deficiency syndrome (AIDS) diagnosed in Indianapolis since 1981. Three were homosexual, two were intravenous drug addicts, one was the spouse of another patient with AIDS and disseminated histoplasmosis, and the seventh was a hemophiliac. Six had associated infections: candidiasis in three, Pneumocystis carinii pneumonia, recurrent mucocutaneous herpes simplex infection, and disseminated Mycobacterium avium infection in two each, and disseminated infection with an unidentified mycobacterium in one. Clinical diseases suggested sepsis in four. Histoplasma fungemia occurred in five, but the diagnosis was established first by visualization of organisms in blood or bone marrow in three. Results of Histoplasma serologic tests were positive in each. Three died before receiving 50 mg of amphotericin B, three had prompt improvement with amphotericin B, and one was treated with ketoconazole to prevent dissemination. However, two of the three patients treated with amphotericin B had relapses after a 35 mg/kg course, and the third died within a month following therapy. Disseminated histoplasmosis is a major opportunistic infection in patients with AIDS from endemic areas. AIDS should be strongly considered in otherwise healthy persons with disseminated histoplasmosis, especially if risk factors for AIDS are present. Amphotericin B is not curative in these patients.

Chemokines induced by infection of mononuclear phagocytes with mycobacteria and present in lung alveoli during active pulmonary tuberculosis

The capacity of Mycobacterium tuberculosis (MTB) to induce production of chemokines with known chemotactic activity for monocytes and lymphocytes, the cellular building blocks of granulomas, was investigated. These chemokines included regulated upon activation, normal T cell expressed and secreted (RANTES), monocyte chemotactic protein-1 (MCP-1), and macrophage inflammatory protein-1alpha (MIP-1alpha). MTB stimulated production of MCP-1 and MIP-1alpha by blood monocytes (MN) and alveolar macrophages (AM). MTB infection of MN and AM stimulated release but not production of RANTES. AM produced or released significantly higher levels than MN of RANTES (by 2.1-fold), MCP-1 (by 6.9-fold), and MIP-1alpha (by 5. 5-fold) (P < 0.05 for each). This study also confirmed that MTB-infected AM produce the chemokine interleukin (IL)-8. MTB infection of AM resulted in increased steady-state expression of messenger RNA (mRNA) for MCP-1 and MIP-1alpha and minimal increased expression of RANTES mRNA. Both an avirulent (H37Ra) and a virulent (H37Rv) strain of MTB and purified protein derivative of H37Rv but not latex beads induced production of chemokines. Supernatants of MTB-infected cells demonstrated chemotactic activity for both monocytes and lymphocytes partially inhibitable by neutralizing antibodies against the chemokines studied. Bronchoalveolar lavage fluid from patients with active pulmonary tuberculosis as compared with healthy control subjects contained increased levels of RANTES (by 8-fold), MCP-1 (by 2.7-fold), and IL-8 (by 8.9-fold) (P < 0.05), but not MIP-1alpha, as compared with healthy control subjects. Thus, multiple chemokines may be involved in recruitment of cells for granuloma formation in tuberculosis.

Tuberculosis and aging: a global health problem

Despite the World Health Organization's declaration that the spread of tuberculosis is a global emergency and despite the implementation of strong tuberculosis-control initiatives, this highly infectious disease continues to affect all vulnerable populations, including the elderly population (age > or =65 years). Tuberculosis in aging adults remains a clinical and epidemiological challenge. Atypical clinical manifestations of tuberculosis in older persons can result in delay in diagnosis and initiation of treatment; thus, unfortunately, higher rates of morbidity and mortality from this treatable infection can occur. Underlying illnesses, age-related diminution in immune function, the increased frequency of adverse drug reactions, and institutionalization can complicate the overall clinical approach to tuberculosis in elderly patients; maintenance of a high index of suspicion for tuberculosis in this vulnerable population is, thus, undoubtedly justifiable.

MicroRNA 26a (miR-26a)/KLF4 and CREB-C/EBPβ regulate innate immune signaling, the polarization of macrophages and the trafficking of Mycobacterium tuberculosis to lysosomes during infection

For efficient clearance of Mycobacterium tuberculosis (Mtb), macrophages tilt towards M1 polarization leading to the activation of transcription factors associated with the production of antibacterial effector molecules such as nitric oxide (NO) and proinflammatory cytokines such as interleukin 1 β (IL-1β) and tumor necrosis factor α (TNF-α). At the same time, resolution of inflammation is associated with M2 polarization with increased production of arginase and cytokines such as IL-10. The transcriptional and post-transcriptional mechanisms that govern the balance between M1 and M2 polarization, and bacteria-containing processes such as autophagy and trafficking of Mtb to lysosomes, are incompletely understood. Here we report for the first time, that the transcription factor KLF4 is targeted by microRNA-26a (miR-26a). During Mtb infection, downregulation of miR-26a (observed both ex vivo and in vivo) facilitates upregulation of KLF4 which in turn favors increased arginase and decreased iNOS activity. We further demonstrate that KLF4 prevents trafficking of Mtb to lysosomes. The CREB-C/EBPβ signaling axis also favors M2 polarization. Downregulation of miR-26a and upregulation of C/ebpbeta were observed both in infected macrophages as well as in infected mice. Knockdown of C/ebpbeta repressed the expression of selected M2 markers such as Il10 and Irf4 in infected macrophages. The importance of these pathways is substantiated by observations that expression of miR-26a mimic or knockdown of Klf4 or Creb or C/ebpbeta, attenuated the survival of Mtb in macrophages. Taken together, our results attribute crucial roles for the miR-26a/KLF4 and CREB-C/EBPβsignaling pathways in regulating the survival of Mtb in macrophages. These studies expand our understanding of how Mtb hijacks host signaling pathways to survive in macrophages, and open up new exploratory avenues for host-targeted interventions.

Paradoxical worsening of tuberculosis in HIV-infected persons

OBJECTIVE

To determine the incidence of paradoxical worsening of tuberculosis (TB) in HIV-infected persons.

DESIGN

Observational cohort study.

SETTING

Public, urban TB clinic.

PATIENTS

HIV-infected persons treated for TB between January 1, 1996, and December 31, 1999, and followed through June 30, 2000.

INTERVENTION

Patients received standard anti-TB therapy. Antiretroviral therapy was provided by primary medical providers. Patients receiving antiretroviral therapy were given nucleoside reverse transcriptase inhibitors alone or highly active antiretroviral therapy (HAART; nucleoside reverse transcriptase inhibitors in combination with a protease inhibitor or a nonnucleoside reverse transcriptase inhibitor).

MAIN OUTCOME MEASURE

Paradoxical worsening of TB.

RESULTS

There were 82 TB cases in 76 patients. Paradoxical worsening was identified in 6 of 82 cases (7%; 95% confidence interval, 3 to 15%). Paradoxical worsening occurred in 3 of 28 cases (11%) in patients receiving HAART and in 3 of 44 cases (7%) in patients not receiving antiretroviral therapy (p = 0.67). Cases complicated by paradoxical worsening were more likely to have both pulmonary and extrapulmonary disease at initial diagnosis than cases without paradoxical worsening (83% vs 24%; p = 0.006). TB relapse occurred in 2 of 6 cases (33%) in patients with paradoxical worsening and in 4 of 76 cases (5%) in patients without paradoxical worsening (p = 0.06).

CONCLUSIONS

Paradoxical worsening of TB occurred less frequently than in previous reports and was not associated with HAART. Paradoxical worsening also appeared to be associated with an increased risk of TB relapse. Further studies are warranted to better characterize the risk factors for paradoxical worsening and the appropriate duration of anti-TB therapy in patients in whom it occurs.

Induction of ER stress in macrophages of tuberculosis granulomas

BACKGROUND

The endoplasmic reticulum (ER) stress pathway known as the Unfolded Protein Response (UPR) is an adaptive survival pathway that protects cells from the buildup of misfolded proteins, but under certain circumstances it can lead to apoptosis. ER stress has been causally associated with macrophage apoptosis in advanced atherosclerosis of mice and humans. Because atherosclerosis shares certain features with tuberculosis (TB) with regard to lesional macrophage accumulation, foam cell formation, and apoptosis, we investigated if the ER stress pathway is activated during TB infection.

PRINCIPAL FINDINGS

Here we show that ER stress markers such as C/EBP homologous protein (CHOP; also known as GADD153), phosphorylated inositol-requiring enzyme 1 alpha (Ire1α) and eukaryotic initiation factor 2 alpha (eIF2α), and activating transcription factor 3 (ATF3) are expressed in macrophage-rich areas of granulomas in lungs of mice infected with virulent Mycobacterium tuberculosis (Mtb). These areas were also positive for numerous apoptotic cells as assayed by TUNEL. Microarray analysis of human caseous TB granulomas isolated by laser capture microdissection reveal that 73% of genes involved in the UPR are upregulated at the mRNA transcript level. The expression of two ER stress markers, ATF3 and CHOP, were also increased in macrophages of human TB granulomas when assayed by immunohistochemistry. CHOP has been causally associated with ER stress-induced macrophage apoptosis. We found that apoptosis was more abundant in granulomas as compared to non-granulomatous tissue isolated from patients with pulmonary TB, and apoptosis correlated with CHOP expression in areas surrounding the centralized areas of caseation.

CONCLUSIONS

In summary, ER stress is induced in macrophages of TB granulomas in areas where apoptotic cells accumulate in mice and humans. Although macrophage apoptosis is generally thought to be beneficial in initially protecting the host from Mtb infection, death of infected macrophages in advanced granulomas might favor dissemination of the bacteria. Therefore future work is needed to determine if ER-stress is causative for apoptosis and plays a role in the host response to infection.

Lack of weight gain and relapse risk in a large tuberculosis treatment trial

BACKGROUND

Readily identified markers of tuberculosis relapse risk are needed, particularly in resource-limited settings. The association between weight gain or loss during antituberculosis therapy and relapse has not been well studied.

METHODS

Subjects in the Tuberculosis Trials Consortium Study 22 were studied. Underweight was defined as 10% or more below ideal body weight at diagnosis. Weight change was assessed between (1) diagnosis and completion of induction phase therapy, (2) diagnosis and end of continuation phase therapy, and (3) completion of induction to completion of continuation phase therapy.

RESULTS

A total of 857 subjects were monitored for 2 yr, and 61 of 857 (7.1%) relapsed. Relapse risk was high among persons who were underweight at diagnosis (19.1 vs. 4.8%; p < 0.001) or who had a body mass index of less than 18.5 kg/m(2) (19.5 vs. 5.8%; p < 0.001). Among persons who were underweight at diagnosis, weight gain of 5% or less between diagnosis and completion of 2-mo intensive phase therapy was moderately associated with an increased relapse risk (18.4 vs. 10.3%; relative risk, 1.79, 95% confidence interval, 0.96-3.32; p = 0.06). In a multivariate logistic regression model that was adjusted for other risk factors, a weight gain of 5% or less between diagnosis and completion of 2-mo intensive phase therapy among persons underweight at diagnosis was significantly associated with relapse risk (odds ratio, 2.4; p = 0.03).

CONCLUSIONS

Among persons underweight at diagnosis, weight gain of 5% or less during the first 2 mo of treatment is associated with an increased relapse risk. Such high-risk patients can be easily identified, even in resource-poor settings. Additional studies are warranted to identify interventions to decrease risk of relapse in such patients.

Association between Mycobacterium tuberculosis Beijing/W lineage strain infection and extrathoracic tuberculosis: Insights from epidemiologic and clinical characterization of the three principal genetic groups of M. tuberculosis clinical isolates

Clinical strains of Mycobacterium tuberculosis can be divided into three principal genetic groups based on the single-nucleotide polymorphisms at the katG gene codon 463 and the gyrA gene codon 95. One subgroup of genetic group 1, the Beijing/W lineage, has been widely studied because of its worldwide distribution and association with outbreaks. In order to increase our understanding of the clinical and epidemiological relevance of the genetic grouping of M. tuberculosis clinical strains and the Beijing/W lineage, we investigated the genetic grouping of 679 clinical isolates of M. tuberculosis, representing 96.3% of culture-confirmed tuberculosis cases diagnosed in Arkansas between January 1996 and December 2000 using PCR and DNA sequencing. We assessed the associations of infections by different genetic groups of M. tuberculosis strains and infection by the Beijing/W lineage strains with the clinical and epidemiological characteristics of the patients using chi-square tests and multivariate logistic regression analysis. Of the 679 study isolates, 676 fell into one of the three principal genetic groups, with 63 (9.3%) in group 1, 438 (64.8%) in group 2, and 175 (25.9%) in group 3. After adjusting for potential confounding of age, gender, race/ethnicity, human immunodeficiency virus serostatus, and plcD genotype in a multivariate logistic regression model, patients infected by the Beijing/W lineage isolates were nearly three times as likely as patients infected with the non-Beijing/W lineage isolates to have an extrathoracic involvement (odds ratio [95% confidence interval], 2.85 [1.33, 6.12]). Thus, the Beijing/W lineage strains may have some special biological features that facilitate the development of extrathoracic tuberculosis.