Local role for tumor necrosis factor alpha in the pulmonary inflammatory response to Mycobacterium tuberculosis infection

Heterogeneity in immune cell composition is associated with Mycobacterium tuberculosis replication at the granuloma level

The control of bacterial growth is key to the prevention and treatment of tuberculosis (TB). Granulomas represent independent foci of the host immune response that present heterogeneous capacity for control of bacterial growth. At the whole tissue level, B cells and CD4 or CD8 T cells have an established role in immune protection against TB. Immune cells interact within each granuloma response, but the impact of granuloma immune composition on bacterial replication remains unknown. Here we investigate the associations between immune cell composition, including B cell, CD4, and CD8 T cells, and the state of replicating Mycobacterium tuberculosis (Mtb) within the granuloma. A measure of ribosomal RNA synthesis, the RS ratio®, represents a proxy measure of Mtb replication at the whole tissue level. We adapted the RS ratio through use of in situ hybridization, to identify replicating and non-replicating Mtb within each designated granuloma. We applied a regression model to characterize the associations between immune cell populations and the state of Mtb replication within each respective granuloma. In the evaluation of nearly 200 granulomas, we identified heterogeneity in both immune cell composition and proportion of replicating bacteria. We found clear evidence of directional associations between immune cell composition and replicating Mtb. Controlling for vaccination status and endpoint post-infection, granulomas with lower CD4 or higher CD8 cell counts are associated with a higher percent of replicating Mtb. Conversely, changes in B cell proportions were associated with little change in Mtb replication. This study establishes heterogeneity across granulomas, demonstrating that certain immune cell types are differentially associated with control of Mtb replication. These data suggest that evaluation at the granuloma level may be imperative to identifying correlates of immune protection.

Mycobacterium tuberculosis PPE32 promotes cytokines production and host cell apoptosis through caspase cascade accompanying with enhanced ER stress response

Tuberculosis, caused by Mycobacterium tuberculosis (MTB) infection, remains a grave global public health burden which claims the lives around two to three million annually. PE and PPE proteins, featured by the Pro-Glu (PE) or Pro-Pro-Glu (PPE) motifs at the conserved N-terminal domain, are abundant in the MTB genome. PPE32 can increase intracellular survival of mycobacteria through abnormally increase in cytokines production. PPE32 might subvert the macrophage immune response and thwart its bactericidal effect. THP-1 macrophages treated with PPE32 or infected with Mycobacterium smegmatis (MS) expression PPE32 showed increase of cytokines production and multiple hallmarks of apoptosis. We found that PPE32 significantly increases the expression of IL-12p40 and IL-32 through ERK1/2 signaling pathway. In addition, the cell viability of macrophage was inhibited after PPE32 stimulation. We noted that PPE32 induces cleavage of caspase-3 and caspase-9, while inhibition of caspase activity significantly abrogates the PPE32-induced cell apoptosis. Moreover, PPE32 treatment promotes endoplasmic reticulum stress related gene expression, suggesting ER stress might be responsible for PPE32-induced cell apoptosis.

Leukocyte-specific protein 1 regulates neutrophil recruitment in acute lung inflammation

The mechanisms of excessive migration of activated neutrophils into inflamed lungs, credited with tissue damage, are not fully understood. We explored the hitherto unknown expression of leukocyte-specific protein 1 (LSP1) in human and mouse lungs and neutrophils and examined its role in neutrophil migration in acute lung inflammation. Autopsied septic human lungs showed increased LSP1 labeling in epithelium, endothelium, and leukocytes, including in their nuclei compared with normal lungs. We induced acute lung inflammation through intranasal administration of E. coli lipopolysaccharide (LPS) (80 μg) in LSP1-deficient (Lsp1(-/-)) and wild-type (WT) 129/SvJ mice. Immunocytochemistry and Western blots showed increased expression of LSP1 and phosphorylated LSP1 in lungs of LPS-treated WT mice. Histology showed more congestion, inflammation, and Gr-1(+) neutrophils in lung of WT mice than Lsp1(-/-) mice. LPS-treated WT mice had significantly more neutrophils in bronchoalveolar lavage (BAL) and myeloperoxidase levels in lungs compared with Lsp1(-/-) mice. However, there were no differences in lung tissue and BAL concentrations of keratinocyte-derived chemokine, monocyte chemoattractant protein-1, macrophage inflammatory protein-1α and -1β, vascular permeability, and phosphorylated p38 MAPK between LPS-treated WT and Lsp1(-/-) mice, whereas TNF-α concentration was higher in BAL fluid from LPS-treated WT. Immunoelectron microscopy showed increased LSP1 in the nuclei of LPS-treated neutrophils. We also found increased levels of phosphorylated LSP1 associated with plasma membrane, nucleus, and cytosol at various times after LPS treatment of murine bone marrow-derived neutrophils, suggesting its role in modulation of neutrophil cytoskeleton and the membrane. These data collectively show increased expression of LSP1 in inflamed mouse and human lungs and its role in neutrophil recruitment and lung inflammation.

Pulmonary tuberculosis in Asian elephants (Elephas maximus): histologic lesions with correlation to local immune responses

Although Mycobacterium tuberculosis infection is an important health concern for Asian elephants (Elephas maximus), no studies have evaluated the associated local immune responses or histologic lesions. In primates including humans, latent tuberculosis is distinguished by well-organized granulomas with TH1 cytokine expression, whereas active disease is characterized by poorly organized inflammation and local imbalance in TH1/TH2 cytokines. This study examined archival, formalin-fixed, paraffin-embedded lung samples from 5 tuberculosis-negative and 9 tuberculosis-positive Asian elephants. Lesions were assessed by light microscopy, and lymphoid infiltrates were characterized by CD3 and CD20 immunolabeling. Expression of TH1 (interferon [IFN]-γ, tumor necrosis factor [TNF]-α) and TH2 (interleukin [IL]-4, IL-10, transforming growth factor [TGF]-β) cytokines was determined using in situ hybridization. In 6 of 9 samples, inflammation was similar to the pattern of primate active disease with low to moderate numbers of lymphocytes, most of which were CD20 positive. In 1 sample, inflammation was most similar to latent tuberculosis in primates with numerous CD3-positive lymphocytes. Expression of IFN-γ was detected in 3 of 8 tuberculosis-positive samples. Expression of TNF-α was detected in 3 of 8 positive samples, including the one with latent morphology. Low-level expression of IL-4 was present in 4 of 8 positive samples. Only single positive samples displayed expression of IL-10 and TGF-β. Tuberculosis-negative samples generally lacked cytokine expression. Results showed heterogeneity in lesions of elephant tuberculosis similar to those of latent and active disease in primates, with variable expression of both TH1 and TH2 cytokines.

Long-term (postnatal day 70) outcome and safety of intratracheal transplantation of human umbilical cord blood-derived mesenchymal stem cells in neonatal hyperoxic lung injury

PURPOSE

This study was performed to evaluate the long-term effects and safety of intratracheal (IT) transplantation of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) in neonatal hyperoxic lung injury at postnatal day (P)70 in a rat model.

MATERIALS AND METHODS

Newborn Sprague Dawley rat pups were subjected to 14 days of hyperoxia (90% oxygen) within 10 hours after birth and allowed to recover at room air until sacrificed at P70. In the transplantation groups, hUCB-MSCs (5×10⁵) were administered intratracheally at P5. At P70, various organs including the heart, lung, liver, and spleen were histologically examined, and the harvested lungs were assessed for morphometric analyses of alveolarization. ED-1, von Willebrand factor, and human-specific nuclear mitotic apparatus protein (NuMA) staining in the lungs and the hematologic profile of blood were evaluated.

RESULTS

Impaired alveolar and vascular growth, which evidenced by an increased mean linear intercept and decreased amount of von Willebrand factor, respectively, and the hyperoxia-induced inflammatory responses, as evidenced by inflammatory foci and ED-1 positive alveolar macrophages, were attenuated in the P70 rat lungs by IT transplantation of hUCB-MSCs. Although rare, donor cells with human specific NuMA staining were persistently present in the P70 rat lungs. There were no gross or microscopic abnormal findings in the heart, liver, or spleen, related to the MSCs transplantation.

CONCLUSION

The protective and beneficial effects of IT transplantation of hUCB-MSCs in neonatal hyperoxic lung injuries were sustained for a prolonged recovery period without any long-term adverse effects up to P70.

The transcription factor NFATp plays a key role in susceptibility to TB in mice

In T cells, the transcription factor nuclear factor of activated T cells p (NFATp) is a key regulator of the cytokine genes tumor necrosis factor (TNF) and interferon-γ (IFN-γ). Here, we show that NFATp-deficient (NFATp(-/-)) mice have a dramatic and highly significant increase in mortality after Mycobacterium tuberculosis (MTb) infection as compared to mortality of control animals after MTb infection. Animals deficient in NFATp have significantly impaired levels of TNF and IFN-γ transcription and protein expression in naïve or total CD4(+) T cells, but display wild-type levels of TNF mRNA or protein from MTb-stimulated dendritic cells (DC). The rapid mortality and disease severity observed in MTb-infected NFATp(-/-) mice is associated with dysregulated production of TNF and IFN-γ in the lungs, as well as with increased levels of TNF, in their serum. Furthermore, global blocking of TNF production by injection of a TNF neutralizaing agent at 6 weeks, but not 12 weeks, post-MTb-infection further decreased the survival rate of both wild-type and NFATp(-/-) mice, indicating an early role for TNF derived from cells from the monocyte lineage in containment of infection. These results thus demonstrate that NFATp plays a critical role in immune containment of TB disease in vivo, through the NFATp-dependent expression of TNF and IFN-γ in T cells.

Reactivation of M. tuberculosis infection in trans-membrane tumour necrosis factor mice

Of those individuals who are infected with M. tuberculosis, 90% do not develop active disease and represents a large reservoir of M. tuberculosis with the potential for reactivation of infection. Sustained TNF expression is required for containment of persistent infection and TNF neutralization leads to tuberculosis reactivation. In this study, we investigated the contribution of soluble TNF (solTNF) and transmembrane TNF (Tm-TNF) in immune responses generated against reactivating tuberculosis. In a chemotherapy induced tuberculosis reactivation model, mice were challenged by aerosol inhalation infection with low dose M. tuberculosis for three weeks to establish infection followed chemotherapeutic treatment for six weeks, after which therapy was terminated and tuberculosis reactivation investigated. We demonstrate that complete absence of TNF results in host susceptibility to M. tuberculosis reactivation in the presence of established mycobacteria-specific adaptive immunity with mice displaying unrestricted bacilli growth and diffused granuloma structures compared to WT control mice. Interestingly, bacterial re-emergence is contained in Tm-TNF mice during the initial phases of tuberculosis reactivation, indicating that Tm-TNF sustains immune pressure as in WT mice. However, Tm-TNF mice show susceptibility to long term M. tuberculosis reactivation associated with uncontrolled influx of leukocytes in the lungs and reduced IL-12p70, IFNγ and IL-10, enlarged granuloma structures, and failure to contain mycobacterial replication relative to WT mice. In conclusion, we demonstrate that both solTNF and Tm-TNF are required for maintaining immune pressure to contain reactivating M. tuberculosis bacilli even after mycobacteria-specific immunity has been established.

Tumor necrosis factor alpha and high sensitivity C-reactive protein in diagnosis of exudative pleural effusion

BACKGROUND

Differentiation between exudative and transudative pleural effusions is the initial step in assessment of pleural effusion. The aim of this study was to determine whether high sensitivity C-reactive protein (hsCRP) and tumor necrosis factor α (TNFα) are diagnostic utilities for exudative pleural effusion.

METHODS

This experimental study assessed 79 patients with pleural effusion who underwent diagnostic evaluations at Imam Reza hospital, Mashhad, Iran in 2009-2010. The complete biochemical analysis of pleural fluid, pleural fluid culture, and pathological examination of pleural fluid and tissue were performed. Moreover, hsCRP and TNFα concentrations were measured in pleural fluid samples. The data was analyzed by student's t-test and Mann-Whitney test.

RESULTS

According to Light's criteria, 50 patients (63.30%) had exudative effusions while 29 subjects (36.70%) had transudative effusion. The pleural fluid concentrations of hsCRP and TNFα were significantly higher in the exudative group than the transudative group (p < 0.05). At a cutoff value of 5 mg/L for hsCRP, the results showed 94% sensitivity and 96.6% specificity. Regarding TNFα, a cutoff value of 12.9 ng/dl represented 96% sensitivity and 93% specificity.

CONCLUSIONS

HsCRP and TNFα levels may be considered as beneficial diagnostic factors for detecting exudative effusion in patients with pleural effusion.

Latency antigen α-crystallin based vaccination imparts a robust protection against TB by modulating the dynamics of pulmonary cytokines

Background

Efficient control of tuberculosis (TB) requires development of strategies that can enhance efficacy of the existing vaccine Mycobacterium bovis Bacille Calmette Guerin (BCG). To date only a few studies have explored the potential of latency-associated antigens to augment the immunogenicity of BCG.

Methods/Principal Findings

We evaluated the protective efficacy of a heterologous prime boost approach based on recombinant BCG and DNA vaccines targeting α-crystallin, a prominent latency antigen. We show that “rBCG prime - DNA boost” strategy (R/D) confers a markedly superior protection along with reduced pathology in comparison to BCG vaccination in guinea pigs (565 fold and 45 fold reduced CFU in lungs and spleen, respectively, in comparison to BCG vaccination). In addition, R/D regimen also confers enhanced protection in mice. Our results in guinea pig model show a distinct association of enhanced protection with an increased level of interleukin (IL)12 and a simultaneous increase in immuno-regulatory cytokines such as transforming growth factor (TGF)β and IL10 in lungs. The T cell effector functions, which could not be measured in guinea pigs due to technical limitations, were characterized in mice by multi-parameter flow cytometry. We show that R/D regimen elicits a heightened multi-functional CD4 Th1 cell response leading to enhanced protection.

Conclusions/Significance

These results clearly indicate the superiority of α-crystallin based R/D regimen over BCG. Our observations from guinea pig studies indicate a crucial role of IL12, IL10 and TGFβ in vaccine-induced protection. Further, characterization of T cell responses in mice demonstrates that protection against TB is predictable by the frequency of CD4 T cells simultaneously producing interferon (IFN)γ, tumor necrosis factor (TNF)α and IL2. We anticipate that this study will not only contribute toward the development of a superior alternative to BCG, but will also stimulate designing of TB vaccines based on latency antigens.

IL-32 is a host protective cytokine against Mycobacterium tuberculosis in differentiated THP-1 human macrophages

Macrophages provide a first line of defense against Mycobacterium tuberculosis. However, in instances where macrophage activation for killing is suboptimal, M. tuberculosis is capable of surviving intracellularly. IL-32 is a recently described cytokine induced by M. tuberculosis in a variety of cell types including human monocytes and macrophages. In this study, we investigated the biological significance of IL-32 in an in vitro model of M. tuberculosis infection in differentiated THP-1 human macrophages in which IL-32 expression was silenced using stable expression of short hairpin RNA (shRNA). Inhibition of endogenous IL-32 production in THP-1 cells that express one of three distinct shRNA-IL-32 constructs significantly decreased M. tuberculosis induction of TNF-alpha by approximately 60%, IL-1beta by 30-60%, and IL-8 by 40-50% and concomitantly increased the number of cell-associated M. tuberculosis bacteria compared with THP-1 cells stably expressing a scrambled shRNA. In THP-1 cells infected with M. tuberculosis and stimulated with rIL-32, a greater level of apoptosis was observed compared with that with M. tuberculosis infection alone. Obversely, there was significant abrogation of apoptosis induced by M. tuberculosis and a concomitant decrease in caspase-3 activation in cells depleted of endogenous IL-32. rIL-32gamma significantly reduced the number of viable intracellular M. tuberculosis bacteria, which was modestly but significantly abrogated with a caspase-3 inhibitor. We conclude that IL-32 plays a host defense role against M. tuberculosis in differentiated THP-1 human macrophages.

Histamine plays an essential regulatory role in lung inflammation and protective immunity in the acute phase of Mycobacterium tuberculosis infection

The course and outcome of infection with mycobacteria are determined by a complex interplay between the immune system of the host and the survival mechanisms developed by the bacilli. Recent data suggest a regulatory role of histamine not only in the innate but also in the adaptive immune response. We used a model of pulmonary Mycobacterium tuberculosis infection in histamine-deficient mice lacking histidine decarboxylase (HDC(-/-)), the histamine-synthesizing enzyme. To confirm that mycobacterial infection induced histamine production, we exposed mice to M. tuberculosis and compared responses in C57BL/6 (wild-type) and HDC(-/-) mice. Histamine levels increased around fivefold above baseline in infected C57BL/6 mice at day 28 of infection, whereas only small amounts were detected in the lungs of infected HDC(-/-) mice. Blocking histamine production decreased both neutrophil influx into lung tissue and the release of proinflammatory mediators, such as interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-alpha), in the acute phase of infection. However, the accumulation and activation of CD4(+) T cells were augmented in the lungs of infected HDC(-/-) mice and correlated with a distinct granuloma formation that contained abundant lymphocytic infiltration and reduced numbers of mycobacteria 28 days after infection. Furthermore, the production of IL-12, gamma interferon, and nitric oxide, as well as CD11c(+) cell influx into the lungs of infected HDC(-/-) mice, was increased. These findings indicate that histamine produced after M. tuberculosis infection may play a regulatory role not only by enhancing the pulmonary neutrophilia and production of IL-6 and TNF-alpha but also by impairing the protective Th1 response, which ultimately restricts mycobacterial growth.

Lymphotoxin-alpha and TNF have essential but independent roles in the evolution of the granulomatous response in experimental leprosy

Recent studies identified an association between genetic variants in the lymphotoxin-alpha (LTalpha) gene and leprosy. To study the influence of LTalpha on the control of experimental leprosy, both low- and high-dose Mycobacterium leprae foot pad (FP) infections were evaluated in LTalpha-deficient chimeric (cLTalpha(-/-)) and control chimeric (cB6) mice. Cellular responses to low-dose infection in cLTalpha(-/-) mice were dramatically different, with reduced accumulation of CD4(+) and CD8(+) lymphocytes and macrophages and failure to form granulomas. Growth of M. leprae was contained for 6 months, but augmented late in infection. In contrast, tumor necrosis factor knockout and tumor necrosis factor receptor 1 knockout FPs exhibited extensive inflammatory infiltration with an increase in M. leprae growth throughout infection. Following high-dose infection, cB6 FP induration peaked at 4 weeks and was maintained for 12 weeks. Induration was not sustained in cLTalpha(-/-) FPs that contained few lymphocytes and no granulomas. There was a reduction in the expression levels of inflammatory cytokines, chemokines, and chemokine receptors, including nitric oxide synthase 2, vascular cell adhesion molecule, and intercellular cell adhesion molecule. Furthermore, cLTalpha(-/-) popliteal lymph nodes contained a higher proportion of naïve CD44(lo)CD62L(hi) T cells than cB6 mice, suggestive of reduced T cell activation. Therefore, both LTalpha and tumor necrosis factor are essential for the regulation of the granuloma, but they have distinctive roles in the recruitment of lymphocytes and maintenance of the granulomatous response during chronic M. leprae infection.

Tumor necrosis factor signaling mediates resistance to mycobacteria by inhibiting bacterial growth and macrophage death

Tumor necrosis factor (TNF), a key effector in controlling tuberculosis, is thought to exert protection by directing formation of granulomas, organized aggregates of macrophages and other immune cells. Loss of TNF signaling causes progression of tuberculosis in humans, and the increased mortality of Mycobacterium tuberculosis-infected mice is associated with disorganized necrotic granulomas, although the precise roles of TNF signaling preceding this endpoint remain undefined. We monitored transparent Mycobacterium marinum-infected zebrafish live to conduct a stepwise dissection of how TNF signaling operates in mycobacterial pathogenesis. We found that loss of TNF signaling caused increased mortality even when only innate immunity was operant. In the absence of TNF, intracellular bacterial growth and granuloma formation were accelerated and was followed by necrotic death of overladen macrophages and granuloma breakdown. Thus, TNF is not required for tuberculous granuloma formation, but maintains granuloma integrity indirectly by restricting mycobacterial growth within macrophages and preventing their necrosis.

Acute phase markers for the differentiation of infectious and malignant pleural effusions

Acute-phase markers, such as C-reactive protein (CRP), interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-alpha), have been studied in inflammatory and malignant disorders. We examined the diagnostic value of these markers for the differentiation among parapneumonic, tuberculous and malignant effusions. We studied 124 patients with pleural effusions, classified as exudates [total (n=97), parapneumonic (n=15), tuberculous (n=25), malignant (n=57)] and transudates due to congestive heart failure (n=27). CRP, IL-6 and TNF-alpha were measured in pleural fluid and serum. Pleural fluid CRP was higher in parapneumonic compared to tuberculous and malignant effusions, providing 100% sensitivity for a cut-off point of 5.3mg/dL. IL-6 was higher in both parapneumonic and tuberculous compared to malignant effusions. TNF-alpha was higher in tuberculous compared to malignant effusions, providing 96.0% sensitivity, and 93.0% specificity for a cut-off point of 88.1 pg/mL. Pleural fluid CRP levels were lower than serum in all groups, probably reflecting systemic inflammation, whereas IL-6 and TNF-alpha were higher in pleural fluid indicating local production. Our data suggest that these markers may provide useful information for the differentiation of infectious and malignant effusions in clinical practice. However, further studies are needed for the validation of these findings in usual clinical circumstances.

Microdissection of the cytokine milieu of pulmonary granulomas from tuberculous guinea pigs

Levels of IL-12p40, TNFalpha, TGFbeta, IFNgamma and IL-10 mRNA were assessed by laser capture microdissection followed by quantitative real-time PCR in the pulmonary granulomas of unimmunized and BCG-vaccinated guinea pigs infected by aerosol with virulent Mycobacterium tuberculosis. Lesions microdissected from unimmunized guinea pigs were overwhelmed by the pro-inflammatory TNFalpha mRNA at both 3 and 6 weeks post infection, indicating the struggle to control the mounting infection. The cytokine profile of granulomas from vaccinated guinea pigs shifted from type 1 cytokine mRNA (IFNgamma and IL-12p40) at 3 weeks to a predominantly anti-inflammatory environment (TGFbeta mRNA) at 6 weeks. The relative proportions of cytokine mRNA transcripts in the periphery of the granuloma were different from the centre, reflecting differences in cell composition and architecture. Moreover, analysis of the individual lung lobes at 6 weeks post infection suggests that heterogeneity exists in the cytokine profile between the lobes of the lung.

Role of mast cells as IL10 producing cells in paracoccidioidomycosis skin lesions

Recent works have demonstrated that mast cells may have an important role in immunologic reactions and inflammation once they synthesize and secrete many cytokines including IL4, IL5, IL6 and TNF-alpha. We have conducted research in order to verify if mast cells would participate in the local inflammatory immune response against Paracoccidioides brasiliensis in skin lesions characterized by a Th2 pattern of cytokines. Fifty-nine skin biopsies with previous histopathological diagnosis of paracoccidioidomycosis and immunohistochemical characterization of cytokines present in the inflammatory infiltrate were classified in three groups: group 1 (G1), with compact granuloma and a Th1 pattern of cytokines; group 2 (G2), with loose granuloma and a Th2 pattern of cytokines; group 3 (G3), both kind of granuloma in the same lesion, characterized by cytokines from Th1 and Th2 patterns. Ten biopsies from normal skin were used as control group. Mast cells were visualized and quantified by a toluidine blue/HCl staining and a double immunostaining was performed to detect a co-localization of mast cells and IL10. G2 presented an increased number of mast cells when compared to G1, G3 and control group and we frequently could find mast cells expressing IL10 in G2. The data obtained suggest that mast cells participate in the immune response against P. brasiliensis in skin lesions with loose granuloma and a Th2 pattern of cytokines. Considering these results, mast cells could constitute a source of IL10, contributing to a non-effective response against fungal antigens.

Elevated serum CCL2 concomitant with a reduced mycobacterium-induced response leads to disease dissemination in leprosy

Mycobacterium leprae and Mycobacterium tuberculosis are successful intracellular pathogens which down regulate host immune responses. T-cell interferon-gamma (IFNgamma) and macrophage tumour necrosis factor-alpha (TNFalpha) activate chemokines such as, C-C chemokine ligand-2 (CCL2) and CCL5, which play a role in granuloma formation. Lepromatous leprosy is characterized by defective granulomas with lowered T-cell- and macrophage-mediated responses. Tuberculosis (TB) can be localized to the lung, whereby discreet granulomas are formed. The role of chemokines in leprosy infections is as yet unclear. We compared chemokine responses in lepromatous leprosy and pulmonary tuberculosis patients. Circulating serum CCL2 was raised while CCL5 was lowered in leprosy, as compared with TB patients and healthy controls. However, both Mycobacterium bovis BCG- (P=0.08) and M. leprae-induced (P=0.05) CCL2 secretion was reduced in leprosy. In leprosy, BCG induced greater CCL2 (P=0.01), TNFalpha (P=0.02) and somewhat greater CCL5 (P=0.08) than M. leprae, while CXCL8 induction was comparable. Overall levels of Mycobacterium-induced CCL2, TNFalpha and CXCL8 were two to threefold lower, and CCL5 was 10-fold lower in leprosy as compared with TB. Reduced inducible CCL2 combined with a lowered TNFalpha response in lepromatous leprosy may contribute to the unrestricted growth and dissemination of mycobacteria found in the disease.

Potential correlates of BCG induced protection against tuberculosis detected in a mouse aerosol model using gene expression profiling

Tuberculosis (TB) is responsible for more than 2 million deaths per year with the incidence of new cases rising throughout the world. Mycobacterium bovis bacillus Calmette Guerin (BCG) is currently the only available licensed vaccine against M. tuberculosis. Despite the variable protective efficacy in different populations it affords some protection, particularly against childhood and disseminated forms of the disease. BCG remains the gold standard for assessing other prospective TB vaccines, yet there is a lack of information on the mechanisms of BCG protection and consequently there are no definitive correlates of protection for this vaccine. In order to further studies in this area we assessed lung RNA homogenates from naïve, BCG vaccinated and aerosol challenged mice. We found increased IFN-gamma levels in lungs of aerosol challenged mice previously vaccinated with BCG and a number of transcripts regulated by IFN-gamma were also increased in the lungs of these animals. These transcripts represent a cluster of IFN-gamma related transcripts that may assist in determining if BCG and maybe other potential vaccines will elicit protection against M. tuberculosis.

NEUTRALIZATION OF TUMOR NECROSIS FACTOR IN PRECLINICAL MODELS OF SEPSIS

Tumor necrosis factor (TNFalpha), a cardinal early mediator of the innate host inflammatory response, has been an attractive target for therapeutic intervention in human sepsis. However, pooled data from 12 completed randomized controlled trials show only a very modest impact on mortality in a highly heterogeneous population of patients. To gain insight into the preclinical in vivo biology of TNFalpha that might aid in better identifying appropriate patient populations for therapeutic intervention, we undertook a systematic review of published reports of preclinical studies assessing the consequences of neutralization of TNFalpha in models of acute infection or inflammation. We identified 143 reports incorporating 484 unique experimental comparisons in seven different animal species. The effects of neutralization of TNFalpha in these were quite variable. Neutralization of TNFalpha was beneficial in endotoxemia, or after systemic challenge with gram-negative organisms, Staphylococcus aureus, or Group B streptococci. On the other hand, neutralization was detrimental in infections caused by Streptococcus pneumoniae, Candida spp., or intracellular pathogens such as Listeria and Mycobacterium tuberculosis, and in models of pneumonia. Treatment was more efficacious when delivered before infectious challenge, and the therapeutic signal increased as the baseline mortality in the placebo group increased. Evidence of neutralization of TNFalpha bioactivity, and of attenuation of inflammation, was typically accompanied by evidence of impairment of antimicrobial defenses. Multiple specific and nonspecific therapeutic strategies were identified. We conclude that the beneficial effects of TNF in systemic inflammation occur at the cost of impaired antimicrobial defenses, and that a better understanding of the consequences of neutralization of TNFalpha in vivo could aid in better defining optimal patient populations for therapeutic intervention.

Infections associated with tumor necrosis factor-alpha antagonists

Tumor necrosis factor (TNF)-alpha antagonists are promising therapeutic agents for patients with severe autoimmune and rheumatologic conditions. Unfortunately, their use has been associated with an increased rate of tuberculosis, endemic mycoses, and intracellular bacterial infections. Infliximab, 1 of 3 available drugs in this novel class, appears to be associated with the greatest risk of infection, likely because of its long half-life and induction of monocyte apoptosis. Prospective trials are necessary to determine the exact risk associated with these agents, particularly the newer TNF-alpha antagonists. More specific TNF-alpha blockers, which reduce inflammation while maintaining adequate immunity, are needed. In the meantime, a thorough work-up is mandatory for all febrile illness occurring in TNF-alpha blocker recipients. We present 4 patients who developed severe infections during TNF-alpha antagonist therapy, review the literature, and discuss current guidelines for surveillance and prophylaxis.

Elevated ex vivo monocyte chemotactic protein-1 (CCL2) in pulmonary as compared with extra-pulmonary tuberculosis

Background

Tuberculosis causes 3 million deaths annually. The most common site of tuberculosis is pulmonary however; extra-pulmonary forms of the disease also remain prevalent. Restriction of Mycobacterium tuberculosis depends on effective recruitment and subsequent activation of T lymphocytes, mononuclear and polymorphonuclear cells to the site of infection. Tumor necrosis factor (TNF)-α is essential for granuloma formation and is a potent activator of monocyte chemotactic protein (MCP-1, CCL2). CCL2 is essential for recruitment of monocytes and T cells and has been shown to play a role in protection against tuberculosis. Interleukin -8 (CXCL8) is a potent activator of neutrophils. Increased levels of CCL2, CXCL8 and TNFα are reported in tuberculosis but their significance in different forms of tuberculosis is as yet unclear. We have used an ex vivo assay to investigate differences in immune parameters in patients with either pulmonary or extra-pulmonary tuberculosis.

Methods

Serum levels of CCL2, CXCL8 and TNFα were measured in patients with pulmonary tuberculosis (N = 12), extra-pulmonary tuberculosis (N = 8) and BCG-vaccinated healthy volunteers (N = 12). Whole blood cells were stimulated with non-pathogenic Mycobacterium bovis bacille-Calmette Guerin (BCG) vaccine strain or bacterial lipopolysaccharide (LPS) and cyto/chemokines were monitored in supernatants.

Results

Circulating serum levels of CXCL8 and TNFα were raised in all tuberculosis patients, while CCL2 levels were not. There was no difference in spontaneous cytokine secretion from whole blood cells between patients and controls. M. bovis BCG-induced ex vivo CCL2 secretion was significantly greater in pulmonary as compared with both extra-pulmonary tuberculosis patients and endemic controls. In response to LPS stimulation, patients with pulmonary tuberculosis showed increased CCL2 and TNFα responses as compared with the extra-pulmonary group. BCG-, and LPS-induced CXCL8 secretion was comparable between patients and controls.

Conclusion

CCL2 is activated by TNFα and is essential for recruitment of monocytes and T cells to the site of mycobacterial infection. Increased CCL2 activation in pulmonary tuberculosis may result in a stronger cellular response as compared with extra-pulmonary tuberculosis patients, and this may contribute to the localization of infection to the pulmonary site.

Contribution of transmembrane tumor necrosis factor to host defense against Mycobacterium bovis bacillus Calmette-guerin and Mycobacterium tuberculosis infections

To study the specific role of transmembrane tumor necrosis factor (TmTNF) in host defense mechanisms against bacillus Calmette-Guerin (BCG) and Mycobacterium tuberculosis infections, we compared the immune responses of TNF/lymphotoxin (LT)-alpha(-/-) mice expressing a noncleavable transgenic TmTNF (TmTNF tg) to those of TNF/LT-alpha(-/-) and wild-type mice. Susceptibility of TNF/LT-alpha(-/-) mice to BCG infection was associated with impaired induction of systemic RANTES but not of monocyte chemoattractant protein 1 (MCP-1), the development of excessive local and systemic Th1-type immune responses, and a substantially reduced inducible nitric oxide synthase (iNOS) activity. Resistance of TmTNF tg mice to BCG infection was associated with efficient activation of iNOS in granulomas and with the regulated release of local and systemic chemokines and Th1-type cytokines. However, M. tuberculosis infection of TmTNF tg mice resulted in longer survival and enhanced resistance compared to TNF/LT-alpha(-/-) mice but higher sensitivity than wild-type mice. TmTNF tg mice exhibited reduced pulmonary iNOS expression and showed an exacerbated cellular infiltration in the lungs despite a modest bacillary content. Our data thus indicate a role for TmTNF in host defense against mycobacteria by contributing to induction and regulation of Th1-type cytokine and chemokine expression leading to development of bactericidal granulomas expressing iNOS, which critically determines susceptibility versus resistance of the host to mycobacterial infections.

Transmembrane TNF is sufficient to initiate cell migration and granuloma formation and provide acute, but not long-term, control of Mycobacterium tuberculosis infection

TNF is critical for immunity against Mycobacterium tuberculosis infection; however, the relative contributions of the soluble and transmembrane forms of TNF in this immunity are unknown. Using memTNF mice, which express only the transmembrane form of TNF, we have addressed this question. Wild-type (WT), TNF-/-, and transmembrane TNF (memTNF) mice were infected with M. tuberculosis by aerosol. TNF-/- mice developed overwhelming infection with extensive pulmonary necrosis and died after only 33 days. memTNF mice, like WT mice, contained bacterial growth for over 16 wk, developed an Ag-specific T cell response, and initially displayed compact granulomas, comprised of both lymphocytes and macrophages. Expression of mRNA for the chemokines CXCL10, CCL3, CCL5, and CCL7 was comparable in both WT and memTNF mice. As the infection progressed, however, the pulmonary lesions in memTNF mice became larger and more diffuse, with increased neutrophil accumulation and necrosis. This was accompanied by increased influx of activated memory T cells into the lungs of memTNF mice. Eventually, these mice succumbed to infection with a mean time to death of 170 days. The expression of memTNF on T cells is functionally important because the transfer of T cells from memTNF, but not TNF-/- mice, into either RAG-/- or TNF-/- mice conferred the same survival advantage on the M. tuberculosis-infected recipient mice, as the transfer of WT T cells. Therefore, memTNF, in the absence of soluble TNF, is sufficient to control acute, but not chronic, M. tuberculosis infection, in part through its expression on T cells.

IL-10-producing and naturally occurring CD4+ Tregs: limiting collateral damage

Effective immune responses against pathogens are sometimes accompanied by strong inflammatory reactions. To minimize damage to self, the activation of the immune system also triggers anti-inflammatory circuits. Both inflammatory and anti-inflammatory reactions are normal components of the same immune response, which coordinately fight infections while preventing immune pathology. IL-10 is an important suppressive cytokine, produced by a large number of immune cells in addition to the antigen-driven IL-10-producing regulatory and the naturally occurring suppressor CD4+ T cells, which is a key player in anti-inflammatory immune responses. However, additional mechanisms have evolved to ensure that pathogen eradication is achieved with minimum damage to the host. Here we discuss those mechanisms that operate to regulate effector immune responses.

Distribuição de Polimorfismos de Base única (SNPs) no gene de TNF-alfa (-238/-308) entre pacientes com TB e outras pneumopatias: marcadores genéticos de susceptibilidade a ocorrência de TB?

INTRODUÇÃO: Fatores genéticos podem desempenhar um importante papel na susceptibilidade à tuberculose (TB) ativa, e polimorfismos de base única (SNPs) em diferentes genes que codificam para citocinas têm sido descritos e associados com doenças. OBJETIVOS: Investigar o quanto polimorfismo na região promotora do gene que codifica para TNF-alfa (-238 e -308) estão associados a ocorrência de TB ativa. MÉTODOS: SNPs dentro do gene de TNF-alfa foram analisados por PCR- RFLP em dois grupos de indivíduos: pacientes com TB (n = 234) e pacientes com pneumopatias não TB (n = 113). RESULTADOS: Neste estudo, o alelo -238A esteve associado significantemente com susceptibilidade à ocorrência de TB e gravidade das formas clínicas (p = 0,00002; OR = 0,15; IC = 0,06-0,36). Por outro lado, o alelo -308A esteve associado significantemente com a proteção a outras formas de doença pulmonar (p = 0,02; OR = 1,95; IC = 1,07-3,58). CONCLUSÕES: Estes resultados preliminares sugerem a importância de estudos genéticos na ocorrência da TB. São necessários outros estudos para melhorar a compreensão sobre a patogênese do M. tb.

Individual RD1-region genes are required for export of ESAT-6/CFP-10 and for virulence of Mycobacterium tuberculosis

The RD1 genomic region is present in virulent strains of Mycobacterium tuberculosis (MTB), missing from the vaccine strain M. bovis BCG, and its importance to virulence has been established experimentally. Based on in silico analysis, it has been suggested that RD1 may encode a novel secretion system, but the mechanism by which this region affects virulence is unknown. Here we examined mutants disrupted in five individual RD1 genes. Both in vitro and in vivo, each mutant displayed an attenuated phenotype very similar to a mutant missing the entire RD1 region. Genetic complementation of individual genes restored virulence. Attenuated mutants could multiply within THP-1 cells, but they were unable to spread to uninfected macrophages. We also examined export of two immunodominant RD1 proteins, CFP-10 and ESAT-6. Export of these proteins was greatly reduced or abolished in each attenuated mutant. Again, genetic complementation restored a wild-type phenotype. Our results indicate that RD1 genes work together to form a single virulence determinant, and argue that RD1 encodes a novel specialized secretion system that is required for pathogenesis of MTB.

Respiratory epithelial cells regulate lung inflammation in response to inhaled endotoxin

To determine the role of respiratory epithelial cells in the inflammatory response to inhaled endotoxin, we selectively inhibited NF-kappa B activation in the respiratory epithelium using a mutant I kappa B-alpha construct that functioned as a dominant negative inhibitor of NF-kappa B translocation (dnI kappa B-alpha). We developed two lines of transgenic mice in which expression of dnI kappa B-alpha was targeted to the distal airway epithelium using the human surfactant apoprotein C promoter. Transgene expression was localized to the epithelium of the terminal bronchioles and alveoli. After inhalation of LPS, nuclear translocation of NF-kappa B was evident in bronchiolar epithelium of nontransgenic but not of transgenic mice. This defect was associated with impaired neutrophilic lung inflammation 4 h after LPS challenge and diminished levels of TNF-alpha, IL-1 beta, macrophage inflammatory protein-2, and KC in lung homogenates. Expression of TNF-alpha within bronchiolar epithelial cells and of VCAM-1 within peribronchiolar endothelial cells was reduced in transgenic animals. Thus targeted inhibition of NF-kappa B activation in distal airway epithelial cells impaired the inflammatory response to inhaled LPS. These data provide causal evidence that distal airway epithelial cells and the signals they transduce play a physiological role in lung inflammation in vivo.

The immunological aspects of latency in tuberculosis

A unique feature of Mycobacterium tuberculosis is its ability to exist in the granuloma of an asymptomatic host in a latent state that can subsequently reactivate to cause active disease. The latent state of infection poses a major obstacle to eradicating tuberculosis. In latent tuberculosis, the host immune response is capable of controlling the infection and yet falls short of eradicating the pathogen. That the host immune response contributes to the maintenance of latent tuberculous infection is supported by the observation that certain immunodeficient states, including those associated with the human immunodeficiency virus and tumor necrosis factor neutralization therapy, are associated with increased risks for developing reactivation disease. Latent tuberculosis is the product of a complex set of interactions between M. tuberculosis and the host immune response. The molecular basis for the persistence phenotype of M. Tuberculosis and the pertinent host immune mechanisms that contribute to the maintenance of tuberculous latency are just beginning to be understood. This review discusses the interactions between M. tuberculosis and the macrophage, the primary host cell that the tubercle bacillus parasitizes.

TNF-alpha is a critical negative regulator of type 1 immune activation during intracellular bacterial infection

TNF-alpha has long been regarded as a proimmune cytokine involved in antimicrobial type 1 immunity. However, the precise role of TNF-alpha in antimicrobial type 1 immunity remains poorly understood. We found that TNF-alpha-deficient (TNF(-/-)) mice quickly succumbed to respiratory failure following lung infection with replication-competent mycobacteria, because of apoptosis and necrosis of granuloma and lung structure. Tissue destruction was a result of an uncontrolled type 1 immune syndrome characterized by expansion of activated CD4 and CD8 T cells, increased frequency of antigen-specific T cells, and overproduction of IFN-gamma and IL-12. Depletion of CD4 and CD8 T cells decreased IFN-gamma levels, prevented granuloma and tissue necrosis, and prolonged the survival of TNF(-/-) hosts. Early reconstitution of TNF-alpha by gene transfer reduced the frequency of antigen-specific T cells and improved survival. TNF-alpha controlled type 1 immune activation at least in part by suppressing T cell proliferation, and this suppression involved both TNF receptor p55 and TNF receptor p75. Heightened type 1 immune activation also occurred in TNF(-/-) mice treated with dead mycobacteria, live replication-deficient mycobacteria, or mycobacterial cell wall components. Our study thus identifies TNF-alpha as a type 1 immunoregulatory cytokine whose primary role, different from those of other type 1 cytokines, is to keep an otherwise detrimental type 1 immune response in check.

Increased Dendritic Cell Numbers Impair Protective Immunity to Intracellular Bacteria Despite Augmenting Antigen-Specific CD8+T Lymphocyte Responses

Dendritic cells (DCs) reside in tissues, where they function as sentinels, providing an essential link between innate and adaptive immunity. Increasing the numbers of DCs in vivo augments T cell responses, and can cause dramatic CTL-dependent tumor regression. To determine whether greater DC numbers promoted T cell-mediated protection in the context of host defense against intracellular bacteria, we treated mice with Flt3 ligand (Flt3-L) to increase DCs in vivo and challenged them with Listeria monocytogenes. Unexpectedly, after primary challenge with Listeria, the overall control of Listeria infection was impaired in Flt3-L-treated mice, which had greater bacterial burden and mortality than controls. Similar results were obtained when DC numbers were increased by treatment with polyethylene glycol-conjugated GM-CSF rather than Flt3-L and in mice infected with Mycobacterium tuberculosis. Impaired protection was not due to dysfunctional T cell responses, as Flt3-L-treated mice had a greater frequency and absolute number of Ag-specific CD8+ T cells, which produced IFN-gamma, exhibited cytolytic activity, and transferred protection. The increased Listeria burden in Flt3-L-treated mice was preferentially associated with DCs, which were unable to kill Listeria and more resistant to CTL lysis compared with macrophages in vitro. Although we cannot exclude the possibility that other potential effects, in addition to increased numbers of DCs, are shared by Flt3-L and polyethylene glycol-conjugated GM-CSF and contributed to the increase in susceptibility observed in treated mice, these results support the notion that DC numbers must be properly controlled within physiological limits to optimize host defense to intracellular bacterial pathogens.

Regulation of monocyte chemokine and MMP-9 secretion by proinflammatory cytokines in tuberculous osteomyelitis

Tuberculous osteomyelitis causes bony destruction as a result of interactions among the pathogen, resident bone cells, and influxing leukocytes. Recruitment of monocytes and T cells is critical for antimycobacterial granuloma formation, but little is known about mechanisms regulating this in bone. We investigated the role of tumor necrosis factor alpha (TNF-alpha) and interleukin (IL)-1, key cytokines in granuloma formation, in networks involving human osteoblasts and monocytes. Experiments focused on CXC ligand (CXCL)8, CCL2, and matrix metalloproteinase (MMP)-9, human monocyte-derived mediators involved in control of leukocyte influx. TNF-alpha but not IL-1 has a key role stimulating CXCL8 secretion in Mycobacterium tuberculosis-infected human osteoblast MG-63 cells. Conditioned medium from M. tuberculosis-infected osteoblasts (COBTB) drives CXCL8 and some CCL2 gene expression and secretion from primary human monocytes. IL-1 receptor antagonist and to a lesser extent anti-TNF-alpha inhibited COBTB-induced CXCL8 secretion (P<0.01) but did not affect gene expression. IL-1 blockade had a comparatively lesser effect on CCL2 secretion, whereas anti-TNF decreased CCL2 concentrations from 7840 +/- 140 to 360 +/- 80 pg/ml/4 x 10(5) cells. Neither proinflammatory mediator affects MMP-9 secretion from COBTB-stimulated human monocytes. In summary, in a paracrine network, M. tuberculosis-infected osteoblasts drive high-level CXCL8, comparatively less CCL2, but do not alter MMP-9 secretion from uninfected human monocytes. This network is, in part, regulated by IL-1 and TNF-alpha.

The effect of mycobacterial virulence and viability on MAP kinase signalling and TNF alpha production by human monocytes

SETTING

The success of Mycobacterium tuberculosis as a human pathogen depends on its ability to tolerate and perhaps manipulate host defense mechanisms.

OBJECTIVE

To determine the induction of tumour necrosis factor-alpha (TNF alpha), a central mediator of immunity, by human monocytes infected with virulent M. tuberculosis, M. leprae and attenuated M. bovis BCG.

DESIGN

Mycobacteria-induced cellular activation pathways of TNF alpha production was investigated using an inhibitor of protein tyrosine kinase (PTKs) and an inhibitor of mitogen-activated protein (MAP) kinases.

RESULTS

TNF alpha production was significantly lower during infection with virulent M. tuberculosis than with BCG and this differential response was independent of mycobacterial viability. TNF alpha production involved the PTK and MAP kinase pathways. Reduced TNF alpha induction by M. tuberculosis was associated with a reduction in the extent and duration of phosphorylation of extracellular-signal regulated kinases (ERK 1/2). Infection with M. leprae triggered low and transient ERK 1/2 activation as well as low TNF alpha production.

CONCLUSION

Maintenance of the differential response in both live and heat-killed preparations suggests that the reduced TNF alpha response associated with virulent mycobacteria is due to differences in the presence of components capable of triggering host pattern recognition receptors, rather than events associated with phagosome trafficking or the active release of intracellular modulators.

Advances in antibody-mediated immunity againstMycobacterium tuberculosis: implications for a novel vaccine strategy

Cell-mediated immunity is considered to be the major component of the host response against Mycobacterium tuberculosis, whereas antibody-mediated immunity historically has been considered inconsequential. In recent years, studies from several groups have challenged the traditional dogma and demonstrated that monoclonal antibodies can modify various aspects of mycobacterial infections. This review describes the experimental evidence supporting a role for antibodies in defense against mycobacterial infections and outlines future challenges to the field of antibody-mediated immunity against M. tuberculosis, with particular emphasis on the implications of these findings for a novel vaccine strategy.

Latent tuberculosis: mechanisms of host and bacillus that contribute to persistent infection

Most people infected with Mycobacterium tuberculosis contain the initial infection and develop latent tuberculosis. This state is characterised by evidence of an immune response against the bacterium (a positive tuberculin skin test) but no signs of active infection. It can be maintained for the lifetime of the infected person. However, reactivation of latent infection occurs in about 10% of infected individuals, leading to active and contagious tuberculosis. An estimated 2 billion people worldwide are infected with M tuberculosis--an enormous reservoir of potential tuberculosis cases. The establishment and reactivation of latent infection depend on several factors, related to both host and bacterium. Elucidation of the host immune mechanisms that control the initial infection and prevent reactivation has begun. The bacillus is well adapted to the human host and has a range of evasion mechanisms that contribute to its ability to avoid elimination by the immune system and establish a persistent infection. We discuss here current understanding of both host and bacterial factors that contribute to latent and reactivation tuberculosis.

Host innate defenses in the lung: the role of cytokines

PURPOSE OF REVIEW

The lung has a unique relationship with the environment. Through evolution the lung has developed strategies to defend itself from microbial invasion. As we encounter increasing multidrug-resistant microorganisms, we need to further our knowledge of innate defense systems in order to design novel strategies to deal with these microbes without inducing over-exuberant inflammation and lung injury.

RECENT FINDINGS

The development of lung innate immunity requires microbial molecular pattern recognition by the recently described Toll like receptors, the release of early response cytokines that further activate the 'master switch', nuclear factor-kappaB, leading to amplified host defense to invading microbes. A balance of Type 1 and Type 2 cytokines modulates the intensity of innate immunity. Cytokines/chemokines orchestrate the polarization and transition of innate to adaptive immunity.

SUMMARY

The elucidation of the pathways involved in innate immunity and factors controlling the transition to adaptive immunity will improve our understanding of the host response to infection and improve our ability to design new therapies for the treatment of infectious disease.

Mast cell activation by Mycobacterium tuberculosis: mediator release and role of CD48

Mast cells (MC) are abundant in the lung and other peripheral tissue, where they participate in inflammatory processes against bacterial infections. Like other effector cells of the innate immune system, MC interact directly with a wide variety of infectious agents. This interaction results in MC activation and inflammatory mediator release. We demonstrated that MC interact with Mycobacterium tuberculosis, triggering the release of several prestored reagents, such as histamine and beta-hexosaminidase, and de novo synthesized cytokines, such as TNF-alpha and IL-6. A number of M. tuberculosis Ags, ESAT-6, MTSA-10, and MPT-63, have been implicated in MC activation and mediator release. A MC plasmalemmal protein, CD48, was implicated in interactions with mycobacteria because CD48 appeared to aggregate in the MC membrane at sites of bacterial binding and because Abs to CD48 inhibited the MC histamine response to mycobacteria. Cumulatively, these findings suggest that MC, even in the absence of opsonins, can directly recognize M. tuberculosis and its Ags and have the potential to play an active role in mediating the host's innate response to M. tuberculosis infection.

Anti-tumour necrosis factor agents and tuberculosis risk: mechanisms of action and clinical management

Cases of active tuberculosis have been reported worldwide with the use of therapeutic agents that inhibit tumour necrosis factor (TNF) alpha. TNFalpha has a central role in mycobacterial infection and disease. Accordingly, progression of recently acquired tuberculosis infection or reactivation of remotely acquired infection should be expected with the use of anti-TNF agents. The available in-vitro and epidemiological evidence for the two currently approved agents, infliximab and etanercept, shows that the risk of development of active tuberculosis is greater with infliximab. Tuberculin skin testing (TST) should be undertaken before any significant immunosuppressive therapy including these agents, though the possibility of false-negative reactions in immunocompromised populations must be borne in mind. A positive TST should be followed by medical assessment and chest radiography, as well as by other tests judged appropriate by the physician to identify active disease. Active tuberculosis must be treated appropriately before initiation of treatment with an anti-TNF agent. Treatment of latent tuberculosis can be considered on an individual basis for TST-negative patients receiving anti-TNF agents when significant risk factors for infection are present.

CD8+ T cells accumulate in the lungs of Mycobacterium tuberculosis-infected Kb-/-Db-/- mice, but provide minimal protection

Recent studies have shown that MHC class I molecules play an important role in the protective immune response to Mycobacterium tuberculosis infection. Here we showed that mice deficient in MHC class Ia, but possessing MHC class Ib (K(b-/-)D(b-/-) mice), were more susceptible to aerosol infection with M. tuberculosis than control mice, but less susceptible than mice that lack both MHC class Ia and Ib (beta(2)m(-/-) mice). The susceptibility of K(b-/-)D(b-/-) mice cannot be explained by the failure of CD8(+) T cells (presumably MHC class Ib-restricted) to respond to the infection. Although CD8(+) T cells were a relatively small population in uninfected K(b-/-)D(b-/-) mice, most already expressed an activated phenotype. During infection, a large percentage of these cells further changed their cell surface phenotype, accumulated in the lungs at the site of infection, and were capable of rapidly producing IFN-gamma following TCR stimulation. Histopathologic analysis showed widespread inflammation in the lungs of K(b-/-)D(b-/-) mice, with a paucity of lymphocytic aggregates within poorly organized areas of granulomatous inflammation. A similar pattern of granuloma formation has previously been observed in other types of MHC class I-deficient mice, but not CD8alpha(-/-) mice. Thus, neither the presence of MHC class Ib molecules themselves, nor the activity of a population of nonclassical CD8(+) effector cells, fully restored the deficit caused by the absence of MHC class Ia molecules, suggesting a unique role for MHC class Ia molecules in protective immunity against M. tuberculosis.

Deletion of RD1 from Mycobacterium tuberculosis mimics bacille Calmette-Guérin attenuation

The tuberculosis (TB) vaccine bacille Calmette-Guérin (BCG) is a live attenuated organism, but the mutation responsible for its attenuation has never been defined. Recent genetic studies identified a single DNA region of difference, RD1, which is absent in all BCG strains and present in all Mycobacterium tuberculosis (MTB) strains. The 9 open-reading frames predicted within this 9.5-kb region are of unknown function, although they include the TB-specific immunodominant antigens ESAT-6 and CFP-10. In this study, RD1 was deleted from MTB strain H37Rv, and virulence of H37Rv:DeltaRD1 was assessed after infections of the human macrophage-like cell line THP-1, human peripheral blood monocyte-derived macrophages, and C57BL/6 mice. In each of these systems, the H37Rv:DeltaRD1 strain was strikingly less virulent than MTB and was very similar to BCG controls. Therefore, it was concluded that genes within or controlled by RD1 are essential for MTB virulence and that loss of RD1 was important in BCG attenuation.

Florid pulmonary inflammatory responses in mice vaccinated with Antigen-85 pulsed dendritic cells and challenged by aerosol with Mycobacterium tuberculosis

Mice immunized by the intranasal route with dendritic cells harvested from the lungs and then pulsed with Ag85 (LDC-Ag85) were able to prime naive CD4(+) T cells in vivo. As a result splenic CD4(+) T cells from these immunized mice were able to produce IFNgamma following culture with Mycobacterium tuberculosis-infected antigen presenting cells. Hematoxylin and eosin stained lung sections from LDC-Ag85 immunized mice after they had been exposed to aerosol challenge with M. tuberculosis showed a florid infiltration of macrophages and lymphocytes into granulomas and parenchymal tissues when compared to lung sections from control groups implanted with dendritic cells pulsed with ovalbumin. In addition, using immunohistochemistry, these tissues appeared to have more CD4(+) and CD8(+) cells than the control groups. This was confirmed by flow cytometric analysis which showed that lung cell digests contained increased numbers of CD4 and CD8 interferongamma secreting cells. Despite this increase however, no evidence was seen that indicated that the LDC-Ag85 immunized mice were more resistant to M. tuberculosis infection than mice immunized with LDC pulsed with an irrelevant protein. Instead, the potent inflammatory response in the LDC-Ag85 resulted in serious consolidation of the lung tissue.