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

Biomarkers of obesity and subsequent cardiovascular events

Obesity is a major risk factor for cardiovascular diseases, but the mechanisms for increased cardiovascular risk in obesity are still unclear. Inflammation and increased oxidative stress are two potential mechanisms proposed to play a major role in the morbidity associated with obesity. Studies that investigate these mechanisms rely on biomarkers, but validated biomarkers for obesity-related cardiovascular outcomes are lacking. By finding optimal biomarkers, diagnostic criteria for cardiovascular diseases can be refined in the obese beyond "traditional" risk factors to identify early pathologic processes. The objective of this review is to identify potential early biomarkers resulting from obesity and associated with cardiovascular disease. Studies were initially identified through the search engine PubMed by using the keywords "obesity" and "biomarker." Subsequently, combinations of the keywords "obesity," "biomarker," "cardiovascular risk," "adipose tissue," "adipokine," "adipocytokine," and "oxidative stress" were used. The SOURCE database and Online Mendelian Inheritance in Man (OMIM) were used to obtain more information on the biomarkers. Results of the searches yielded a large number of potential biomarkers that occur in obesity and which either correlate with traditional cardiovascular risk factors or predict subsequent cardiovascular events. Several biomarkers are promising regarding their biologic properties, but they require further validation in humans.

T cell-derived TNF down-regulates acute airway response to endotoxin

Acute and chronic airway inflammations caused by environmental agents including endotoxin represent an increasing health problem. Local TNF production may contribute to lung dysfunction and inflammation, although pulmonary neutrophil recruitment occurs in the absence of TNF. First, we demonstrate that membrane-bound TNF is sufficient to mediate the inflammatory responses to lipopolysaccharide (LPS). Secondly, using cell type-specific TNF-deficient mice we show that TNF derived from either macrophage/neutrophil (M/N) or T lymphocytes have differential effects on LPS-induced respiratory dysfunction (enhanced respiratory pause, Penh) and pulmonary neutrophil recruitment. While Penh, vascular leak, neutrophil recruitment, TNF, and thymus- and activation-regulated chemokine/CCL17 (TARC) expression in the lung were reduced in M/N-deficient mice, T cell-specific TNF-deficient mice displayed augmented Penh, vascular leak, neutrophil influx, increased CD11c+ cells and expression of TNF, TARC and murine CXC chemokines KC/CXCL1 in the lung. In conclusion, inactivation of TNF in either M/N or T cells has differential effects on LPS-induced lung disease, suggesting that selective deletion of TNF in T cells may aggravate airway pathology.

Indirect regulation of CD4 T-cell responses by tumor necrosis factor receptors in an acute viral infection

Despite the well-recognized importance of CD4 T-cell help in the induction of antibody production and cytotoxic-T-lymphocyte responses, the regulation of CD4 T-cell responses is not well understood. Using mice deficient for TNF receptor I (TNFR I) and/or TNFR II, we show that TNFR I and TNFR II play redundant roles in down regulating the expansion of CD4 T cells during an acute infection of mice with lymphocytic choriomeningitis virus (LCMV). Adoptive transfer experiments using T-cell-receptor transgenic CD4 T cells and studies with mixed bone marrow chimeras indicated that indirect effects and not direct effects on T cells mediated the suppressive function of TNF on CD4 T-cell expansion during the primary response. Further studies to characterize the indirect effects of TNF suggested a role for TNFRs in LCMV-induced deletion of CD11c(hi) dendritic cells in the spleen, which might be a mechanism to limit the duration of antigenic stimulation and CD4 T-cell expansion. Consequent to enhanced primary expansion, there was a substantial increase in the number of LCMV-specific memory CD4 T cells in the spleens of mice deficient for both TNFR I and TNFR II. In summary, our findings suggest that TNFRs down regulate CD4 T-cell responses during an acute LCMV infection by a non-T-cell autonomous mechanism.

Tumor necrosis factor is critical to control tuberculosis infection

Tumor necrosis factor (TNF) is critical and non-redundant to control Mycobacterium tuberculosis infection and cannot be replaced by other proinflammatory cytokines. Overproduction of TNF may cause immunopathology, while TNF neutralization reactivates latent and chronic, controlled infection, which is relevant for the use of neutralizing TNF therapies in patients with rheumatoid arthritis.

Lactoferrin modulation of IL-12 and IL-10 response from activated murine leukocytes

Lactoferrin possesses a wide range of immunomodulatory activities, including promotion of the delayed type hypersensitivity response (DTH) towards BCG (Bacillus Calmette Guerin) antigens. Addition of Lactoferrin as an adjuvant to the BCG vaccine was previously demonstrated to augment protection against subsequent mycobacterial challenge, with concomitant development of a strong T cell helper type 1 (TH1) immunity. Because generation of TH1 immunity is in large part dependent on the balance of monocytic pro- and anti-inflammatory cytokines, the effect of Lactoferrin on leukocytes was investigated. Lactoferrin enhanced proinflammatory responses in a dose-dependant manner from splenocyte and adherent (F4/80+) splenocyte populations, bone marrow derived monocytes (BMM), and J774A.1 cultured cells. In all scenarios tested, Lactoferrin induced a strong increase in the ratio of IL-12:IL-10 production from LPS stimulated cells. Examination of Lactoferrin effects on BCG infected J774A.1 cells and on BMM revealed similar immunomodulatory effects, with particularly strong increase in IL-12 production. Furthermore, immunization of mice with BCG admixed with Lactoferrin led to increased generation of CD4+ cells expressing IFN-gamma upon restimulation with BCG antigens. These results provide molecular evidence to support the role of Lactoferrin as an adjuvant candidate to augment development of DTH response to vaccine antigens.

Mycobacterium bovis BCG vaccination modulates TNF-α production after pulmonary challenge with virulent Mycobacterium tuberculosis in guinea pigs

Tumor necrosis factor-alpha (TNF-alpha) plays critical and opposing roles in the pathogenesis of tuberculosis (TB). We examined the effects of Mycobacterium bovis BCG vaccination on TNF-alpha production in three distinct guinea pig leukocyte populations before and after pulmonary infection with M. tuberculosis H37Rv. Following BCG vaccination alone, and following challenge, bronchoalveolar lavage cells (BALC), resident peritoneal cells (PC), and splenocytes (SPC) were stimulated with purified protein derivative (PPD). Before virulent challenge, BCG vaccination clearly enhanced the ability of BALC, PC and SPC to produce TNF-alpha in response to PPD stimulation ex vivo. Following challenge, the TNF-alpha production of all three leukocyte populations from BCG-vaccinated animals remained relatively constant at pre-challenged levels. In sharp contrast, 5 weeks post-challenge, all three leukocyte populations from unvaccinated animals produced very high amounts of TNF-alpha in response to PPD. Three weeks post-challenge, SPC from one of the unvaccinated animals produced higher levels of TNF-alpha but the others produced lower levels of TNF-alpha than BCG-vaccinated animals. As expected, BCG vaccination reduced the levels of virulent mycobacteria in both the lungs and spleens. Thus, BCG vaccination allows guinea pigs to modulate TNF-alpha levels in conjunction with a reduction in bacillary loads in their tissues.

Gamma interferon responses of CD4 and CD8 T-cell subsets are quantitatively different and independent of each other during pulmonary Mycobacterium bovis BCG infection

Gamma interferon (IFN-gamma) is a key cytokine in host defense against intracellular mycobacterial infection. It has been believed that both CD4 and CD8 T cells are the primary sources of IFN-gamma. However, the relative contributions of CD4 and CD8 T-cell subsets to IFN-gamma production and the relationship between CD4 and CD8 T-cell activation have not been examined. By using a model of pulmonary mycobacterial infection and various immunodetection assays, we found that CD4 T cells mounted a much stronger IFN-gamma response than CD8 T cells at various times after mycobacterial infection, and this pronounced IFN-gamma production by CD4 T cells was attributed to both greater numbers of antigen-specific CD4 T cells and a greater IFN-gamma secretion capacity of these cells. By using major histocompatibility complex class II-deficient or CD4-deficient mice, we found that the lack of CD4 T cells did not negatively affect primary or secondary CD8 T-cell IFN-gamma responses. The CD8 T cells activated in the absence of CD4 T cells were capable of immune protection against secondary mycobacterial challenge. Our results suggest that, whereas both CD4 and CD8 T cells are capable of IFN-gamma production, the former represent a much greater cellular source of IFN-gamma. Moreover, during mycobacterial infection, CD8 T-cell IFN-gamma responses and activation are independent of CD4 T-cell activation.

Efficient Adsorption of Tumor Necrosis Factor with an in vitro Set-Up of the Microspheres-Based Detoxification System

BACKGROUND

The Microsperes-Based Detoxification System (MDS) represents a flexible therapeutic option for various diseases, depending on the specificity of the adsorbents applied. A potential application of the MDS is the supportive therapy of sepsis.

METHODS

Microadsorbents for tumor necrosis factor (TNF) were prepared by immobilization of anti-TNF antibodies on cellulose (1-10 microm) and applied in an experimental set-up using a pool of human plasma (1 liter) spiked with TNF (800 pg/ml) and its soluble receptors (1,000 pg/ml each). Removal of TNF was compared using a plasma filter and the albumin-permeable filter Albuflow.

RESULTS

Addition of 4 (2) g of adsorbent to the filtrate circuit reduced TNF concentrations in the pool by 80% (64%). Removal rates did not differ significantly for the different filters. TNF adsorption was not influenced by the presence of excess TNF receptors.

CONCLUSIONS

Concentrations of mediators can be efficiently modulated with the MDS using small quantities of specific adsorbents.

Impact of Biologic Agents on Infectious Diseases

Until recently, inflammatory diseases, collagen vascular diseases, inflammatory bowel diseases, and multiple sclerosis were met with a limited offering for treatment. The introduction of biologic agents has revolutionized the approach to these diseases, offering many patients freedom from disease activity staving off resultant destruction to organs and joints with marked improvement in quality of life and disability. This article focuses on the development of serious infections associated with the use of biologic agents. Presented is a synthesis of case series, reports, and systematic reviews to elucidate implicated pathogens and clinical presentations in patients being treated with biologic agents and to form a cursory backbone for prevention and treatment strategies to which clinicians prescribing these agents or encountering patients already on these agents can readily refer. Maintenance of a high index of suspicion is imperative for the prevention and appropriate treatment of serious life-threatening infections in these patients.

Indoleamine 2,3-dioxygenase-expressing dendritic cells form suppurative granulomas following Listeria monocytogenes infection

Control of pathogens by formation of abscesses and granulomas is a major strategy of the innate immune system, especially when effector mechanisms of adaptive immunity are insufficient. We show in human listeriosis that DCs expressing indoleamine 2,3-dioxygenase (IDO), together with macrophages, are major cellular components of suppurative granulomas in vivo. Induction of IDO by DCs is a cell-autonomous response to Listeria monocytogenes infection and was also observed in other granulomatous infections with intracellular bacteria, such as Bartonella henselae. Reporting on our use of the clinically applied anti-TNF-alpha antibody infliximab, we further demonstrate in vitro that IDO induction is TNF-alpha dependent. Repression of IDO therefore might result in exacerbation of granulomatous diseases observed during anti-TNF-alpha therapy. These findings place IDO(+) DCs not only at the intersection of innate and adaptive immunity but also at the forefront of bacterial containment in granulomatous infections.

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.

Role of tumor necrosis factor alpha in development of immunity against Cryptosporidium parvum infection

Tumor necrosis factor (TNF-alpha) significantly reduced Cryptosporidium parvum development in a murine enterocyte cell line, and a key mechanism of action appeared to be inhibition of parasite invasion. However, TNF-alpha-deficient mice controlled infection as effectively as wild-type mice. This suggests that TNF-alpha might have only a redundant role for establishing immunity against C. parvum.

Cytokine expression profiles of bovine lymph nodes: effects of Mycobacterium bovis infection and bacille Calmette-Guérin vaccination

Cytokine expression in lymph nodes from cattle inoculated intranasally with Mycobacterium bovis was compared to that of non-infected animals using real-time polymerase chain reaction. The effect of M. bovis infection, 4 months post-challenge, was to suppress the expression of anti-inflammatory cytokines interleukin (IL)-4 and IL-10 as well as the pro-inflammatory cytokines tumour necrosis factor (TNF) and IL-6. Expression of interferon (IFN)-gamma and IL-12 was maintained. Animals vaccinated with bacille Calmette-Guérin responded differently to challenge with M. bovis. In particular, no decrease in expression of IL-4 or IL-6 was observed following challenge of vaccinated animals and decreased IFN-gamma was detected. Also, vaccinated animals had higher levels of IL-4 and IL-10 transcripts compared to unvaccinated animals following challenge. These changes in cytokine expression levels led to a significant shift in the IFN-gamma/IL-4 or IFN-gamma/IL-10 ratio within the lymph node following challenge. Challenged animals generally showed a strong Th1 bias that was not seen in animals vaccinated prior to challenge. An inverse correlation between the level of pathology and bacterial load within the lymph node and the expression of IL-4, IL-10 and TNF was also observed. These results suggest that in the lymph nodes of cattle with established tuberculosis and a persisting bacterial infection, maintenance of the pro-inflammatory response in combination with a suppressed anti-inflammatory response may control the infection but contribute to host-induced tissue damage. Vaccination, which reduces the bacterial load and consequently the IFN-gamma response, may result in less suppression of anti-inflammatory cytokines.

Differential requirements for soluble and transmembrane tumor necrosis factor in the immunological control of primary and secondary Listeria monocytogenes infection

The relative contributions of transmembrane tumor necrosis factor (memTNF) and soluble tumor necrosis factor (solTNF) in innate and adaptive immunity are poorly defined. We examined the capacities of wild-type (WT) mice, TNF-/- mice, and memTNF mice, which express only transmembrane TNF, to control primary and secondary Listeria monocytogenes infections. Soluble TNF was not required for induction or maintenance of protective immunity against a low-dose (200-CFU) Listeria infection. In contrast to TNF-/- mice, both WT and memTNF mice cleared the bacilli within 10 days and were fully protected against rechallenge with a lethal infective dose. Furthermore, T cells transferred from immune mice, but not from naïve, WT, and memTNF mice, protected TNF-/- recipients against an otherwise lethal infection. By contrast, infection with a higher dose of Listeria (2,000 CFU) clearly demonstrated that solTNF is required to coordinate an optimal protective inflammatory response. memTNF mice were more susceptible to a high-dose infection, and they exhibited delayed bacterial clearance, increased inflammation, and necrosis in the liver that resulted in 55% mortality. The dysregulated inflammation was accompanied by prolonged elevated expression of mRNAs for several chemokines as well as the macrophage effector molecules inducible nitric oxide synthase and LRG-47 in the livers of memTNF mice but not in the livers of WT mice. These data demonstrated that memTNF is sufficient for establishing protective immunity against a primary low-dose Listeria infection but that solTNF is required for optimal control of cellular inflammation and resistance to a primary high-dose infection. By contrast, memTNF alone is sufficient for resolution of a secondary, high-dose infection and for the transfer of protective immunity with memory T cells.

Polymorphisms in the TNF-alpha promoter and variability in the granulomatous response in patients with Crohn's disease

Granulomas may be found in 30-70% of patients with Crohn's disease (CD). The etiology of granuloma formation in CD is presently unknown. Elevated levels of TNF-alpha are found within granuloma tissue, and are required to maintain granuloma formation in animal models. TNF-alpha production has been shown to influenced by TNF-alpha promoter polymorphisms. We hypothesized that heterogeneity for granulomas in CD might be influenced by the TNF-alpha promoter genotype. Patients with confirmed CD that had undergone full colonoscopy with multiple biopsies and/or surgical resection, served as the study group. One hundred healthy individuals served as a control population for genotyping. Patients and controls underwent genotyping for four TNF-alpha polymorphisms: 238G/A, 308 G/A,857 C/T, and 863 C/A. Inclusion and exclusion criteria were met in 155 patients (1-68 y). Polymorphisms in the TNF promoter were found in 16.6% (238G/A), 14.5% (308 G/A), 36.6% (857 C/T) and 30.7% (863G/A). No significant association was found for any of the individual polymorphisms with presence or absence of granulomas. In conclusion, we did not find an association between individual polymorphisms in the TNF-alpha promoter and presence of granulomas in CD. The reason for heterogeneity in granuloma formation in patients with CD remains elusive.

Aggravated infection in mice co-administered with Mycobacterium tuberculosis and the 27-kDa lipoprotein

We have previously reported that mice immunized with the mycobacterial 27-kDa lipoprotein were more susceptible to Mycobacterium tuberculosis (Mtb) challenge. We also showed that 27-kDa lipoprotein abrogated the protection afforded by the BCG vaccine when administrated together, suggesting that the 27-kDa lipoprotein may modulate the course of experimental mycobacterial infection. In this study, we address the role of the 27-kDa lipoprotein in modulating the immune response to mycobacteria. Our results show that co-administration of BALB/c mice with Mtb and the 27-kDa lipoprotein (Mtb+27kDa), but not its non-acylated form, increases the susceptibility of mice to Mtb infection. Significantly lower DTH reaction and splenocyte proliferation to PPD stimulation were also observed in Mtb+27kDa-infected mice compared to Mtb-infected mice. Furthermore, during infection, splenocytes and purified T cells lost their ability to proliferate in response to concanavalin A stimulation more rapidly in the Mtb+27kDa-infected mice, which was accompanied by high IFN-gamma and NO production, but low TNF-alpha secretion levels. Addition of L-NMMA, anti-IFN-gamma and anti-TNF-alpha antibodies restored in vitro proliferative responses of T cells from Mtb+27kDa-infected mice. Short-term L-NMMA treatment of Mtb+27kDa-infected mice prevented the 27-kDa-mediated immunosuppression and increase in susceptibility to Mtb. Altogether, these data suggest that the 27-kDa lipoprotein plays a role in Mtb infection by inducing increased suppression of the immune response due to elevated NO production.

Membrane tumor necrosis factor confers partial protection to Listeria infection

Tumor necrosis factor (TNF) plays a critical role in the host response to the intracellular pathogen Listeria monocytogenes (LM). TNF exists in soluble and membrane-bound forms and exhibits both unique and overlapping activities. We examined the role of membrane TNF in the absence of secreted TNF for host resistance in knockin mice in which the endogenous TNF was replaced by a regulated, noncleavable allele (mem-TNF). Macrophages expressing mem-TNF produced nitric oxide and displayed normal bactericidal activity. Although mice completely deficient in TNF (TNF(-/-)) succumbed to LM infection within 4 days, mem-TNF mice controlled LM infection at a low dose (10(4) CFU) but succumbed at a higher dose of infection (10(5) CFU). In contrast to complete TNF deficiency, mem-TNF mice developed confined microabscesses that expressed inducible nitric oxide synthase. The transfer of lymphocytes from immunized mem-TNF, but not TNF(-/-), mice protected TNF(-/-) mice from fatal infection. Taken together the data suggest that in the absence of soluble TNF, the presence of membrane-expressed TNF on phagocytes and lymphocytes partially restores host defense to LM infection.

Tumour necrosis factor-alpha as a tumour promoter

It is becoming more evident that many aspects of tumour promotion arise from persistent and unresolving inflammation. One of the key molecules mediating the inflammatory processes in tumour promotion is the cytokine, tumour necrosis factor-alpha (TNF-alpha). Clinically, elevated serum concentrations and increased expression of TNF-alpha are present in various pre-neoplastic and malignant diseases, compared with serum and tissue from healthy individuals. Although over the last few decades high-dose administration of TNF-alpha has been used as a cytotoxic agent, recent pre-clinical cancer models have provided critical evidence to support the link between chronic, low level TNF-alpha exposure and the acquisition of pro-malignant phenotype (i.e., increased growth, invasion and metastasis). Furthermore, sophisticated cellular systems are being utilised to dissect the crucial role TNF-alpha plays in the communication of stromal/inflammatory cells and tumour cells. Understanding the intricate roles of TNF-alpha in the process of tumour promotion will assist in the development of novel cancer therapeutics.

Use of cytokines in infection

Infectious disease remains an ever-growing health concern worldwide due to increasing antibiotic-resistant microbial strains, immune-compromised populations, international traffic and globalisation, and bioterrorism. There exists an urgent need to develop novel prophylactic and therapeutic strategies. In addition to classic antibiotic therapeutics, immune-modulatory molecules such as cytokines or their inhibitors represent a promising form of antimicrobial therapeutics or immune adjuvant used for the purpose of vaccination. These molecules, in the form of either recombinant protein or transgene, exert their antimicrobial effect by enhancing infectious agent-specific immune activation or memory development, or by dampening undesired inflammatory and immune responses resulting from infection and host defence mechanisms. In the last two decades, a number of cytokine therapy-based experimental and clinical trials have been conducted, and some of these efforts have led to the routine clinical use of cytokines. For instance, although IFNs have been used to treat hepatitis C with great success, many other cytokines are yet to be fully evaluated for their antimicrobial potential. This review discusses the biology and therapeutic potential of selected immune modulatory cytokines and their inhibitors, including granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, IFN-gamma, IL-12 and TNF.

Animal models of cavitation in pulmonary tuberculosis

Transmission of tuberculosis occurs with the highest frequency from patients with extensive, cavitary, pulmonary disease and positive sputum smear microscopy. In animal models of tuberculosis, the development of caseous necrosis is an important prerequisite for the formation of cavities although the immunological triggers for liquefaction are unknown. We review the relative merits and the information gleaned from the available animal models of pulmonary cavitation. Understanding the host-pathogen interaction important to the formation of cavities may lead to new strategies to prevent cavitation and thereby, block transmission.

Temporal cytokine gene expression patterns in subjects with trachoma identify distinct conjunctival responses associated with infection

Ocular chlamydial disease is clinically diagnosed by the appearance of characteristic inflammatory changes and development of lymphoid follicles in the conjunctiva. Nucleic acid amplification tests and relatively non-invasive methods of sampling the conjunctival surface can be used to quantify the expression of chlamydial and host genes. Using quantitative real-time polymerase chain reaction to detect the presence of Chlamydia trachomatis (CT) 16S rRNA and human interleukin (IL)-1beta, IL-10, IL-12p40, interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha transcripts we examined the immune response at the conjunctival surface in a cohort of children living in a trachoma-endemic village in The Gambia. Elevated cytokine transcript levels were associated with the presence of CT 16S rRNA. Subclinical infection (CT infection without clinical signs of disease) elicited an immune response that is proinflammatory in nature, with elevations in the transcription of IL-1beta, IFN-gamma and IL-12p40. Clinically apparent infections were associated with the elevation of mRNA for the multi-functional cytokine TNF-alpha (fibrotic, type 1 inflammatory and regulatory) and the counter regulatory cytokine, IL-10, in addition to the other proinflammatory cytokines. A positive correlation between IFN-gamma transcript levels and the amount of CT 16S rRNA expressed in conjunctiva was found.

Membrane TNF confers protection to acute mycobacterial infection

Background

Tumour necrosis factor (TNF) is crucial for the control of mycobacterial infection as TNF deficient (KO) die rapidly of uncontrolled infection with necrotic pneumonia. Here we investigated the role of membrane TNF for host resistance in knock-in mice with a non-cleavable and regulated allele (mem-TNF).

Methods

C57BL/6, TNF KO and mem-TNF mice were infected with M. tuberculosis H37Rv (Mtb at 100 CFU by intranasal administration) and the survival, bacterial load, lung pathology and immunological parameters were investigated. Bone marrow and lymphocytes transfers were used to test the role of membrane TNF to confer resistance to TNF KO mice.

Results

While TNF-KO mice succumbed to infection within 4–5 weeks, mem-TNF mice recruited normally T cells and macrophages, developed mature granuloma in the lung and controlled acute Mtb infection. However, during the chronic phase of infection mem-TNF mice succumbed to disseminated infection with necrotic pneumonia at about 150 days. Reconstitution of irradiated TNF-KO mice with mem-TNF derived bone marrow cells, but not with lymphocytes, conferred host resistance to Mtb infection in TNF-KO mice.

Conclusion

Membrane expressed TNF is sufficient to allow cell-cell signalling and control of acute Mtb infection. Bone marrow cells, but not lymphocytes from mem-TNF mice confer resistance to infection in TNF-KO mice. Long-term infection control with chronic inflammation likely disrupting TNF mediated cell-cell signalling, additionally requires soluble TNF.

Differential effects of total and partial neutralization of tumor necrosis factor on cell-mediated immunity to Mycobacterium bovis BCG infection

The effects of total and partial inhibition of tumor necrosis factor (TNF) on sensitivity to Mycobacterium bovis BCG infection were investigated by using transgenic mice in which hepatocytes produced different amounts of human soluble TNF receptor 1 (sTNFR1) fused to the Fc fragment of human immunoglobulin G3 that could be detected in the serum. Transgenic mice expressing high serum levels of sTNFR1, neutralizing all circulating TNF, failed to develop differentiated granulomas and bactericidal mechanisms, and they succumbed to BCG infection. sTNFR1 transgenic mice did not activate BCG-induced Th1-type cytokines early in infection, but uncontrolled cytokine release was found late in infection. In this work we also evaluated the effect of partial inhibition of TNF on resistance to BCG infection. Transgenic mice expressing low levels of sTNFR1 were protected against BCG infection, and they developed increased bactericidal mechanisms, such as enhanced inducible nitric oxide synthase activity, increased macrophage activation, and showed higher numbers of liver granulomas early in infection compared to their negative littermates. Our data suggest that while total inhibition of TNF prevented BCG-induced cell-mediated immune responses, partial inhibition of TNF could contribute to macrophage activation, induction of bactericidal mechanisms, and granuloma formation in the early phase of BCG infection.

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.

Increased specific T cell cytokine responses in patients with active pulmonary tuberculosis from Central Africa

An understanding of T cell responses that are crucial for control of Mycobacterium tuberculosis (MTB) has major implications for the development of immune-based interventions. We studied the frequency of purified protein derivative (PPD)-specific CD3) cells expressing interleukin-2 (IL)-2, gamma interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha and IL-10 in HIV-negative pulmonary tuberculosis patients (TB, n=30) as well as in healthy individuals (controls, n=21) from Central Africa. Increased frequencies of PPD-stimulated CD3+ cells expressing IL-2, IFN-gamma, and TNF-alpha in TB were seen when compared with frequencies of controls. The presence of type 1 cytokine biased responses in TB patients was supported by a shift in the distribution pattern of cytokine expression from exclusively IL-2 or TNF-alpha expression seen in controls towards an increased frequency of IFN-gamma/IL-2 or IFN-gamma/TNF-alpha co-expression in TB. Higher levels of PPD-induced IFN-gamma in the supernatants from TB patients than from controls were found, which correlated with its intracellular expression. PPD was a weak inducer of IL-10 in T cells and insufficient in promoting cytokine production in TCRgammadelta+CD3+ cells. Non-specific stimulation with PMA and ionomycin revealed increased frequencies of CD4+ cells expressing IFN-gamma in controls, while expression of IL-2, IL-4, IL-10, IL-13, and TNF-alpha was not different. Non-specific cytokine responses of TCRgammadelta+CD3+ cells were similar in all groups. Pulmonary TB in Central Africa is associated with enhanced expression and secretion of specifically induced cytokines that are frequently implicated in host defense against MTB.

Structure-modifying capacity of anti-tumour necrosis factor-alpha therapy in ankylosing spondylitis

Spondylarthropathies (SpA) present mainly with spondylitis, pauciarticular peripheral arthritis and enthesopathy. Ankylosing spondylitis (AS) is the prototype disease in this concept. Other entities include reactive arthritis, arthritis in patients with inflammatory bowel disease, some forms of psoriatic arthritis and undifferentiated SpA. NSAIDs are the classical cornerstone of medical therapy in patients with SpA. The effect of these drugs on disease progression, more specifically the ankylosis, is uncertain. Sulfasalazine can be combined with NSAIDs, particularly if peripheral arthritis symptoms persist. However, this combination therapy is not effective for the spondylitis symptoms. Indeed, AS is one of the rheumatic diseases for which no real disease-modifying antirheumatic treatment is available. Challenges in chronic autoimmune arthritis have changed dramatically, especially since biotechnological compounds became available. These compounds allow for a specific intervention in the immune cascade underlying the disease. Tumour necrosis factor (TNF)-alpha antagonists (monoclonal antibodies such as infliximab, or soluble receptors such as etanercept) are the first representative drugs in this category. Open-label studies have shown the efficacy of these new targeted drugs, which has been confirmed by controlled studies, at least in the short term. Improvements in several clinical parameters, function, quality of life, biological parameters, histopathological synovial characteristics and magnetic resonance imaging, have all been observed. As a result of these favourable results, anti-TNFalpha therapy has been approved for the treatment of AS and should be considered for patients with severe axial symptoms and elevated serological markers of inflammatory activity who have responded inadequately to conventional nonsteroidal therapy. There is evidence that this new therapeutic approach has a disease- and even structure-modifying effect in SpA. In this context, structure modification should not only be seen as inhibition of bone and cartilage destruction but more broadly as modulation of tissue histology. Some questions remain unanswered, such as the long-term efficacy and safety of anti-TNFalpha therapy, the extent of structural benefit and the cost effectiveness. However, despite these concerns, anti-TNFalpha therapy represents a major therapeutic advancement in the treatment of AS.

TNF-blocking agents and tuberculosis: new drugs illuminate an old topic

Newer TNF blockers (etanercept, infliximab and adalimumab) have contributed greatly to the control of chronic inflammatory disease. Many of the damaging inflammatory mechanisms that they inhibit are, however, important in maintaining tuberculosis in the latent phase (latent tuberculosis infection or LTBI). There is considerable evidence that links reactivation of LTBI to the use of anti-TNF monoclonal antibody (mAb) treatments, which appear to result in disruption of the granuloma that normally compartmentalizes but does not kill Mycobacterium tuberculosis during LTBI. This effect can be explained, in part, by directly neutralizing TNF, which plays a key role in tuberculosis immunity. To the clinician, dealing with LTBI in patients on these medications is an important issue. Prescribers should seek local expert help in this regard, as global LTBI treatment regimens differ. Nonetheless, screening for and treating LTBI will prevent reactivation in most patients. LTBI screening should include a careful history, tuberculin skin test and chest radiograph. Prophylactic treatment (e.g. isoniazid for 9 months) should be offered to patients with LTBI, in accordance with local advice. False-negative tuberculin skin test results can be expected in these patient groups. False-negative skin tests also mean that clinicians cannot be complacent about patients on TNF blockers who lack evidence of LTBI. On the contrary, because tuberculosis disease can be lethal, all treated patients should be advised to seek medical attention if symptoms suggestive of tuberculosis emerge. The indications for these successful agents are expanding, and efficient management of the LTBI issue should improve their safety profile.

Mycobacterium tuberculosis controls host innate immune activation through cyclopropane modification of a glycolipid effector molecule

Mycobacterium tuberculosis (Mtb) infection remains a global health crisis. Recent genetic evidence implicates specific cell envelope lipids in Mtb pathogenesis, but it is unclear whether these cell envelope compounds affect pathogenesis through a structural role in the cell wall or as pathogenesis effectors that interact directly with host cells. Here we show that cyclopropane modification of the Mtb cell envelope glycolipid trehalose dimycolate (TDM) is critical for Mtb growth during the first week of infection in mice. In addition, TDM modification by the cyclopropane synthase pcaA was both necessary and sufficient for proinflammatory activation of macrophages during early infection. Purified TDM isolated from a cyclopropane-deficient pcaA mutant was hypoinflammatory for macrophages and induced less severe granulomatous inflammation in mice, demonstrating that the fine structure of this glycolipid was critical to its proinflammatory activity. These results established the fine structure of lipids contained in the Mtb cell envelope as direct effectors of pathogenesis and identified temporal control of host immune activation through cyclopropane modification of TDM as a critical pathogenic strategy of Mtb.

Role of tumor necrosis factor receptors in regulating CD8 T-cell responses during acute lymphocytic choriomeningitis virus infection

The role of tumor necrosis factor (TNF) in regulating various phases of the antiviral T-cell response is incompletely understood. Additionally, despite strong evidence ascribing a role for TNF in protecting against T-cell-dependent autoimmunity, the underlying mechanisms are still obscure. To address these issues, we have investigated the role of tumor necrosis factor receptors (TNFRs) I (p55R) and II (p75R) in regulating CD8 T-cell responses to lymphocytic choriomeningitis virus (LCMV) with wild-type, p55R-deficient (p55(-/-)), p75R-deficient (p75(-/-)), and p55R- and p75R-deficient (DKO) mice. Loss of p55R increased the number of memory CD8 T cells to only one of the two immunodominant epitopes, and p75R deficiency had a minimal impact on the T-cell response to LCMV. Strikingly, deficiency of both p55R and p75R had a more dramatic effect on the LCMV-specific CD8 T-cell response; in the DKO mice, as a sequel to enhanced expansion and a reduction in contraction of CD8 T cells, there was a substantial increase in the number of memory CD8 T cells (specific to the two immunodominant epitopes). While the majority of LCMV-specific memory CD8 T cells in wild-type mice were CD62Lhi CCR7hi (central memory), a major proportion of memory CD8 T cells in DKO mice were CD62Llo CCR7hi. TNFR deficiency did not affect the proliferative renewal of memory CD8 T cells. Taken together, these data suggested that TNFRs p55R and p75R have overlapping roles in downregulating CD8 T-cell responses and establishment of immune homeostasis during an acute viral infection.

Granuloma necrosis during Mycobacterium avium infection does not require tumor necrosis factor

The infection of tumor necrosis factor (TNF)-deficient mice with low doses of the virulent Mycobacterium avium strain 25291 led to the appearance of necrotic granulomas at 93 days of infection, i.e., sooner than necrotic granulomas appeared in C57BL/6 animals. Additionally, TNF-deficient mice exhibited higher mycobacterial loads in the infected organs, had extremely exacerbated gamma interferon responses as evaluated in the sera of infected animals, and showed reduced survival. Thus, TNF is not required for granuloma necrosis.