Human tumor necrosis factor increases the resistance against Listeria infection in mice

Tumor necrosis factor (TNF) inhibitors for psoriatic arthritis

BACKGROUND

Psoriatic arthritis (PsA) is a chronic arthritis affecting people with psoriasis. If untreated, it may lead to disability. Recommended drugs are non-steroidal anti-inflammatory drugs (NSAIDs), corticosteroids, conventional synthetic disease-modifying anti-rheumatic drugs (csDMARDs), biologic DMARDs (bDMARDs), and targeted synthetic DMARDs (tsDMARDs). Tumour necrosis factor inhibitors (TNFi) are the first choice bDMARDs.

OBJECTIVES

To assess the benefits and harms of TNFi in adults with psoriatic arthritis.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, ClinicalTrials.gov and the World Health Organization trials portal up to 28 March 2024.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) in adults with PsA, comparing TNFi to placebo, physiotherapy, NSAIDs, corticosteroids, and cs/b/tsDMARDs. Major outcomes included clinical improvement, minimal disease activity, physical function, health-related quality of life, radiographic progression, serious adverse events, and withdrawals due to adverse events.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. The primary comparison was TNFi versus placebo. The primary time point was 12 weeks for clinical improvement; 24 weeks for minimal disease activity, function, quality of life, and radiographic progression; and the end of the trial period for serious adverse events and withdrawals due to adverse events.

MAIN RESULTS

We included 25 RCTs randomizing 7857 participants. Four studies compared TNFi to methotrexate and one to ustekinumab in DMARD-naïve participants. In csDMARD-inadequate responders, 11 studies compared TNFi to placebo; four studies compared TNFi to placebo and ixekizumab, bimekizumab, tofacitinib, or upadacitinib; and three studies compared TNFi to ixekizumab, secukinumab, and ustekinumab. Two studies compared different TNFi. We found no studies with b/tsDMARD-inadequate responders (b/tsDMARD-IR). No studies compared TNFi to NSAIDs, corticosteroids, or physiotherapy. Performance (32%), detection (56%) and reporting (80%) biases were at high or unclear risk across studies. Only one study had a low risk of bias in all domains. We limit reporting to the primary comparison, TNFi versus placebo. DMARD-naïve We found no studies comparing TNFi with placebo in DMARD-naïve participants. csDMARD-inadequate responders TNFi probably result in a large clinical improvement compared to placebo. At 12 weeks, 149/1926 (8%) participants in the placebo group showed a clinical improvement (ACR50) compared to 784/2141 (37%) participants in the TNFi group (risk ratio (RR) 5.63, 95% confidence interval (CI) 3.98 to 7.96; I2 = 65%; 14 studies, 4067 participants; moderate-certainty evidence). TNFi probably result in a higher proportion of participants in minimal disease activity. At 24 weeks, 95/1017 (9%) participants in the placebo group were in minimal disease activity compared to 428/1336 (32%) participants in the TNFi group (RR 3.76, 95% CI 2.39 to 5.92; I2 = 72%; 5 studies, 2353 participants; moderate-certainty evidence). At 24 weeks, TNFi may improve function compared to placebo. The mean change in function from baseline (assessed with the Health Assessment Questionnaire; score from 0 to 3, 0 = no disability; minimal clinically important difference (MCID) = 0.35) was -0.14 points with placebo and 0.33 points lower (0.41 lower to 0.25 lower) with TNFi (I2 = 72%; 8 studies, 2949 participants; low-certainty evidence). TNFi probably result in a clinically important improvement in health-related quality of life. The mean change in quality of life from baseline (assessed with the Short Form 36-item Mental Component Summary questionnaire; score from 0 to 100, 100 = best score; MCID = 1.7) was 2.4 points with placebo and 3.29 points higher (2.18 points higher to 4.40 points higher) with TNFi (I2 = 52%; 8 studies, 2928 participants; moderate-certainty evidence). TNFi probably slightly reduce radiographic progression. The mean change in radiographic progression (assessed with the Sharp/Van der Heijde-PsA score; scale from 0 to 528, 0 = no damage) was 0.25 points with placebo and 0.37 points lower with TNFi (0.48 lower to 0.25 lower) (I2 = 32%; 7 studies, 2478 participants; moderate-certainty evidence) at 24 weeks. We downgraded the evidence to moderate certainty for clinical improvement, minimal disease activity, quality of life, and radiographic progression due to risk of bias. For function, we downgraded the evidence to low certainty for risk of bias and imprecision. TNFi may result in little to no difference in serious adverse events, but may slightly increase withdrawals due to adverse events, compared to placebo. At the end of follow-up: 56/1826 participants (3%) given placebo and 69/1900 (4%) participants given TNFi experienced serious adverse events (RR 1.00, 95% CI 0.70 to 1.42; I2 = 0%; 13 studies, 3866 participants; low-certainty evidence); and 35/1926 (2%) participants given placebo and 65/2140 (3%) given TNFi withdrew due to adverse events (RR 1.53, 95% CI 1.01 to 2.33; I2 = 0%; 14 studies, 4066 participants; low-certainty evidence). We downgraded the evidence to low certainty for risk of bias and imprecision.

AUTHORS' CONCLUSIONS

In csDMARD-inadequate responders, moderate-certainty evidence showed that TNFi probably result in a large clinical improvement, lower disease activity, small decrease in radiographic progression, and better quality of life compared to placebo. Low-certainty evidence showed that TNFi may lead to a slight improvement in physical function compared to placebo. Low-certainty evidence suggested that TNFi may lead to a slight increase in withdrawals due to adverse events, whereas they may result in little to no difference in serious adverse events compared to placebo. No trials assessed TNFi compared to placebo in DMARD-naïve participants or in b/tsDMARD-IR.

Biomimetic Systems Involving Macrophages and Their Potential for Targeted Drug Delivery

The concept of targeted drug delivery can be described in terms of the drug systems' ability to mimic the biological objects' property to localize to target cells or tissues. For example, drug delivery systems based on red blood cells or mimicking some of their useful features, such as long circulation in stealth mode, have been known for decades. On the contrary, therapeutic strategies based on macrophages have gained very limited attention until recently. Here, we review two biomimetic strategies associated with macrophages that can be used to develop new therapeutic modalities: first, the mimicry of certain types of macrophages (i.e., the use of macrophages, including tumor-associated or macrophage-derived particles as a carrier for the targeted delivery of therapeutic agents); second, the mimicry of ligands, naturally absorbed by macrophages (i.e., the use of therapeutic agents specifically targeted at macrophages). We discuss the potential applications of biomimetic systems involving macrophages for new advancements in the treatment of infections, inflammatory diseases, and cancer.

Absence of TNF Leads to Alternative Activation in Peritoneal Macrophages in Experimental Listeria Monocytogenes Infection

Macrophages are crucial effectors of innate immunity against the pathogenic bacterium Listeria monocytogenes. The pro-inflammatory cytokine tumour necrosis factor-α (TNF) has been shown to be crucial for resistance to L. monocytogenes and mice deficient in TNF signalling succumb quickly after infection. However, the mechanisms underlying TNF-mediated defence against L. monocytogenes infection have not been completely elucidated. Here, we demonstrate that TNF concurrently functions to support a pro-inflammatory M1 phenotype while actively blocking macrophage polarization to the M2 phenotype. Compared to WT mice, peritoneal macrophages in TNF-deficient mice inoculated with L. monocytogenes respond with M2 polarization by upregulating Arg1. Consistently, TNF blockade in vitro resulted in M2 polarization in peritoneal macrophages during L. monocytogenes infection. Additionally, TNF promotes the transition from M2 to M1 polarization in peritoneal macrophages. Further investigation of peritoneal macrophage polarization suggested the NF-κB pathway is involved in the TNF-dependent M2 to M1 shift. Conversely, treatment of peritoneal macrophage with a PPARγ agonist blunted the expression of M1 genes induced by TNF and reduced NF-κB signalling pathway activation. Competing signalling mechanisms therefore play an essential role in the ability of peritoneal macrophage to resolve L. monocytogenes infections with TNF playing an essential role in driving M1 polarization.Abbreviations: LPM: large peritoneal macrophage; SPM: small peritoneal macrophage; LLO: listeriolysin O; iNOS: inducible nitric oxide synthase; DCs: dendritic cells.

Naringin rescued the TNF-α-induced inhibition of osteogenesis of bone marrow-derived mesenchymal stem cells by depressing the activation of NF-кB signaling pathway

Naringin exhibits antiinflammatory activity and is shown to induce bone formation. Yet the impact of naringin on inflammation-affected bone marrow-derived mesenchymal stem cell (BM-MSC), a promising tool for the regenerative treatment of bone injury, remained to be investigated. We first cultured and characterized the BM-MSCs in vitro and observe the effects of treatments of TNF-α, naringin, or the combination of both on osteogenic differentiation. TNF-α administered at the concentration of 20 ng/ml results in significant reductions in MSC's cell survival, alkaline phosphatase activity and expressions of two osteogenic genes, Runx2 and Osx. Simultaneous treatment of both TNF-α and naringin is able to rescue such reductions. Further mechanistic studies indicate that TNF-α treatment activates the NF-кB signaling pathway, evidenced by elevated p-IкBα level as well as the increased nuclear fraction of NF-кB subunit, p65. Finally, treatment with both TNF-α and naringin decreases expressions of p-IкBα and nuclear p65, and thus represses NF-кB pathway activated by sole TNF-α treatment. Our findings provide a molecular basis by which naringin restores the TNF-α-induced damage in MSCs and provide novel insights into the application of naringin in the MSC-based treatments for inflammation-induced bone injury.

Simvastatin enhances protection against Listeria monocytogenes infection in mice by counteracting Listeria-induced phagosomal escape

Statins are well-known cholesterol lowering drugs targeting HMG-CoA-reductase, reducing the risk of coronary disorders and hypercholesterolemia. Statins are also involved in immunomodulation, which might influence the outcome of bacterial infection. Hence, a possible effect of statin treatment on Listeriosis was explored in mice. Statin treatment prior to subsequent L. monocytogenes infection strikingly reduced bacterial burden in liver and spleen (up to 100-fold) and reduced histopathological lesions. Statin-treatment in infected macrophages resulted in increased IL-12p40 and TNF-α and up to 4-fold reduced bacterial burden within 6 hours post infection, demonstrating a direct effect of statins on limiting bacterial growth in macrophages. Bacterial uptake was normal investigated in microbeads and GFP-expressing Listeria experiments by confocal microscopy. However, intracellular membrane-bound cholesterol level was decreased, as analyzed by cholesterol-dependent filipin staining and cellular lipid extraction. Mevalonate supplementation restored statin-inhibited cholesterol biosynthesis and reverted bacterial growth in Listeria monocytogenes but not in listeriolysin O (LLO)-deficient Listeria. Together, these results suggest that statin pretreatment increases protection against L. monocytogenes infection by reducing membrane cholesterol in macrophages and thereby preventing effectivity of the cholesterol-dependent LLO-mediated phagosomal escape of bacteria.

OatA, a peptidoglycan O-acetyltransferase involved in Listeria monocytogenes immune escape, is critical for virulence

Microbial pathogens have evolved mechanisms to overcome immune responses and successfully infect their host. Here, we studied how Listeria monocytogenes evades immune detection by peptidoglycan (PGN) modification. By analyzing L. monocytogenes muropeptides, we detected O-acetylated muramic acid residues. We identified an O-acetyltransferase gene, oatA, in the L. monocytogenes genome sequence. Comparison of PGN from parental and isogenic oatA mutant strains showed that the O-acetyltransferase OatA O-acetylates Listeria PGN. We also found that PGN O-acetylation confers resistance to different types of antimicrobial compounds targeting bacterial cell wall such as lysozyme, β-lactam antibiotics, and bacteriocins and that O-acetylation is required for Listeria growth in macrophages. Moreover, oatA mutant virulence is drastically affected in mice following intravenous or oral inoculation. In addition, the oatA mutant induced early secretion of proinflammatory cytokines and chemokines in vivo. These results suggest an important role for OatA in limiting innate immune responses and promoting bacterial survival in the infected host.

Macrophage and dendritic cell phenotypic diversity in the context of biomaterials

Macrophages (Mϕ) and dendritic cells (DCs) are critical antigen presenting cells that play pivotal roles in host responses to biomaterial implants. Although Mϕs have been widely studied for their roles in the inflammatory responses against biomaterials, the roles that DCs play in the host responses toward implanted materials have only recently been explored. DCs are of significant research interest because of the emergence of a large number of combination products that cross-traditional medical device boundaries. These products combine biomaterials with biologics, including cells, nucleic acids, and/or proteins. The biomaterial component may evoke an inflammatory response, primarily mediated by neutrophils and Mϕs, whereas the biologic component may elicit an immunogenic immune response, initiated by DCs involving lymphocyte activation. Control of Mϕ phenotypic balance from proinflammatory M1 to reparative M2 is a goal of investigators to optimize the host response to biomaterials. Similarly, control of DC phenotype from proinflammatory to toleragenic is of interest in vaccine delivery and tissue engineering/transplantation situations, respectively. This review discusses the interconnection between innate and adaptive immunity, the comparative and contrasting phenotypes and roles of Mϕs and DCs in immunity, their responses to biomaterials and the strategies to modulate their phenotype for applications in tissue engineering and vaccine delivery. Furthermore, the collaboration between and unique roles of DCs and Mϕs needs to be addressed in future studies to gain a more complete picture of host responses toward combination products.

Adverse effects of biologics used for treating IBD

In the last decade, biologic agents, in particular anti-TNF agents such as infliximab, adalimumab, and certolizumab have substantially extended the therapeutic armamentarium of inflammatory bowel disease (IBD). Additional approaches include biologicals, such as natalizumab, that block leucocyte adhesion; those that target cytokines, such as interleukin-12/23 antibodies; or those that inhibit T-cell signaling, such as interleukin-6 receptor antibodies. However, these drugs have a number of contraindications and side effects, especially when used in combination with classical immunosuppressive agents or corticosteroids. Areas of concern include opportunistic infections, malignancies, and miscellaneous complications such as injection/infusion reactions and autoimmunity and contraindications, such as heart failure and acute infectious diseases. In this review, the indications of biologicals in IBD treatment are briefly reported, and the potential disadvantages of a more active therapeutic approach in IBD are discussed. We have learned in the last decade that anti-TNF-alpha therapy is an effective and relatively safe treatment option for selected patients that changes the natural course of severe IBD. However, despite these changed therapeutic paradigms and goals in IBD, clinicians should be aware that the powerful immunosuppressive capacity of biologicals necessitates a rigorous long-term safety follow-up.

Incidence and nature of infectious disease in patients treated with anti-TNF agents

Tumor necrosis factor alpha (TNF-alpha) inhibitors offer a targeted therapeutic strategy that contrasts with the nonspecific immunosuppressive agents traditionally used to treat most inflammatory diseases. These biologic agents have had a significant impact in ameliorating the signs and symptoms of inflammatory rheumatoid disease and improving patient function. From the onset of clinical trials, a central concern of cytokine blockade has been a potential increase in susceptibility to infections. Not surprisingly, a variety of infections have been reported in association with the use of TNF-alpha inhibitor agents. In particular, there is evidence suggesting an increased rate of granulomatous infections in patients treated with monoclonal TNF-alpha inhibitors. This review provides the incidence and nature of infections in patients treated with TNF-alpha inhibitor agents and reminds the clinician of the required vigilance in monitoring patients.

Tumor necrosis factor inhibitors and infection complications

Rheumatoid arthritis patients are at heightened risk for infections because of intrinsic disease severity with associated inflammation, comorbid illnesses, and use of glucocorticoids and various immunosuppressives. Although several studies have reported up to a twofold increase in risk of serious infections in RA patients treated with anti-tumor necrosis factor-alpha agents, results from other studies have been conflicting. Comparing results from different studies is challenging because of differences in patient populations, heterogeneous prevalence of comorbidities, and differing patterns of concomitant medication use. Based on available evidence, an excess risk for infection occurs early after initiation of tumor necrosis factor-alpha inhibitor therapy. Additionally, special circumstances such as surgical procedures may increase infection risk. The appropriate use of biologics in the perioperative setting remains empiric at best.

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.

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.

The intriguing biology of the tumour necrosis factor/tumour necrosis factor receptor superfamily: players, rules and the games

The members of the tumour necrosis factor (TNF)/tumour necrosis factor receptor (TNFR) superfamily are critically involved in the maintenance of homeostasis of the immune system. The biological functions of this system encompass beneficial and protective effects in inflammation and host defence as well as a crucial role in organogenesis. At the same time, members of this superfamily are responsible for host damaging effects in sepsis, cachexia, and autoimmune diseases. This review summarizes recent progress in the immunobiology of the TNF/TNFR superfamily focusing on results obtained from animal studies using gene targeted mice. The different modes of signalling pathways affecting cell proliferation, survival, differentiation, apoptosis, and immune organ development as well as host defence are reviewed. Molecular and cellular mechanisms that demonstrate a therapeutic potential by targeting individual receptors or ligands for the treatment of chronic inflammatory or autoimmune diseases are discussed.

Listeria Meningitis Associated with Infliximab

OBJECTIVE:

To report a case of Listeria monocytogenes meningitis in a 73-year-old man receiving infliximab for rheumatoid arthritis.

CASE SUMMARY:

A 73-year-old white man taking infliximab for rheumatoid arthritis developed listeria meningitis following his second dose. He was receiving other immunosuppressants; however, these remained constant immediately prior to the infection. Diagnosis was confirmed with L. monocytogenes isolated in the cerebrospinal fluid. The patient received 21 days of antibiotic therapy and recovered without any complications.

DISCUSSION:

L. monocytogenes is a gram-positive, non—spore-forming rod that has been associated with the ingestion of undercooked foods. This organism can cause sepsis or meningitis; however, immunocompromised patients, elderly patients, pregnant women, and neonates appear to be at greater risk for this type of infection. Tumor-necrosis factor-α (TNF-α) plays an important role in resistance to this type of infection, and listeria infections have been reported in 26 patients receiving TNF-α inhibitors. In our patient, the listeria infection occurred following his second course of infliximab, which provides a temporal relationship between the listeria infection and infliximab. However, his underlying rheumatoid arthritis and chronic steroid therapy would also increase his risk for a listeria infection.

CONCLUSIONS:

The listeria infection in our patient was a possible adverse event of infliximab according to the Naranjo probability scale. Because the majority of listeria infections occur in patients who are immunosuppressed, it would be reasonable to provide education for healthcare professionals on preventing these infections in all patients receiving immunosuppressants, including anti—TNF-α therapy. Those at risk due to their underlying health conditions should also be monitored closely.

Biological functions of tumor necrosis factor cytokines and their receptors

Tumor necrosis factor (TNF; formerly known as TNFalpha) and lymphotoxin (LT)alpha, originally characterized by their ability to induce tumor cell apoptosis and cachexia, are now considered as central mediators of a broad range of biological activities. These activities encompass beneficial effects for the host in inflammation and in protective immune responses against a variety of infectious pathogens. TNF family members on the other hand also exert host-damaging effects in sepsis, in tumor cachexia as well as in autoimmune diseases. In addition, the essential roles of the core members of the TNF superfamily, LTalpha, LTbeta, TNF, and LIGHT as well as their receptors during the organogenesis of secondary lymphoid organs and the maintenance of the architecture of lymphatic tissues now becomes appreciated. The elucidation of the biological functions of these cytokines and their specific cell surface receptors has been crucially advanced by the study of gene-targeted mouse strains. This presentation summarizes the roles of TNFR and TNF-like cytokines in infection, sepsis and autoimmunity as well as the pivotal involvement of these molecules in the development of secondary lymphoid organs.

Adaptive immunity against Listeria monocytogenes in the absence of type I tumor necrosis factor receptor p55

Tumor necrosis factor (TNF) and the type I TNF receptor (TNFRI), p55, are critical for resistance against primary infections with the intracellular bacterial pathogen Listeria monocytogenes. Importantly, however, susceptibility to primary listeriosis in cytokine-deficient mice does not preclude the development or expression of effective adaptive immunity against virulent L. monocytogenes. We used TNFRI(-/-) mice to study adaptive antilisterial immunity in the absence of interactions between TNF and TNFRI. Our experiments indicate that TNFRI(-/-) mice survive and clear high-dose challenges with an attenuated strain of L. monocytogenes that is incapable of cell-to-cell spread. Furthermore, TNFRI(-/-) mice immunized with attenuated L. monocytogenes go on to develop potent adaptive immunity to subsequent high-dose challenges with virulent L. monocytogenes. Interestingly, CD8(+) T-cell depletion in vivo inhibits immunity to L. monocytogenes in the spleen but not in the liver of TNFRI(-/-) mice. The adaptive immune response in these animals is characterized by activation of listeriolysin O-specific CD8(+) T cells, which are capable of transferring antilisterial immunity to naive wild-type C57BL/6 host mice. These experiments demonstrate the development and expression of potent CD8(+) T-cell-mediated antilisterial immunity in the absence of TNFRI.

Reduced antilisterial activity of TNF-deficient bone marrow-derived macrophages is due to impaired superoxide production

Mice deficient for TNF ligand and receptor type 1 have demonstrated the importance of TNF in the host defense against Listeria monocytogenes. To investigate the particular deficiency of macrophages derived from TNF/lymphotoxin (LT)-alpha(-/-) mice in antilisterial growth control, bone marrow-derived macrophages (BMDM) were used for in vitro infection experiments. After the combined treatment with IFN-gamma and lipopolysaccharide (LPS), production of NO by wild-type (wt) and TNF/LT-alpha(-/-) BMDM was induced to comparable levels, but only wt BMDM controlled L. monocytogenes growth efficiently. Nevertheless, inhibition of NO production led to a remarkable loss of antilisterial activity. This suggests that presence of NO is necessary but not sufficient for L. monocytogenes killing and that elimination of L. monocytogenes requires additional effector molecules. The LPS-inducible superoxide production of TNF/LT-alpha(-/-) BMDM was impaired. Accordingly both scavenging of superoxide and peroxynitrite led to reduced L. monocytogenes killing by wt BMDM. In addition, peroxynitrite was able to kill L. monocytogenes in vitro. Together these findings suggest that the defective host defense of TNF/LT-alpha-deficient mice against L. monocytogenes partially stems from reduced superoxide production of macrophages due to the absence of TNF and imply a function for peroxynitrite, the reaction product of NO and superoxide, in the intracellular killing of L. monocytogenes.

Macrophage-lymphocyte interactions mediate anti-Burkholderia pseudomallei activity

The mechanisms involved in the pathogenesis of melioidosis, caused by the intracellular bacterium Burkholderia pseudomallei, are unclear. C57BL/6 mice are resistant to infection, while BALB/c mice are highly susceptible. Previous studies have demonstrated that peritoneal exudate cell preparations enriched for macrophages are capable of effectively eliminating intracellular pathogens. In this study we present evidence showing that interaction of macrophages with lymphocytes is necessary for efficient anti-B. pseudomallei activity.

Anthrax edema toxin differentially regulates lipopolysaccharide-induced monocyte production of tumor necrosis factor alpha and interleukin-6 by increasing intracellular cyclic AMP

Bacillus anthracis exotoxins mediate most of the symptomatology of severe anthrax. In addition to a clinical syndrome reminiscent of septic shock, which may be mediated by cytokines produced by macrophages stimulated with lethal toxin, infected patients show profound edema at sites of infection. Edema is mediated by edema toxin (ET), which comprises of a binding molecule, protective antigen, and an active moiety, edema factor, which possesses intrinsic adenylyl cyclase activity. Intracellular cyclic AMP (cAMP) regulates the production of several cytokines that modulate edema formation and play important roles in host defense against invading bacteria. To determine whether ET enhanced the accumulation of cAMP in monocytes and thereby influenced cytokine production, we cultured human monocytes with endotoxin (lipopolysaccharide [LPS]) and dilutions of ET and determined the levels of interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-alpha) in culture supernatant fluids. We further estimated cytokine-specific mRNA accumulation in monocytes by reverse transcription PCR and examined intracellular cAMP concentrations following treatment with ET. ET and LPS each induced monocytes to secrete comparable amounts of IL-6. ET did not inhibit and in most experiments modestly enhanced LPS-induced IL-6 production. In contrast to this stimulatory effect on IL-6 production, ET induced little or no TNF-alpha production. Moreover, ET profoundly inhibited LPS-induced TNF-alpha synthesis. These regulatory phenomena were also observed at the mRNA level in association with dose-related enhancement of intracellular cAMP in ET-treated monocytes. Monocytes treated with dibutyryl cAMP, an active analog of cAMP, produced cytokines in a pattern identical to that of cells treated with ET. The disruption of cytokine networks as a consequence of unregulated, ET-induced cAMP accumulation in human monocytes may impair cellular antimicrobial responses and contribute to clinical signs and symptoms.

Mice deficient for the 55 kd tumor necrosis factor receptor are resistant to endotoxic shock, yet succumb to L. monocytogenes infection

The multiple biological activities of tumor necrosis factor (TNF) are mediated by two distinct cell surface receptors of 55 kd (TNFRp55) and 75 kd (TNFRp75). Using gene targeting, we generated a TNFRp55-deficient mouse strain. Cells from TNFRp55-/-mutant mice lack expression of TNFRp55 but display normal numbers of high affinity TNFRp75 molecules. Thymocyte development and lymphocyte populations are unaltered, and clonal deletion of potentially self-reactive T cells is not impaired. However, TNF signaling is largely abolished, as judged by the failure of TNF to induce NF-kappa B in T lymphocytes from TNFRp55-deficient mice. The loss of TNFRp55 function renders mice resistant to lethal dosages of either lipopolysaccharides or S. aureus enterotoxin B. In contrast, TNFRp55-deficient mice are severely impaired to clear L. monocytogenes and readily succumb to infection. Thus, the 55 kd TNFR plays a decisive role in the host's defense against microorganisms and their pathogenic factors.

Alpha-naphthyl acetate esterase-1 (ANAE-1) secreted by epithelioid cells from induced rabbit lung granuloma showed MIF activity

The function of alpha-naphthyl acetate esterase-1, whose isoelectric point values range from 5.15 to 5.45, was examined. A higher value of alpha-naphthyl acetate esterase-1 was detected in the extracts of epithelioid cells isolated from rabbit lung granuloma at 4 weeks after injection of Freund's complete adjuvant, compared to those values of alveolar macrophages isolated from the same lungs described above and of the normal lungs. Additionally, this enzyme activity was observed to be prominent in the culture supernatants of epithelioid cells. alpha-Naphthyl acetate esterase-1 was purified from lung granuloma as a single 62-kDa band by SDS-PAGE analysis. The purified enzyme showed a macrophage migration inhibition activity at concentrations over 20 nM, and its activity was dose-dependent. Moreover, when various amounts of the purified enzyme were added to lymphocyte-derived macrophage migration inhibitory factor, macrophage migration inhibition was significantly enhanced with a dose-dependent manner. The results suggest that alpha-naphthyl acetate esterase-1 secreted by granuloma macrophages, particularly by epithelioid cells, contributes to granuloma formation.

Early activation of splenic macrophages by tumor necrosis factor alpha is important in determining the outcome of experimental histoplasmosis in mice

Experimental infection of animals with Histoplasma capsulatum caused a massive macrophage infiltration into the spleen and induced the production of tumor necrosis factor alpha (TNF-alpha) locally. The cytokine was also produced in vitro by peritoneal exudate macrophages exposed to a large inoculum of yeast cells. Depletion of the cytokine by injection of polyclonal sheep anti-TNF-alpha antibody was detrimental to sublethally infected mice. Fungous burdens in the spleens of TNF-alpha-depleted mice were higher than they were in the infected control mice at days 2, 7, and 9 after infection, and the antibody-treated animals succumbed to the infection. Histopathological study of spleen sections revealed that splenic macrophages were not able to control proliferation of intracellular yeasts as a result of TNF-alpha depletion. It seems that TNF-alpha plays a role in early activation of splenic macrophages which is important in controlling the outcome of an infection.

Activation of mononuclear immune cells in response to staphylococcal lipoteichoic acid

The goal of the present study was to evaluate the influence of staphylococcal lipoteichoic acid (LTA) on the activation of mononuclear immune cells. A murine tumor necrosis-like factor (TNF-like) was induced in the sera of CD-1 mice which had been primed with heat/formalin-inactivated Propionibacterium avidum KP-40 and subsequently exposed to LTA extracted from Staphylococcus saprophyticus strain S 1. Monoclonal antibody against murine TNF (anti-TNF) significantly inhibited the cytostatic activity of mice sera against transformed L-929 cells. Freshly isolated lymphocytes did not display interleukin 2 (Il-2) receptors, but receptors were expressed on Con A incubated cells and in significantly higher numbers after coexposure to staphylococcal LTA in vitro. Since the induction of TNF (macrophages) and Il-2 receptors (lymphocytes) represent stimulation of the mononuclear immune system, staphylococcal LTA may be considered to be an immunomodifier.