Outside-to-inside signal through the membrane TNF-alpha induces E-selectin (CD62E) expression on activated human CD4+ T cells

CD40L modulates CD4+ T-cell activation through receptor for activated C kinase 1

Inhibition of the co-stimulatory ligand CD40L has shown beneficial effects in many experimental models of autoimmune disease and inflammation. Here, we show that CD40L deficiency in T cells in mice causes a reduction of CD4+ T-cell activation and specifically a strong reduction in IFN-γ-producing Th1 cells. In vitro, we could not reproduce this antigen presenting cell-dependent effects, but found that T-cell CD40L affects cell death and proliferation. We identified receptor of activated C kinase, the canonical PKC binding partner and known to drive proliferation and apoptosis, as a mediator of CD40L reverse signaling. Furthermore, we found that CD40L clustering stabilizes IFN-γ mediated Th1 polarization through STAT1, a known binding partner of receptor of activated C kinase. Together this highlights the importance of both CD40L forward and reverse signaling.

The expression pattern of membranous TNF-α is distinct from its intracellular form in the breast cancer draining lymph nodes

Tumor necrosis factor-alpha (TNF-α) is mostly known as a soluble cytokine. However, this study focused on its membranous form whose significance is rarely investigated in antitumor immunity. Herein, we assessed the expression of both membranous and intracellular forms of TNF-α (m/icTNF-α) in the lymphocytes derived from breast cancer-draining lymph nodes. CD4⁺T cells were the main subset expressing mTNF-α with the highest intensity, whereas icTNF-α expression was most intense in CD8⁺T cells. An inverse correlation was seen between the frequency of mTNF-α and the expression intensity of this cytokine in B cells. In the clinical context, the higher intensity of mTNF-α expression in CD19⁺ cells correlated with poor prognosticators, while the frequency of mTNF-α⁺CD19⁺ cells showed a reverse correlation with the number of involved lymph nodes. The two forms of TNF-α did not show similar associations with cancer parameters, which highlights the complex role of this cytokine in breast cancer immunity.

Tumor Necrosis Factor-α: The Next Marker of Stroke

Although there is no shortage of research on the markers for stroke, to our knowledge, there are no clear markers that can meet the needs of clinical prediction and treatment. The inflammatory cascade is a critical process that persists and functions throughout the stroke process, ultimately worsening stroke outcomes and increasing mortality. Numerous inflammatory factors, including tumor necrosis factor (TNF), are involved in this process. These inflammatory factors play a dual role during stroke, and their mechanisms are complex. As one of the representatives, TNF is the primary regulator of the immune system and plays an essential role in the spread of inflammation. In researches done over the last few years, tumor necrosis factor-alpha (TNF-α) has emerged as a potential marker for stroke because of its essential role in stroke. This review summarizes the latest research on TNF-α in stroke and explores its potential as a therapeutic target.

Differential impacts of TNFα inhibitors on the transcriptome of Th cells

BACKGROUND

Targeting TNFα is beneficial in many autoimmune and inflammatory diseases, including rheumatoid arthritis. However, the response to each of the existing TNFα inhibitors (TNFis) can be patient- and/or disease-dependent. In addition, TNFis can induce the production of type 1 interferons (IFNs), which contribute to their non-infection side effects, such as pustular psoriasis. Thus far, the molecular mechanisms mediating the drug-specific effects of TNFis and their induction of type 1 IFNs are not fully understood.

METHODS

Peripheral blood mononuclear cells (PBMCs) were collected from healthy donors and stimulated in vitro with anti-CD3 and anti-CD28 in the absence or presence of adalimumab, etanercept, or certolizumab. Th cells were isolated from the stimulated PBMCs, and their RNA was subjected to RNA-seq and quantitative polymerase chain reaction.

RESULTS

Adalimumab and etanercept, which contain Fc, but not certolizumab, which does not contain Fc, inhibited the expression of several effector cytokines by Th cells within anti-CD3/anti-CD28-stimulated PBMCs. Transcriptomic analyses further showed that adalimumab, but not certolizumab, reciprocally induced type 1 IFN signals and the expression of CD96 and SIRPG in Th cells. The unique effects of adalimumab were not due to preferential neutralization of soluble TNFα but instead were mediated by several distinct mechanisms independent or dependent of Fc-facilitated physical interaction between Th cells and CD14+ monocytes.

CONCLUSIONS

TNFis can have drug-specific effects on the transcriptional profile of Th cells.

C-tag TNF: a reporter system to study TNF shedding

TNF is a highly pro-inflammatory cytokine that contributes not only to the regulation of immune responses but also to the development of severe inflammatory diseases. TNF is synthesized as a transmembrane protein, which is further matured via proteolytic cleavage by metalloproteases such as ADAM17, a process known as shedding. At present, TNF is mainly detected by measuring the precursor or the mature cytokine of bulk cell populations by techniques such as ELISA or immunoblotting. However, these methods do not provide information on the exact timing and extent of TNF cleavage at single-cell resolution and they do not allow the live visualization of shedding events. Here, we generated C-tag TNF as a genetically encoded reporter to study TNF shedding at the single-cell level. The functionality of the C-tag TNF reporter is based on the exposure of a cryptic epitope on the C terminus of the transmembrane portion of pro-TNF on cleavage. In both denatured and nondenatured samples, this epitope can be detected by a nanobody in a highly sensitive and specific manner only upon TNF shedding. As such, C-tag TNF can successfully be used for the detection of TNF cleavage in flow cytometry and live-cell imaging applications. We furthermore demonstrate its applicability in a forward genetic screen geared toward the identification of genetic regulators of TNF maturation. In summary, the C-tag TNF reporter can be employed to gain novel insights into the complex regulation of ADAM-dependent TNF shedding.

In vitro Evaluation of the Safety of Adalimumab for the Eye Under HTLV-1 Infection Status: A Preliminary Study

Adalimumab (ADA), a fully human monoclonal tumor necrosis factor (TNF)-α antibody, is one of the most widely used biologics in the treatment of inflammatory diseases. However, ADA can exacerbate infectious conditions, induce paradoxical reactions such as inflammation, and cause neoplasia. Human T-cell leukemia virus type 1 (HTLV-1) is an infectious agent that induces inflammation and neoplastic infiltration in the eye. To date, numerous HTLV-1 carriers have been treated with adalimumab to suppress inflammation out of necessity, when standard anti-inflammatory drugs such as steroids and immunosuppressive agents have proven inadequate to control the inflammation. Here, we clarify the safety of adalimumab for the eye under HTLV-1 infectious conditions in vitro. We used the adult retinal pigment epithelial cell line (ARPE)-19 cell line as ocular resident cells, and used MT2 and TL-Om1 as HTLV-1-infected cells. ARPE-19 and MT2/TL-Om1 were co-cultured, and then adalimumab was administered. Production of cytokines and chemokines, TNF-α receptor (TNF-R), HTLV-1 proviral load (PVL), and apoptosis were measured to assess the effects of adalimumab. Contact between ARPE-19 and MT2/TL-Om1 produced inflammatory cytokines such as TNF, interleukin (IL)-6, IL-8 and IL-10, and transduced chemokines such as interferon-inducible protein-10 (IP-10), monocyte chemotactic protein-1 (MCP-1), monokine induced by interferon-γ (MIG), and regulated on activation, normal T cell expressed and secreted (RANTES). No inflammatory cytokines and chemokines were exacerbated by adalimumab. Expression of TNF-R on ARPE-19 and MT2/TL-Om1 cells, HTLV-1 PVLs of MT2/TL-Om1 cells, and cell growth rate and apoptotic rate of ARPE-19 were unaffected by adalimumab. In conclusion, adalimumab does not appear to exacerbate HTLV-1-associated inflammatory conditions in the eye or increase PVL in HTLV-1-infected T cells. These data suggest that adalimumab could be used safely for the eye under HTLV-1 infectious conditions from the perspective of in vitro assessment.

TNF-Mediated Homeostatic Synaptic Plasticity: From in vitro to in vivo Models

Since it was first described almost 30 years ago, homeostatic synaptic plasticity (HSP) has been hypothesized to play a key role in maintaining neuronal circuit function in both developing and adult animals. While well characterized in vitro, determining the in vivo roles of this form of plasticity remains challenging. Since the discovery that the pro-inflammatory cytokine tumor necrosis factor-α (TNF-α) mediates some forms of HSP, it has been possible to probe some of the in vivo contribution of TNF-mediated HSP. Work from our lab and others has found roles for TNF-HSP in a variety of functions, including the developmental plasticity of sensory systems, models of drug addiction, and the response to psychiatric drugs.

Methotrexate Enhances Apoptosis of Transmembrane TNF-Expressing Cells Treated With Anti-TNF Agents

Background

Concomitant use of methotrexate (MTX) improves the clinical efficacy of anti-TNF agents in the treatment of rheumatoid arthritis (RA). We aimed to clarify the cytotoxic effect of MTX on transmembrane TNF (tmTNF)-expressing cells treated with anti-TNF agents.

Methods

Jurkat T cells stably expressing tmTNF were used for the following experiments. Cytotoxicity induced by an anti-TNF agent (infliximab, adalimumab, or certolizumab pegol) with concomitant MTX were compared with that by MTX alone or by an anti-TNF agent alone using flow cytometry. Apoptosis-induction mediated by reverse signal through tmTNF, complement-dependent cytotoxicity (CDC), antibody-dependent cell-mediated cytotoxicity (ADCC), and antibody-dependent cellular phagocytosis (ADCP) were evaluated. Folic acid and Y-27632, a Rho kinase inhibitor, were used as inhibitors to study intracellular signaling pathway in apoptosis induced by MTX and anti-TNF agents.

Results

Apoptosis of tmTNF-expressing cells was significantly increased by the concomitant administration of MTX and an anti-TNF agent, compared with MTX alone or an anti-TNF agent alone. The apoptosis induction by concomitant MTX was most pronounced in infliximab-treatment. Reverse signal transduction, but not CDC or ADCC/ADCP, was responsible for the coordinate effect of MTX and an anti-TNF agent on tmTNF-expressing cells. Folic acid inhibited MTX-mediated apoptosis, while Y-27632 suppressed JNK activation and infliximab-induced apoptosis via revere signal through tmTNF.

Conclusion

The apoptotic effect was enhanced by combination of MTX and an anti-TNF agent in tmTNF-expressing cells. The intracellular pathways induced by MTX and anti-TNF agents seem to be independent. These findings might explain at least in part improved the clinical response upon co-therapy of MTX and an anti-TNF agent in RA.

Tumor Necrosis Factor α Blockade: An Opportunity to Tackle Breast Cancer

Breast cancer is the most frequently diagnosed cancer and the principal cause of mortality by malignancy in women and represents a main problem for public health worldwide. Tumor necrosis factor α (TNFα) is a pro-inflammatory cytokine whose expression is increased in a variety of cancers. In particular, in breast cancer it correlates with augmented tumor cell proliferation, higher malignancy grade, increased occurrence of metastasis and general poor prognosis for the patient. These characteristics highlight TNFα as an attractive therapeutic target, and consequently, the study of soluble and transmembrane TNFα effects and its receptors in breast cancer is an area of active research. In this review we summarize the recent findings on TNFα participation in luminal, HER2-positive and triple negative breast cancer progression and metastasis. Also, we describe TNFα role in immune response against tumors and in chemotherapy, hormone therapy, HER2-targeted therapy and anti-immune checkpoint therapy resistance in breast cancer. Furthermore, we discuss the use of TNFα blocking strategies as potential therapies and their clinical relevance for breast cancer. These TNFα blocking agents have long been used in the clinical setting to treat inflammatory and autoimmune diseases. TNFα blockade can be achieved by monoclonal antibodies (such as infliximab, adalimumab, etc.), fusion proteins (etanercept) and dominant negative proteins (INB03). Here we address the different effects of each compound and also analyze the use of potential biomarkers in the selection of patients who would benefit from a combination of TNFα blocking agents with HER2-targeted treatments to prevent or overcome therapy resistance in breast cancer.

Biomphalaria glabrata immunity: Post-genome advances

The freshwater snail, Biomphalaria glabrata, is an important intermediate host in the life cycle for the human parasite Schistosoma mansoni, the causative agent of schistosomiasis. Current treatment and prevention strategies have not led to a significant decrease in disease transmission. However, the genome of B. glabrata was recently sequenced to provide additional resources to further our understanding of snail biology. This review presents an overview of recently published, post-genome studies related to the topic of snail immunity. Many of these reports expand on findings originated from the genome characterization. These novel studies include a complementary gene linkage map, analysis of the genome of the B. glabrata embryonic (Bge) cell line, as well as transcriptomic and proteomic studies looking at snail-parasite interactions and innate immune memory responses towards schistosomes. Also included are biochemical investigations on snail pheromones, neuropeptides, and attractants, as well as studies investigating the frontiers of molluscan epigenetics and cell signaling were also included. Findings support the current hypotheses on snail-parasite strain compatibility, and that snail host resistance to schistosome infection is dependent not only on genetics and expression, but on the ability to form multimeric molecular complexes in a timely and tissue-specific manner. The relevance of cell immunity is reinforced, while the importance of humoral factors, especially for secondary infections, is supported. Overall, these studies reflect an improved understanding on the diversity, specificity, and complexity of molluscan immune systems.

The Proton-Sensing GPR4 Receptor Regulates Paracellular Gap Formation and Permeability of Vascular Endothelial Cells

GPR4 is a pH-sensing G protein-coupled receptor highly expressed in vascular endothelial cells and can be activated by protons in the inflamed tissue microenvironment. Herein, we report that acidosis-induced GPR4 activation increases paracellular gap formation and permeability of vascular endothelial cells through the G_α12/13/Rho GTPase signaling pathway. Evaluation of GPR4 in the inflammatory response using the acute hindlimb ischemia-reperfusion mouse model revealed that GPR4 mediates tissue edema, inflammatory exudate formation, endothelial adhesion molecule expression, and leukocyte infiltration in the inflamed tissue. Genetic knockout and pharmacologic inhibition of GPR4 alleviate tissue inflammation. These results suggest GPR4 is a pro-inflammatory receptor and could be targeted for therapeutic intervention.

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Acidosis/GPR4 regulates endothelial paracellular gap formation and permeability

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GPR4 exacerbates inflammation by increasing tissue edema and leukocyte infiltration

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Pharmacological inhibition of GPR4 reduces inflammatory responses

Pharmacological inhibition of GPR4 remediates intestinal inflammation in a mouse colitis model

Inflammatory bowel disease (IBD) is characterized by chronic, recurring inflammation of the digestive tract. Current therapeutic approaches are limited and include biologics and steroids such as anti-TNFα monoclonal antibodies and corticosteroids, respectively. Significant adverse drug effects can occur for chronic usage and include increased risk of infection in some patients. GPR4, a pH-sensing G protein-coupled receptor, has recently emerged as a potential therapeutic target for intestinal inflammation. We have assessed the effects of a GPR4 antagonist, 2-(4-((2-Ethyl-5,7-dimethylpyrazolo[1,5-a]pyrimidin-3-yl)methyl)phenyl)-5-(piperidin-4-yl)-1,3,4-oxadiazole (GPR4 antagonist 13, also known as NE-52-QQ57) in the dextran sulfate sodium (DSS)-induced acute colitis mouse model. The GPR4 antagonist 13 inhibited intestinal inflammation. The clinical parameters such as body weight loss and fecal score were reduced in the GPR4 antagonist 13 treatment group compared to vehicle control. Macroscopic disease indicators such as colon shortening, splenic expansion, and mesenteric lymph node enlargement were all reduced in severity in the GPR4 antagonist 13 treated mice. Histopathological features of active colitis were alleviated in GPR4 antagonist 13 treatment groups compared to vehicle control. Finally, inflammatory gene expression in the colon tissues and vascular adhesion molecule expression in the intestinal endothelia were attenuated by GPR4 antagonist 13. Our results indicate that GPR4 antagonist 13 provides a protective effect in the DSS-induced acute colitis mouse model, and inhibition of GPR4 can be explored as a novel anti-inflammatory approach.

Exercise and Cardiovascular Progenitor Cells

Autologous stem/progenitor cell-based methods to restore blood flow and function to ischemic tissues are clinically appealing for the substantial proportion of the population with cardiovascular diseases. Early preclinical and case studies established the therapeutic potential of autologous cell therapies for neovascularization in ischemic tissues. However, trials over the past ∼15 years reveal the benefits of such therapies to be much smaller than originally estimated and a definitive clinical benefit is yet to be established. Recently, there has been an emphasis on improving the number and function of cells [herein generally referred to as circulating angiogenic cells (CACs)] used for autologous cell therapies. CACs include of several subsets of circulating cells, including endothelial progenitor cells, with proangiogenic potential that is largely exerted through paracrine functions. As exercise is known to improve CV outcomes such as angiogenesis and endothelial function, much attention is being given to exercise to improve the number and function of CACs. Accordingly, there is a growing body of evidence that acute, short-term, and chronic exercise have beneficial effects on the number and function of different subsets of CACs. In particular, recent studies show that aerobic exercise training can increase the number of CACs in circulation and enhance the function of isolated CACs as assessed in ex vivo assays. This review summarizes the roles of different subsets of CACs and the effects of acute and chronic exercise on CAC number and function, with a focus on the number and paracrine function of circulating CD34+ cells, CD31+ cells, and CD62E+ cells. © 2019 American Physiological Society. Compr Physiol 9:767-797, 2019.

Targeting TNFR2 as a Novel Therapeutic Strategy for Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the most common cause of dementia. Accumulating experimental evidence shows the important linkage between tumor necrosis factor-α (TNF) and AD, but the exact role of TNF in AD is still not completely understood. Although TNF-inhibitors are successfully used for treating several diseases, total inhibition of TNF can cause side effects, particularly in neurological diseases. This is attributed to the opposing roles of the two TNF receptors. TNF receptor 1 (TNFR1) predominantly mediates inflammatory and pro-apoptotic signaling pathways, whereas TNF receptor 2 (TNFR2) is neuroprotective and promotes tissue regeneration. Therefore, the specific activation of TNFR2 signaling, either by directly targeting TNFR2 via TNFR2 agonists or by blocking TNFR1 signaling with TNFR1-selective antagonists, seems a promising strategy for AD therapy. This mini-review discusses the involvement of TNFR2 and its signaling pathway in AD and outlines its potential application as therapeutic target. A better understanding of the function of TNFR2 may lead to the development of a treatment for AD.

Anti-TNF Therapy in Crohn's Disease

Crohn’s disease (CD) accounts for a variety of clinical manifestations or phenotypes that stem from chronic inflammation in the gastrointestinal tract. Its worldwide incidence is increasing including younger or childhood-onset of disease. The natural history of Crohn’s disease is characterized by a remitting and relapsing course that progresses to complications and surgery in most patients. The goals of treatment are to achieve clinical and endoscopic remission, to avoid disease progression and minimise surgical resections. Medical treatment usually features antibiotics, corticosteroids, immunomodulators (thiopurines, methotrexate). Anti-TNF (tumour necrosis factor) therapy was approved for use in Crohn’s disease in 1998, and has changed the paradigm of treatment, leading to improved rates of response and remission in patients. There are significant considerations that need to be borne in mind, when treating patients including immunogenicity, safety profile and duration of treatment.

The Distribution of Activation Markers and Selectins on Peripheral T Lymphocytes in Preeclampsia

Introduction

Impaired maternal immune tolerance resulting in systemic inflammation plays a pivotal role in the pathogenesis of preeclampsia. Phenotypical changes of monocytes and neutrophil granulocytes have already been studied in preeclampsia, and some studies also included T lymphocyte activation markers; however, the results are controversial and a comprehensive analysis of activation markers is lacking. The characteristics of cellular adhesion molecules in preeclampsia are yet to be described.

Material and Methods

Peripheral blood samples of 18 preeclamptic patients and 20 healthy pregnant women in the third trimester were evaluated using flow cytometry to characterize the cell surface expression of T lymphocyte activation markers and selectins.

Results

We found an elevated ratio of HLA-DR and CD122-, CD62E-, and CD62L-expressing cells among the CD4+ T lymphocytes in PE in comparison to healthy pregnancy. No alterations were found in the prevalence of CD69-, CD25-, and CD62P-expressing lymphocytes and CD11c-expressing monocytes.

Conclusions

Our findings support the role of activated T lymphocytes and specific cell adhesion molecules in the pathogenesis of preeclampsia.

Intramembrane proteolysis within lysosomes

Regulated intramembrane proteolysis is of pivotal importance in a diverse set of developmental and physiological processes. Altered intramembrane substrate turnover may be associated with neurodegeneration, cancer and impaired immune function. In this review we will focus on the intramembrane proteases which have been localized in the lysosomal membrane. Members of the γ-secretase complex and γ-secretase activity are found in the lysosomal membrane and are discussed to contribute to intracellular amyloid β production. Mutant or deficient γ-secretase may cause disturbed lysosomal function. The signal peptide peptidase-like (SPPL) protease 2a is a lysosomal membrane component and cleaves CD74, the invariant chain of the MHC II complex, as well as FasL, TNF, ITM2B and TMEM106, type II transmembrane proteins involved in the regulation of immunity and neurodegeneration. Therefore, it can be concluded, that not only proteolysis within the lysosomal lumen but also within lysosomal membranes regulates important cellular functions and contributes essentially to proteostasis of membrane proteins what may become increasingly compromised in the aged individual.

Molecular mechanisms of action of anti-TNF-α agents - Comparison among therapeutic TNF-α antagonists

Tumor necrosis factor (TNF)-α is a potent pro-inflammatory and pathological cytokines in inflammatory diseases such as rheumatoid arthritis and inflammatory bowel diseases. Anti-TNF-α therapy has been established as an efficacious therapeutic strategy in these diseases. In clinical settings, three monoclonal anti-TNF-α full IgG1 antibodies infliximab, adalimumab, and golimumab, PEGylated Fab' fragment of anti-TNF-α antibody certolizumab pegol, extracellular domain of TNF receptor 2/IgG1-Fc fusion protein etanercept, are almost equally effective for rheumatoid arthritis. Although monoclonal full IgG1 antibodies are able to induce clinical and endoscopic remission in inflammatory bowel diseases, certolizumab pegol without Fc portion has been shown to be less effective for inflammatory bowel diseases compared to full IgG1 antibodies. In addition, there are no evidences that etanercept leads clinical remission in inflammatory bowel diseases. Besides the common effect of anti-TNF-α agents on neutralization of soluble TNF-α, each anti-TNF-α agent has its own distinctive pharmacological properties which cause the difference in clinical efficacies. Here we focus on the distinctions of action of anti-TNF-α agents especially in following points; (1) blocking ability against ligands, transmembrane TNF-α and lymphotoxin, (2) effects toward transmembrane TNF-α-expressing cells, (3) effects toward Fcγ receptor-expressing cells, (4) degradation and distribution in inflamed tissue. Accumulating evidence will give us the idea how to modify anti-TNF-α agents to enhance the clinical efficacy in inflammatory diseases.

TNF activity and T cells

TNF (tumor necrosis factor) is both a pro-inflammatory and anti-inflammatory cytokine that is central to the development of autoimmune disease, cancer, and protection against infectious pathogens. As well as a myriad other activities, TNF can be a product of T cells and can act on T cells. Here we review old and new data on the importance of TNF produced by T cells and how TNF signaling via TNFR2 may directly impact alternate aspects of T cell biology. TNF can promote the activation and proliferation of naïve and effector T cells, but also can induce apoptosis of highly activated effector T cells, further determining the size of the pathogenic or protective conventional T cell pool. Moreover, TNF can have divergent effects on regulatory T cells. It can both downregulate their suppressive capacity, but also contribute in other instances to their development or accumulation. Biologics that block TNF or stimulate TNFR2 therefore have the potential to strongly modulate the balance between effector T cells and Treg cells which could impact disease in both positive and negative manners.

New Insights into the Mechanisms of Action of Anti-Tumor Necrosis Factor-α Monoclonal Antibodies in Inflammatory Bowel Disease

Tumor necrosis factor alpha (TNF-α) has been widely accepted as a therapeutic target for inflammatory disorders including inflammatory bowel disease. Anti-TNF-α monoclonal antibodies (mAbs) including infliximab, adalimumab, golimumab, and certolizumab pegol have revolutionized therapy for these chronic inflammatory disorders. These agents are potent inhibitors of TNF-α, but significant evidence points to the fact that their actions extend beyond simple neutralization of the cytokine. Recent advances in understanding the mechanism of action of anti-TNF-α mAbs has discovered a number of previously unrecognized actions that are likely to be relevant in mediating their anti-inflammatory effects. Many of those actions are mediated by the binding of the antibodies to transmembrane TNF-α (tmTNF-α) and involve complex interactions with other molecular factors and cells. In this review, we have highlighted new information on the mechanism of actions of anti-TNF-α mAbs, from in vitro and in vivo studies. Despite obvious benefits in many patients, the clinical use of these antibodies are hampered by the fact that some patients do not respond to them, and among patients who do respond, many will develop recurrent disease despite continued dosing. Although pharmacokinetic factors explain some of the observed cases of partial or complete resistance to the effects of anti-TNF-α mAbs, other nonresponder patients may be resistant to those agents mechanism of action. A more thorough understanding of the mechanism of action of anti-TNF-α mAbs may allow the development of strategies to individualize therapy and to overcome resistance.

Balancing the risks and benefits of biologic therapy in inflammatory bowel diseases

INTRODUCTION

The incidence of Inflammatory Bowel Diseases (IBD) is rising and overall epidemiology is changing. Goals of IBD therapy are also fast changing to reflect the concept of mucosal healing. IBD management is increasingly revolving around questions of ideal positioning of biologic therapies.

AREAS COVERED

This paper covers important concepts regarding two classes of biologic medications approved for treatment of IBD in the United States - anti-TNF-α agents and lymphocyte-homing antagonists. Topics covered include drug mechanism of action, pharmacokinetic considerations for the clinician including therapeutic drug monitoring, summary of current evidence of drug efficacy in IBD focusing on randomized, controlled trial data. Additionally, nuanced discussion of medication side-effects and adverse reactions is presented.

EXPERT OPINION

Paradigms of treatment goals in IBD are changing with increasing focus on mucosal healing. Concomitantly, our understanding of important factors that impact drug pharmacokinetic/pharmacodynamics relationships with biologic agents has increased which will help eventually develop personalized algorithms to optimize the efficacy of these agents. Though direct head-to-head comparisons between these agents are lacking, biologic agents can be considered the safest and most effective therapies introduced for IBD.

Novel mechanisms of action of the biologicals in rheumatic diseases

Biological drugs targeting pro-inflammatory or co-stimulatory molecules or depleting lymphocyte subsets made a revolution in rheumatoid arthritis (RA) treatment. Their comparable efficacy in clinical trials raised the point of the heterogeneity of RA pathogenesis, suggesting that we are dealing with a syndrome rather than with a single disease. Several tumor necrosis factor-alpha (TNF-α) blockers are available, and a burning question is whether they are biosimilar or not. The evidence of diverse biological effects in vitro is in line with the fact that a lack of efficacy to one TNF-α agent does not imply a non-response to another one. As proteins, biologicals are potentially immunogenic. It has been recently raised that anti-drug antibodies (ADA) may affect their bioavailability and eventually the clinical efficacy through local formation of immune complexes and directly by preventing the interaction between the drug and TNF-α. Regular monitoring of drug and ADA levels appears the best way to tailor anti-TNF-α therapies. Owing to the pleiotropic characteristics of the target, anti-TNF-α blockers may affect several mechanisms beyond rheumatoid synovitis. As TNF-α plays a pivotal role in the induction of early atherosclerosis, treatment with TNF-inhibitors may modulate cholesterol handling, in particular, cholesterol efflux from macrophages. Side effects are a major issue because of the systemic TNF-α blocking action. The efficacy of an anti-C5 monoclonal antibody fused to a peptide targeting inflamed synovia in experimental arthritis opened the way for new strategies: Homing to the synovium of molecules neutralizing TNF would allow to maximize the therapeutic action avoiding the side effects.

Lack of TNF-alpha receptor type 2 protects motor neurons in a cellular model of amyotrophic lateral sclerosis and in mutant SOD1 mice but does not affect disease progression

Changes in the homeostasis of tumor necrosis factor α (TNFα) have been demonstrated in patients and experimental models of amyotrophic lateral sclerosis (ALS). However, the contribution of TNFα to the development of ALS is still debated. TNFα is expressed by glia and neurons and acts through the membrane receptors TNFR1 and TNFR2, which may have opposite effects in neurodegeneration. We investigated the role of TNFα and its receptors in the selective motor neuron death in ALS in vitro and in vivo. TNFR2 expressed by astrocytes and neurons, but not TNFR1, was implicated in motor neuron loss in primary SOD1-G93A co-cultures. Deleting TNFR2 from SOD1-G93A mice, there was partial but significant protection of spinal motor neurons, sciatic nerves, and tibialis muscles. However, no improvement of motor impairment or survival was observed. Since the sciatic nerves of SOD1-G93A/TNFR2-/- mice showed high phospho-TAR DNA-binding protein 43 (TDP-43) accumulation and low levels of acetyl-tubulin, two indices of axonal dysfunction, the lack of symptom improvement in these mice might be due to impaired function of rescued motor neurons. These results indicate the interaction between TNFR2 and membrane-bound TNFα as an innovative pathway involved in motor neuron death. Nevertheless, its inhibition is not sufficient to stop disease progression in ALS mice, underlining the complexity of this pathology. We show evidence of the involvement of neuronal and astroglial TNFR2 in the motor neuron degeneration in ALS. Both concur to cause motor neuron death in primary astrocyte/spinal neuron co-cultures. TNFR2 deletion partially protects motor neurons and sciatic nerves in SOD1-G93A mice but does not improve their symptoms and survival. However, TNFR2 could be a new target for multi-intervention therapies.

Restoration of peripheral blood natural killer and B cell levels in patients affected by rheumatoid and psoriatic arthritis during etanercept treatment

Etanercept (ETN) is an anti-tumour necrosis factor (TNF)-α agent used in rheumatoid arthritis (RA) and psoriatic arthritis (PsA). Few studies focused on the effects of anti-TNF-α on peripheral blood cells. We aimed to evaluate peripheral blood cells in RA and PsA patients during ETN treatment and to explore their relationships with disease activity. RA (n = 82) and PsA (n = 32) patients who started ETN were included into the study and evaluated prospectively before the beginning of ETN therapy and after 14, 22, 54 and 102 weeks. Patients were studied in terms of disease activity score on 28 joints (DAS28), clinical response and laboratory findings. Natural killer (NK) cells, B cells and T cells were characterized by immunophenotyping. Both the RA and the PsA patients showed reduced NK and B cell count before ETN treatment compared with controls. A negative correlation was demonstrated between DAS28 and B cell count in RA patients at baseline. Sustained significant increase of NK and B cells up to normal levels was observed in RA and PsA patients along ETN treatment. Increase of NK cell count was associated with a good-moderate clinical response to ETN in both RA and PsA patients. During ETN treatment peripheral blood NK and B cells levels were restored in RA and PsA patients. Correlations between NK and B cells with disease activity were observed, suggesting that those effects could be mediated by ETN treatment.

Inhibition of TNF receptor signaling by anti-TNFα biologicals primes naïve CD4(+) T cells towards IL-10(+) T cells with a regulatory phenotype and function

TNFα is a potent pro-inflammatory cytokine playing a pivotal role in several autoimmune diseases. Little is known about the mechanism of TNFα blocking agents on naïve T cell differentiation. Here, we report that neutralizing TNFα during priming of naïve CD4(+) T cells by dendritic cells favors development of IL-10(+) T helper cells. TNFα counteracts IL-10(+) T cell priming mainly via TNFRI receptor signaling. While initial T cell activation was not affected, neutralization of TNFα negatively affected sustained T cell differentiation in later stages of T cell priming. Whole genome gene expression analysis revealed an extended regulatory gene profile for anti-TNFα-treated T cells. Indeed, neutralizing TNFα during naïve T cell priming enhanced the suppressive function of anti-TNFα-treated T cells. Taken together, inhibition of TNFα-TNFR interaction shifts the balance of Th cell differentiation towards IL-10 expressing suppressive T cells, which may be one of the beneficial mechanisms in TNFα blocking therapies.

TNFα reverse signaling promotes sympathetic axon growth and target innervation

Reverse signaling via members of the tumor necrosis factor (TNF) superfamily controls multiple aspects of immune function. Here we document TNFα reverse signaling in the nervous system to our knowledge for the first time and show that it has a crucial role in establishing sympathetic innervation. During postnatal development, sympathetic axons express TNFα as they grow and branch in their target tissues, which in turn express TNF receptor 1 (TNFR1). In culture, soluble forms of TNFR1 act directly on postnatal sympathetic axons to promote growth and branching by a mechanism that depends on membrane-integrated TNFα and on downstream activation of ERK. Sympathetic innervation density is substantially lower in several tissues in postnatal and adult mice lacking either TNFα or TNFR1. These findings reveal that target-derived TNFR1 acts as a reverse-signaling ligand for membrane-integrated TNFα to promote growth and branching of sympathetic axons.

Mechanisms of action of anti-tumor necrosis factor α agents in Crohn's disease

Crohn's disease (CD) is characterized by inflammation that can affect any part of the gastrointestinal tract. It is a chronic destructive condition that follows a relapsing-remitting course and can lead to disability and a poor quality of life. Lifelong pharmacotherapy with systemic immunomodulator therapies remains the cornerstone of CD management. Advances in understanding of the immunopathogenic mechanisms underlying chronic gut inflammation in CD have led to the development of effective biological therapies for patients with CD. Tumor necrosis factor α (TNF-α) is a potent proinflammatory cytokine that plays a pivotal role in the development of Crohn's inflammation. Therapies designed to target this cytokine have revolutionized treatment of CD since their introduction in the late 1990s, thanks to their ability to induce and maintain remission, heal mucosa, reduce hospital admissions and surgical procedures, and restore quality of life. Despite widespread use of these therapies in CD, their precise mechanism of action remains unclear, although several different mechanisms have been proposed. This review summarizes the biology of the TNF-α cytokine and the development of biological therapies targeting TNF-α, and updates our current understanding of mechanisms of action of the commercially available anti-TNF-α therapies used in the treatment of CD.

The cytotoxic effects of certolizumab pegol and golimumab mediated by transmembrane tumor necrosis factor α

BACKGROUND

Anti-tumor necrosis factor α (anti-TNF-α) agents have been successfully applied for the treatment of rheumatoid arthritis, Crohn's disease, and other chronic inflammatory diseases. Not only the neutralization of soluble TNF-α but also the effect on transmembrane TNF-α is important mechanisms of action of anti-TNF-α agents. This study investigated the cytotoxic effects of new anti-TNF-α agents, certolizumab pegol and golimumab, which are mediated by transmembrane TNF-α.

METHODS

Transmembrane TNF-α-expressing Jurkat T cells that did not express TNF receptors were used. The binding ability of each anti-TNF-α agent to transmembrane TNF-α, antibody-dependent cell-mediated cytotoxicity, complement-dependent cytotoxicity, and the apoptotic effect were examined.

RESULTS

Certolizumab pegol and golimumab bound to transmembrane TNF-α. Golimumab induced antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity, which was comparable to infliximab and adalimumab. However, certolizumab pegol did not induce antibody-dependent cell-mediated cytotoxicity or complement-dependent cytotoxicity. Certolizumab pegol directly induced nonapoptotic cell death in transmembrane TNF-α-expressing cells. Golimumab induced a weaker apoptotic effect than infliximab and adalimumab.

CONCLUSIONS

The cytotoxic effects of anti-TNF-α agents on TNF-α-expressing cells are considered to be associated with the clinical effect of these agents on granulomatous diseases. The direct cytotoxic effect of certolizumab pegol on TNF-α-producing cells may contribute to its clinical efficacy in Crohn's disease. Golimumab may be less effective for granulomatous diseases.

Profile of certolizumab and its potential in the treatment of psoriatic arthritis

Psoriatic arthritis (PsA) is a chronic inflammatory arthropathy associated with psoriasis (PsO). PsA could be considered an enthesal disease because of the link between mechanical stress (entheses) and immunologically active tissue (synovium). Evidence of efficacy of anti-tumor necrosis factor alpha (TNF-α) is supported by reduction of histological vascularity and immune cell infiltrates in synovial tissue after treatment. Certolizumab pegol (CZP) is a polyethylene glycolylated (PEGylated) Fab' fragment of a humanized monoclonal antibody that binds and neutralizes human TNF-α. The PEG moiety of the Fab fragment, markedly increases the half-life of CZP and confers to the drug a unique structure that differs from the other anti-TNF-α agents tested for the treatment of Crohn's disease, rheumatoid arthritis, ankylosing spondylitis, axial spondyloarthritis, nonradiographic spondyloarthritis, PsO, and PsA. In contrast to other anti-TNF-α agents, CZP did not mediate increased levels of apoptosis, suggesting that these mechanisms are not essential for the anti-TNF-α efficacy in Crohn's disease. As CZP, infliximab, and adalimumab, but not etanercept, almost completely inhibited lipopolysaccharide-induced interleukin-1 beta release from monocytes, this cytokine-production inhibition may be relevant for drug efficacy. Due to these characteristics, it has been demonstrated in clinical studies that CZP effectively improves signs and symptoms of arthritis and physical function and skin manifestations of PsO, with a safety profile similar to rheumatoid arthritis. This drug can be considered as a valid treatment in patients affected by PsA. The efficacy and tolerability profiles suggest CZP as a suitable antipsoriatic drug in the treatment of PsA.

FCGR3A-158 polymorphism influences the biological response to infliximab in Crohn's disease through affecting the ADCC activity

An association between FCGR3A-158 V/F polymorphism and biological responses to infliximab has been reported in Crohn's disease (CD) in Western countries. However, little is known about the mechanism by which gene polymorphism affects the responses to infliximab. The aims of this study were to confirm the association in Japanese CD patients and to reveal the effect of gene polymorphism on biological responses to infliximab. Japanese CD patients were examined retrospectively at weeks 8 and 30. Clinical and biological responses were assessed by the Crohn's disease activity index and C-reactive protein levels, respectively. The infliximab-binding affinity of natural killer (NK) cells from FCGR3A-158 V/V, V/F and F/F donors was examined. Infliximab-mediated antibody-dependent cell-mediated cytotoxicity (ADCC) activities were also determined using transmembrane TNF-α-expressing Jurkat T cells as target cells and peripheral blood mononuclear cells (PBMCs) from V/V, V/F and F/F donors as effector cells. Biological responses at week 8 were statistically higher in V/V patients, whereas no significant differences were observed in either clinical responses at weeks 8 and 30 or biological responses at week 30 among the three genotypes. NK cells and PBMCs from V/V patients also showed higher infliximab-binding affinity and infliximab-mediated ADCC activity, respectively. Our results suggest that FCGR3A-158 polymorphism is a predicting factor of biological responses to infliximab in the early phases. FCGR3A-158 polymorphism was also found to affect the infliximab-binding affinity of NK cells and infliximab-mediated ADCC activity in vitro, suggesting that an effect on ADCC activity influences biological responses to infliximab in CD patients.

Targeting monocytes/macrophages in the treatment of rheumatoid arthritis

Biotherapies have revolutionized the treatment of RA. However, much work is needed to understand all the mechanisms of these biotherapies, and alternatives are needed to circumvent adverse effects and the high cost of these long-lasting treatments. In this article we outline some of the approaches we have used to target monocytes/macrophages as major components of inflammation and bone homeostasis. We also discuss how anti-TNF-α antibodies target monocytes/macrophages in the complex mechanisms contributing to inhibition of inflammation.

Historical perspectives on tumor necrosis factor and its superfamily: 25 years later, a golden journey

Although activity that induced tumor regression was observed and termed tumor necrosis factor (TNF) as early as the 1960s, the true identity of TNF was not clear until 1984, when Aggarwal and coworkers reported, for the first time, the isolation of 2 cytotoxic factors: one, derived from macrophages (molecular mass 17 kDa), was named TNF, and the second, derived from lymphocytes (20 kDa), was named lymphotoxin. Because the 2 cytotoxic factors exhibited 50% amino acid sequence homology and bound to the same receptor, they came to be called TNF-α and TNF-β. Identification of the protein sequences led to cloning of their cDNA. Based on sequence homology to TNF-α, now a total of 19 members of the TNF superfamily have been identified, along with 29 interacting receptors, and several molecules that interact with the cytoplasmic domain of these receptors. The roles of the TNF superfamily in inflammation, apoptosis, proliferation, invasion, angiogenesis, metastasis, and morphogenesis have been documented. Their roles in immunologic, cardiovascular, neurologic, pulmonary, and metabolic diseases are becoming apparent. TNF superfamily members are active targets for drug development, as indicated by the recent approval and expanding market of TNF blockers used to treat rheumatoid arthritis, psoriasis, Crohns disease, and osteoporosis, with a total market of more than US $20 billion. As we learn more about this family, more therapeutics will probably emerge. In this review, we summarize the initial discovery of TNF-α, and the insights gained regarding the roles of this molecule and its related family members in normal physiology and disease.

Psoriasis

Psoriasis is a common relapsing and remitting immune-mediated inflammatory disease that affects the skin and joints. This review focuses on current immunogenetic concepts, key cellular players, and axes of cytokines that are thought to contribute to disease pathogenesis. We highlight potential therapeutic targets and give an overview of the currently used immune-targeted therapies.

Tumor necrosis factor-alpha and the roles it plays in homeostatic and degenerative processes within the central nervous system

Tumor Necrosis Factor-alpha (TNF-α) is a prototypic pro-inflammatory cytokine involved in the innate immune response. TNF-α ligation and downstream signaling with one of its cognate receptors, TNF-RI or TNF-RII, modulates fundamental processes in the brain including synapse formation and regulation, neurogenesis, regeneration, and general maintenance of the central nervous system (CNS). During states of chronic neuroinflammation, extensive experimental evidence implicates TNF-α as a key mediator in disease progression, gliosis, demyelination, inflammation, blood-brain-barrier deterioration, and cell death. This review explores the complex roles of TNF-α in the CNS under normal physiologic conditions and during neurodegeneration. We focus our discussion on Multiple Sclerosis, Parkinson's disease, and Alzheimer's disease, relaying the outcomes of preclinical and clinical testing of TNF-α directed therapeutic strategies, and arguing that despite the wealth of functions attributed to this central cytokine, surprisingly little is known about the cell type- and stage-specific roles of TNF-α in these debilitating disorders.

Anti-TNF-α agents in the treatment of immune-mediated inflammatory diseases: mechanisms of action and pitfalls

TNF-α is a potent inducer of the inflammatory response, a key regulator of innate immunity and plays an important role in the regulation of Th1 immune responses against intracellular bacteria and certain viral infections. However, dysregulated TNF can also contribute to numerous pathological situations. These include immune-mediated inflammatory diseases (IMIDs) including rheumatoid arthritis, Crohn’s disease, psoriatic arthritis, ankylosing spondylitis, ulcerative colitis and severe chronic plaque psoriasis. Animal and human studies concerning the role of TNF-α in IMIDs have led to the development of a therapy based on TNF blockage. This article focuses first on the potential mechanisms by which the three currently licensed agents, adalimumab, etarnecept and infliximab, decrease the inflammatory activity of patients with different IMIDs. Second, it focuses on the risks, precautions and complications of the use of TNF-α inhibitors in these patients.

Transmembrane TNF-alpha: structure, function and interaction with anti-TNF agents

Transmembrane TNF-α, a precursor of the soluble form of TNF-α, is expressed on activated macrophages and lymphocytes as well as other cell types. After processing by TNF-α-converting enzyme (TACE), the soluble form of TNF-α is cleaved from transmembrane TNF-α and mediates its biological activities through binding to Types 1 and 2 TNF receptors (TNF-R1 and -R2) of remote tissues. Accumulating evidence suggests that not only soluble TNF-α, but also transmembrane TNF-α is involved in the inflammatory response. Transmembrane TNF-α acts as a bipolar molecule that transmits signals both as a ligand and as a receptor in a cell-to-cell contact fashion. Transmembrane TNF-α on TNF-α-producing cells binds to TNF-R1 and -R2, and transmits signals to the target cells as a ligand, whereas transmembrane TNF-α also acts as a receptor that transmits outside-to-inside (reverse) signals back to the cells after binding to its native receptors. Anti-TNF agents infliximab, adalimumab and etanercept bind to and neutralize soluble TNF-α, but exert different effects on transmembrane TNF-α-expressing cells (TNF-α-producing cells). In the clinical settings, these three anti-TNF agents are equally effective for RA, but etanercept is not effective for granulomatous diseases. Moreover, infliximab induces granulomatous infections more frequently than etanercept. Considering the important role of transmembrane TNF-α in granulomatous inflammation, reviewing the biology of transmembrane TNF-α and its interaction with anti-TNF agents will contribute to understanding the bases of differential clinical efficacy of these promising treatment modalities.

Development and characterization of a novel human in vitro blood-nerve barrier model using primary endoneurial endothelial cells

There are phenotypic and functional differences between vascular endothelium from different tissues and between microvascular and macrovascular endothelial cells (ECs) from the same tissue. Relatively little is known about the human blood-nerve barrier (BNB). We report the development of an in vitro BNB model using primary human endoneurial ECs freshly isolated and purified from decedent sciatic nerves via endoneurial stripping, connective tissue enzymatic digestion, and density centrifugation. Primary human endoneurial ECs are spindle shaped and contact inhibited. They rapidly differentiate to form capillary-like networks and microvessels, bind Ulex Europaeus Agglutinin 1 lectin, express von Willebrand factor, and endocytose acetylated low-density lipoprotein. They also express specific transport and cellular adhesion molecules and tight junction proteins, consistent with cells that form a highly restrictive endothelial barrier similar to the blood-brain barrier. When cultured on collagen-coated transwell inserts, the primary human endoneurial ECs develop an in vitro BNB with high transendothelial electrical resistances (160 Omega x cm(2); maximal 12 days after seeding) and low solute permeability coefficient to fluoresceinated high-molecular weight (70 kDa) dextran (2.75 x 10(-3) cm/minute). This in vitro BNB model retains essential known or expected characteristics of the human BNB and has many potential applications for studies of solute, macromolecule, microbial, virus, and leukocyte interactions with this highly specialized endothelial barrier.

Tumor necrosis factor alpha (TNF-alpha) levels in the brain and cerebrospinal fluid after meningitis induced by Streptococcus pneumoniae

Bacterial meningitis due to Streptococcus pneumoniae is associated with a significant mortality rate and persisting neurologic sequelae including sensory-motor deficits, seizures, and impairments of learning and memory. The presence of proliferating bacteria within the subarachnoid and ventricular space compartments triggers an intense inflammatory host response at killing the invading microorganism. Proinflammatory mediators released in the process include tumor necrosis factor alpha (TNF-alpha), interleukin (IL)-1beta, IL-6. TNF-alpha have several effects, including cytotoxicity, antiviral activity, transcription factor activation, and immune response regulation. Thus, the aim of this study was to verify the levels of the TNF-alpha after pneumococcal meningitis in male Wistar rats. The animals underwent a magna cistern tap receiving either 10 microL sterile saline as a placebo or an equivalent volume of a S. pneumoniae suspension at the concentration 5 x 10(9)cfu/mL. The animals were killed at 0, 6, 12, 24, 48 and 96 h after induction. The brain was removed and hippocampus, cortex, prefrontal and cerebrospinal fluid (CSF) were isolated and used for the determination of TNF-alpha levels. We found an increase in TNF-alpha levels at 6h after induction of the meningitis in the hippocampus (p<0.01), frontal cortex (p<0.05), and cerebrospinal fluid (p<0.001).There was no alteration in the cortex. Our data suggest that TNF-alpha is involved in the pathophysiology of the pneumococcal meningitis and could be investigated as a putative biomarker for brain damage in the first hours.

Comparisons of affinities, avidities, and complement activation of adalimumab, infliximab, and etanercept in binding to soluble and membrane tumor necrosis factor

The TNF antagonists adalimumab, infliximab, and etanercept are effective treatments for rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, and psoriasis, but only adalimumab and infliximab have been found to be efficacious in Crohn's disease. The present studies evaluated the TNF-binding and complement-activating properties of adalimumab, infliximab, and etanercept to determine whether these properties may explain differences in their clinical efficacy profiles. Association and dissociation rates of binding to soluble TNF were measured by surface plasmon resonance, and were found to be similar for adalimumab, infliximab, and etanercept, as were their calculated binding affinities. Avidity of binding to soluble TNF, measured by KinExA technology, was 10- to 20-fold greater for soluble etanercept (K(D)=0.4 picomolars [pM]) than for soluble adalimumab or infliximab (K(D)=8.6 and 4.2 pM, respectively). (125)I-adalimumab, -infliximab, and -etanercept bound to membrane TNF (mTNF) on mTNF-transfected cells with similar affinities (K(D)=483, 468, and 445 pM, respectively) that were each lower than for soluble TNF. Complement-dependent cytotoxicity (CDC) was induced in mTNF-transfected cells by adalimumab and infliximab, but was not induced in activated normal human PBMC by any of the 3 agents. In conclusion, the binding properties of adalimumab, infliximab, and etanercept were similar for soluble TNF, and very similar for mTNF, yet none of the 3 was able to induce CDC in activated PBMC. These results suggest that the different clinical efficacy profiles of these agents are not explained by differences in either TNF-intrinsic binding properties or complement lysis.

Influence of reverse signaling via membrane TNF-alpha on cytotoxicity of NK92 cells

Membrane tumor necrosis factor-alpha (mTNF-alpha) serves as a receptor transducing signals into mTNF-alpha-bearing cells. Among human peripheral blood mononuclear cells, natural killer (NK) cells have been reported to be the only cell type constitutively expressing mTNF-alpha, which is involved in the cytotoxicity of resting NK cells. Using an IL-2-dependent human NK cell line, NK92, which constitutively expresses mTNF-alpha, we examined the effect of reverse signaling via mTNF-alpha on cellular activities. When the cells were prestimulated with soluble TNFR1 (sTNFR1) which activated mTNF-alpha-mediated reverse signaling, the cytotoxicity of NK92 cells was significantly increased. Further investigation demonstrated that prestimulation with sTNFR1 augmented exocytosis and mRNA transcription of two cytotoxic molecules, perforin and granzyme B, which could serve as underlying molecular mechanisms by which mTNF-alpha-mediated reverse signaling promoted cytotoxicity of NK cells toward K562 cells. On the other hand, pretreatment of NK92 with sTNFR1 boosted the expression of FasL and TNF-alpha, including both the secretory and membrane forms. These molecules also contribute to the NK-mediated cytotoxicity, although K562 cells are Fas-negative and sTNF-alpha-resistant. Interestingly, the mTNF-alpha reverse signaling was found to act synergistically with IL-2 on NK-mediated cytotoxicity. This synergy markedly promoted the production of secretory as well as membrane cytotoxic molecules which may be responsible for the enhanced NK92-mediated cytotoxicity. Our observations suggest that, via reverse signaling, constitutively expressed mTNF-alpha may sensitize NK cells to activating stimuli, such as IL-2, resulting in increased NK-mediated cytotoxicity through promoting the production of multiple cytotoxic effector molecules.