Current Drug Targets - Inflammation & Allergy - Volume 4, Issue 2, 2005

Nitrosative stress and nitration of proteins in airway epithelium maybe responsible for steroid resistance in asthma and steroid ineffectiveness in chronic obstructive pulmonary disease (COPD), supporting the potential role of future therapeutic strategies aimed at regulating NO synthesis in asthma and COPD (for example, combination treatment with NOS inhibitors and corticosteroids). Here, the potential role of NO modulators (NO synthase inhibitors and NO donors) has been reviewed, which if are given on a regular basis may have clinical benefit in asthma and COPD.

In recent years, significant progress has been made in understanding the involvement of pro-inflammatory lipidic mediators in the pathogenesis of allergic diseases. The most relevant lipidic mediator is arachidonic acid and its metabolites. Arachidonic acid is the precursor for biosynthesis of eicosanoids, potent mediators of inflammation that have been implicated in the pathogenesis of diverse disease processes. Eicosanoids are mainly synthesized by the action of cyclo-oxygenase (prostaglandin endoperoxide synthase) that generates prostaglandins and thromboxane, and 5-lipoxygenase, which leads to the production of leukotrienes. In addition, 12- and 15-lipoxygenase are found in mammalian systems. The activity of these enzymes results in the formation of different hydroxyeicosatetraenoic acids, but their functions in vivo have not been clearly established in normal or pathological states. Since several arachidonic acid metabolites clearly play an important role in allergic response, a substantial effort has been directed to understanding the cellular and molecular aspects of these pathways and their pharmacological modulation. This review summarizes some of these aspects based on our current knowledge of the involvement of arachidonic metabolism in the pathogenesis of allergic diseases and outlines the potential therapeutic opportunities that can result from the modulation of these metabolites.

Essential role of β2-adrenoreceptor (β2AR) in airway relaxation is well established. Nevertheless, β2AR seems playing an actual role in allergy and inflammation. Interaction between β2AR and proinflamatory cytokines in airway smooth muscle has been revealed. Being located on proinflamatory cells, β2ARs may influence function of these cells in vivo. It was clear established, that stimulation of β2AR inhibits release of proinflamatory mediators from mast cells, influences T-cell growth and function, eosinophil survival and function, including GM-CSF- or PAF-induced degranulation. Stimulation of β2ARs, located on alveolar macrophages and epithelial cells, has ambiguity influence on their regulation and function, including phagocytosis and mediator secretion, in vivo. Vascular responses, resulting in inhibition of plasma exudation were confirmed, but modulation of sensory nerves via β2AR is not certain yet. β2AR-agonists are effective in treatment of immediate allergic reactions, but desensitisation of β2ARs on inflammatory cells may result in paradoxical effects, especially in asthma. In summary, it is clear that ?2ARs may play an anti-inflammatory role in vitro. Unfortunately, in vitro data have shown limited applicability in vivo; therefore further research in this field is required.

Asthma, atopic dermatitis, allergic rhinitis, which are amongst the most clinically relevant allergic disorders in industrialized countries affecting hundreds of millions of people world-wide, are characterized by tissue infiltration of Th2 cells, eosinophils, mast cells and basophils. Recruitment of these leukocyte subpopulations proceeds in response to specific chemotactic clues produced by tissue resident cells and is further amplified by incoming leukocytes. Over the last decade a number of receptors for chemokines and other chemoattractants have been identified on distinct leukocyte subpopulations participating to the pathogenesis of allergic inflammation. Preferential expression of discrete chemoattractant receptors on relevant cell types and their up-regulation in affected organs and animal models of allergic inflammation has helped to restrict the list of culprits. Although searching of the appropriate target for pharmacological intervention is still in progress, discrete chemoattractant receptors are already attracting a strong interest from the pharmaceutical industry. Here, we will review the most recent advances on the role that specific chemoattractant receptors play in the pathogenesis of allergic inflammation and will discuss emerging developments in this field.

Innate and adaptive immune responses evolve as protective mechanisms against infectious microorganisms in humans. CD14 and tolllike receptors (TLRs) are examples of pattern recognition receptors that detect antigenic molecules on the surface of gram-positive (peptidoglycans, lipoteichoic acid) and gram-negative (lipopolysaccharide) bacteria. In vitro studies suggest that lipopolysaccharide is a potent inducer of interleukin-12 production that is mediated by both CD14 and TLR4. The associated increase in interferon-γ steers our immune system away form the allergy-driven type-2 helper T cell phenotype. Epidemiological studies that shed light on the possible protective influences of natural microbial exposure on asthma and atopy development will be discussed. Recent insights into the complex mechanisms of human innate immunity suggest that genetic variability in genes encoding its components may alter the susceptibility to develop atopic disorders and other complex human diseases. The findings of these genetic association studies will be presented. Although highly conserved across a wide range of species, innate immunity genes demonstrate considerable inter-ethnic variability predominantly in the form of single nucleotide polymorphisms. The frequencies of these polymorphisms in CD14 and TLR genes in different ethnic groups will be discussed. Genetic variation in these genes may also play a role in the development of other human diseases that have an inflammatory component. Lastly, the prospect of using immunomodulatory agents targeting on the innate immunity to treat or even prevent asthma and other allergic diseases will be discussed.

Airway remodeling is a major change responsible for irreversible asthmatic airflow restriction. The Th-2 cytokines-dominant eosinophilic inflammatory mechanism cannot fully explain the progressive subepithelial fibrosis and structural changes in the extracellular matrix (ECM). Matrix metalloproteinases (MMPs) are the key enzymes responsible for ECM degradation. MMPs are normally produced and secreted under the tight regulation of, at least, 3 different levels: the gene transcriptional level, the activation of the latent form of enzyme, and the inactivation by specific endogenous inhibitors. In asthmatic condition, as shown by the large amount of accumulated evidence in this review, MMP-9 is the most relevant among the 23 kinds of human MMPs at present detected. Although the mechanism is still under investigation and not accurately known, the imbalance between MMP-9 and tissue inhibitor of metalloproteinase-1 is considered a major theory to explain the progression of asthmatic airway remodeling. Various inflammatory cytokines including TGF beta and growth factors play a pivotal role in MMP-9 production and secretion. This review mainly focuses upon the pivotal role of MMP-9 in airway remodeling, and also upon major cellular source of MMP-9 in asthma such as eosinophils, neutrophils, epithelial cells and alveolar macrophages. This review also refers to the partial contribution of nitric oxide to MMP-9 in asthma.

It has been hypothesized that T cell recognition of a self-antigen in the periphery, can lead to autoimmunity by activating T cells through T cell receptor signaling. However, in order for optimal activation to occur a second signal, termed “costimulation”, has to be delivered by antigen presenting cells to the T cells. Both the T cell receptor and co-stimulatory signals have been specific targets for therapeutic intervention in autoimmune disease. Strategies targeting both the T cell receptor and costimulation will be discussed in detail within the contents of these review articles (Burrows, Miller, and Vandenbark, for targeting TCR-dependent mechanisms; Weinberg and Miller targeting costimulatory molecules). In human autoimmune diseases, such as MS, RA, and inflammatory bowel disease, activated T cells are found within the inflammatory lesions. However, there has been no direct link between an “autoAg” and a specific T cell receptor that is responsible for the development and/or progression for most of these human diseases. Therefore, finding ways to target and suppress T cellspecific immune activation through mechanisms other than blocking, T cell recognition of autoAg will be discussed in 3 of the 6 reviews (Weinberg, Miller, and Bebo). It has long been noted that for several human autoimmune disorders (e.g. RA, SLE, and MS), there is a large increase of female to male cases. In MS and SLE, the ratio is 10:1 female to male. Thus, sex hormones may influence Ag-specific T cell function during and/or after recognition of autoAg. It has also been noted that female patients with relapsing autoimmune disease have far fewer clinical episodes during pregnancy, again suggesting that sex hormones or pregnancy-specific proteins may suppress T cell specific autoimmune responses. Therefore, modulating sex hormones and the use of pregnancy specific proteins/hormones may have important therapeutic implications for future treatment of autoimmune disease. This subject will be reviewed in the article by Bebo. The group of scientists that have been assembled to write these reviews have all worked with the autoimmune model experimental autoimmune encephalomyelitis (EAE), which is an animal model that mimics the clinical signs of MS. Therefore, the majority of these reviews will focus on discoveries made in the EAE model. Immunizing mice with myelin proteins in a strong immune adjuvant induces EAE, and the majority of autoAg specific T cell responses that have been studied to date are CD4 T cell responses. However, activated CD8 T cells are present in the spinal cord and brain lesions of multiple sclerosis patients, therefore, the final chapter of this issue will be devoted to autoantigen recognition of CD8 T cells and their destructive capabilities in autoimmune disease (Goverman).

Human autoimmune disease involves local activation of antigen-specific CD4+ T cells that produce inflammatory Th1 cytokines leading to the further recruitment and activation of lymphocytes and monocytes, resulting ultimately in the destruction of target tissue. Antigen presenting cells (APCs) initiate activation of CD4+ T cells in a multistep process that minimally involves co-ligation of the TCR and CD4 by the MHC class II / peptide complex and costimulation through additional T cell surface molecules such as CD28. Disruption of this highly orchestrated series of events can result in the direct modulation of CD4+ T cell behavior. The interaction between MHC and TCR holds unique promise as a focal point for therapeutic intervention in the pathology of CD4+ T cell-mediated diseases, and MHC class II-derived Recombinant TCR Ligands (“RTLs”) have emerged as a new class of therapeutics with potent clinical efficacy in a diverse set of animal models for multiple sclerosis. Here I review the systemic effect that RTL therapy has on the intact immune system and present an overview of a molecular mechanism by which RTL therapy could induce these systemic changes.

Certain members of the TNF-receptor family have shown proinflammatory function during immune activation and can be directly involved with the pathogenic effects observed during an autoimmune episode. The TNF-R family members summarized in this review includes: TNF-RI + II, OX40, and 4-1BB and they are expressed on a variety of leukocytes within the body. Studies within the last decade suggest that all of these proteins or their natural ligands can be targeted with various agents designed to diminish clinical signs of disease in autoimmune models. The data from the preclinical models specifically involving TNF-blockade have led to the development of clinical trials for patients with multiple sclerosis and rheumatoid arthritis. This review will chronicle the preclinical development of agents designed to inhibit OX40 and 4- 1BB functions in autoimmunity and discuss relevant preclinical and clinical data associated with TNF-blockade.

Autoimmune diseases are initiated and maintained by presentation of self antigen through complex interactions between different cells of the immune system. In most autoimmune disorders, autoantigen-specific responses are induced by the activation of specific T cells with self peptides displayed on activated antigen presenting cells (APCs). These T cells may then activate and drive B cell responses that either initiate or contribute to chronic disease pathogenesis. In order to activate the T cell, two signals are required: T cell receptor (TCR) engagement by autoantigen presented in the context of self MHC class II and costimulation (CD28-CD80 / CD86 interactions). Feedback must also be provided to the APC through MHC class II engagement by the TCR and through costimulatory events controlling T cell differentiation and effector function (CD154-CD40 interactions, among others). With this in mind, numerous strategies have been developed to block the engagement and activation of self-reactive cells. We review and discuss recent progress in understanding the efficacy and underlying molecular mechanisms of three separate immunotherapeutic strategies targeting the TCR and costimulatory molecules: i) blocking TCR signaling (using non-mitogenic anti-CD3 monoclonal antibody); ii) blocking CD28 costimulation (anti-B7 monoclonal antibody blockade); and iii) blocking CD40 engagement on APCs (anti-CD154 monoclonal antibody blockade).

Vaccination with self peptides contained within T cell receptor (TCR) chains, expressed by pathogenic Th1 cells can induce a second set of regulatory T cells that can reverse paralysis in rodents with experimental encephalomyelitis, and similarly, may have the potential to regulate myelin-reactive Th1 cells in patients with multiple sclerosis (MS). In this review, we discuss our recent discovery that TCR-reactive T cells generally possess classical inhibitory activity associated with Treg cells. CD4+CD25+ TCR-reactive T cells can inhibit CD4+CD25- indicator cells stimulated with anti-CD3 / anti-CD28 antibody in a dose-dependent and cell-contact-dependent manner. Additionally, CD4+CD25+ T cells from blood of healthy control donors have significant responses to a pool of discriminatory TCR peptides, including BV10S1P, BV19S20, BV13S7, BV12S2A2T, BV11S1A1T, BV21S3A1T, AV15S1, and BV12S1A1N1. Patients with MS have varying degrees of deficient responses to TCR peptides, and by association, a defect in Treg cell function as well. TCR peptide vaccination using a new tripeptide mixture emulsified in IFA produced strong T cell responses in 100% of MS recipients, a dramatic improvement over previous vaccines given i.d. in saline that induced TCR-reactive T cell responses in about 50% of recipients. Responders to vaccination had a tendency towards reduced MRI lesions, and an early indication of enhanced Treg activity mediated by TCR-reactive T cells that could provide suppression of target as well as bystander T cells. These data provide a strong foundation for future TCR vaccination studies that will critically test the ability of the tripeptide mixture to induce significantly enhanced Treg activity and possible clinical and MRI benefits in vivo.

The capacity of the pregnancy state to regulate T-cell function is well documented. A consequence of this regulation is that many Tcell mediated autoimmune disorders, including multiple sclerosis (MS) are suppressed during pregnancy. The suppression of MS during pregnancy is more potent than the currently available treatments for this disease. Thus, the study of immunoregulatory factors of pregnancy could potentially result in the discovery of novel MS treatments. The regulation of T-cell function during pregnancy is likely the result of significant hormonal changes and may well involve immunoregulatory proteins derived from the placenta. Pregnancy specific glycoproteins (PSGs) are the most abundant placentally derived glycoproteins in the maternal serum. The levels of PSGs are highest during the third trimester of pregnancy, a time marked by the most profound suppression of MS disease attacks. Recent studies by our laboratories, and others, suggest that PSGs regulate T-cell function. We propose this regulation occurs by two distinct, but complementary mechanisms. PSGs may regulate T-cell function by (1) directly signaling tetraspanins present on the cell surface and by (2) regulating T-cell function indirectly through signaling of tetraspanins expressed by macrophages and dendritic cells. In this report, we will review evidence implicating PSGs as important immunoregulatory proteins and discuss our recent findings regarding the mechanisms by which PSGs regulate T-cell function.

The role of CD8+ T cells in multiple sclerosis (MS) and its animal models has been enigmatic. Most studies of MS have focused on the role of CD4+ Th1 T cells and many therapeutic strategies have been directed toward ameliorating the activity of this subset. Some of these strategies were effective in experimental autoimmune encephalomyelitis (EAE), a widely used animal model for MS dependent on CD4+ T cells, but paradoxically have worsened disease in MS patients. A great deal of evidence suggests that CD8+ T cells contribute to the pathogenesis of MS and should be considered in designing therapies. CD8+ T cells outnumber CD4+ T cells in MS lesions, and both clonal expansion and enrichment of memory cells is preferentially seen in the CD8+ T cell subset in the brain and cerebrospinal fluid of MS patients. New animal models have been developed that employ myelin-specific CD8+ T cells to induce central nervous system autoimmunity. In a CD8+ T cell model targeting myelin basic protein, clinical signs and pathology distinct from CD4+ T cell-mediated disease were observed that exhibited similarities to some aspects of MS. These differences are consistent with distinct effector mechanisms employed by CD8+ and CD4+ T cells in mediating tissue damage and suggest a need to consider the activity of CD8+ T cells in drug design. This review will focus on our current understanding of the role of CD8+ T cells in MS and the new animal models that allow us to investigate further the pathogenicity of this subset.

Alzheimer's disease, the most common neurodegenerative dementia in the elderly, affects cognition, behavior and functioning, and a prominent neuroinflammatory component likely contributes to disease pathogenesis. The epidemiology of AD has previously shown that NSAID use decreases the incidence of AD, and evidence from tissue culture, in vivo models, and Alzheimer brain tissue studies indicate that inflammation in AD is mediated by the production of proinflammatory molecules, leading to microglial activation and neuronal damage. Preliminary clinical drug trials of anti-inflammatory agents, such as indomethacin, suggest slowing of cognitive decline in AD, further supporting a role for inflammation. The basic mechanisms underlying the AD neuroinflammatory cascade, which might accelerate the development of AD neuropathology, are poorly understood, but several recent studies implicate a number of established signaling pathways in this process. Microglial activation might involve beta-amyloid binding and activation of cell surface immune and adhesion molecules such as CD45, CD40, CD36 and integrins, with the subsequent recruitment of Src family tyrosine kinases such as Fyn, Lyn and Syk kinases. ERK and MAPK pathways are then activated, which induces proinflammatory gene expression and leads to the production of cytokines and chemokines. These molecules may then contribute to synaptic pruning, damage and loss, while TNFα can induce neuronal apoptosis and injury. The production of interleukins and other cytokines and chemokines also may lead to microglial activation, astrogliosis, and further secretion of proinflammatory molecules and amyloid, thus perpetuating the cascade. Simultaneously, direct neuronal injury from amyloid-induced signaling also contributes to neurodegeneration. Of clinical relevance, components of these pathways may be suitable targets for therapeutic modulation in AD and for the development of novel disease-modifying anti-inflammatory therapy.

Inflammation plays a variable part in the pathogenesis of several spinal disorders. Ankylosing spondylitis is a chronic inflammatory arthropathy of the spine and rheumatoid arthritis, whilst affecting predominantly limb joints, also affects the cervical spine in a significant proportion of people. Inflammation is also involved in disorders such as disc herniation and sciatica, which have previously been thought of as being primarily mechanical or degenerative. Anti-inflammatory agents which have been shown to be effective elsewhere in the body are discussed in this review as possible therapeutic agents in the spine. As the inflammatory cascade and immunopathology of these conditions continue to be elucidated, it has become apparent that individual molecules may be potential targets for inactivation or down-regulation. Candidates include pro-inflammatory cytokines, such as TNF-α, cytokines, e.g. IL-1 and IL-15, or enzymes enhancing the inflammation pathway such as the cyclooxygenases. Hence treatments based on inactivation of these molecules by various mechanisms, including antibodies, receptor antagonists, enzyme inhibitors or gene therapy, are being introduced. However, the mode of action of a particular molecule can be complex and sometimes apparently contradictory. For example, TNF-α is known to play an important role in promoting inflammation by upregulating expression of cell adhesion molecules on endothelial cells and stimulating the production of reactive oxygen intermediates, nitric oxide and prostaglandins. However, it can also have an immunosuppressive and anti-inflammatory role after prolonged release. Therefore, although inhibitors of many of these molecules are now in clinical application and trials (many with promising results in rheumatoid arthritis), it is important to remain vigilant and monitor long-term outcomes particularly when these treatments are used in clinical syndromes with relatively poorly defined immunopathology such as spinal disorders.

The increasing levels of morbidity and mortality due to the rising prevalence of asthma and other allergic diseases have inspired investigations of several new molecular techniques to improve treatment. Recently, several preclinical studies have been published which utilize attributes or facets of DNA to address asthma therapy. These novel therapeutics include antisense oligonucleotides against TH2 cytokines and associated transcription factors. While no clinical experience has yet been reported for any of these areas of research in asthma, specific small molecule inhibitors of TH2 cell responses would be desirable for treatment of this chronic disease. Six transcription factors (c- Maf, NF-AT, NF-IL-6, AP-1, STAT-6 and GATA-3) have been implicated in the differentiation of TH2-type lymphocytes and therefore, in addition to TH2-type cytokines, represent therapeutic targets for asthma. This review will focus on new research involving suppression of Th2-type cytokines and associated transcription factors using antisense and decoy oligonucleotides. Recently, novel oligonucleotides have been devised to improve stability in vitro and in vivo stability against nucleases, and the efficacy of these approaches will also be presented.