Current Drug Targets - Inflammation & Allergy - Volume 4, Issue 3, 2005

Both acute and chronic inflammatory responses are common features of a variety of pathological conditions. Likewise, allergic inflammation is an important reaction in ailments such as asthma and atopic dermatitis. In all of these conditions, the severity and fidelity of the inflammatory response is dependent on the recruitment of activated inflammatory cells into inflamed sites and on cellular communication. Although this is often achieved through direct cell-to-cell adhesion via specific intercellular adhesion molecules, cells also signal one another using soluble mediators, such as cytokines and chemokines. Moreover, one population of cells may respond directly to a specific stimulus by elaborating a particular cytokine to exert effects on a yet another population of cells; for example, inflammatory effector cells (monocytes and neutrophils) may be locally recruited and activated in response to specific chemotactic signals, resulting in further amplification of a cytokine cascade. Non-immune cells, such as endothelial and epithelial cells and other stromal cells, also play key roles in the generation, maintenance and resolution of both local and systemic inflammatory responses. The thirteen articles in this special issue, entitled “The kinetics and profiles of inflammatory cells during inflammatory and allergic responses,” address the biology and function of various cell populations under both normal and pathophysiological conditions. First discussed are the inflammatory effector cells, including polymorphonuclear neutrophils, which act as a first line of defense, and macrophages, which participate in inflammatory and immunological responses (Chapters 1 and 2). In Chapters 3 and 4, the involvement of T cells in such autoimmune diseases as rheumatoid arthritis and systemic lupus erythematosus is discussed. Recent advances in our understanding of the roles played by cytokines and chemokines during pulmonary diseases are presented in Chapters 5 and 7, while the role of bronchial epithelial cells in allergic reactions is discussed in Chapter 6. The importance of endothelial cells in both angiogenesis and inflammation is now well recognized. Chapter 8 summarizes the most relevant information on adhesion molecules and anti-adhesive and anti-angiogenic agents. In Chapter 9, the authors review recent findings on the role of osteoclasts and osteoblasts in bone remodeling under normal conditions and such pathophysiological conditions as rheumatoid arthritis. Dysregulation of inflammatory mediators or their receptors in keratinocytes during the evolution of chronic inflammatory skin diseases is discussed in Chapter 10. In Chapter 11, the authors review recent findings indicating that the reciprocal interaction of activated glial cells, COX enzymes and prostaglandins mediate both neurodegeneration and neuroprotection during brain inflammation. Finally, the crucial role played by renal mesangial and epithelial cells in the glomerular injury and inflammation seen in such ailments as glomerulonephritis are discussed in Chapters 12 and 13. I hope that this special issue sheds light on all the major cell populations involved in acute and chronic inflammation and in aberrant immune responses. Our increased understanding of the roles of specific cell types, cell surface molecules and their products at inflamed sites may provide the basis for new approaches to therapeutic immunointervention in disease processes. More broadly, it should contribute to our understanding of the pathobiological mechanisms of a variety of diseases affecting every organ system.

Polymorphonuclear neutrophils (PMNs) are usually thought of as the leukocyte population involved in acute inflammatory responses, acting as a first line of defense against invading microorganisms. These terminally differentiated cells are generally not thought of as an important source of de novo synthesis of polypeptide mediators. Recent progress has shown, however, that PMNs are able to synthesize cytokines in response to a variety of inflammatory stimuli and during certain pathological conditions. The expression profiles of PMN-derived cytokines are similar with those of monocytes/macrophages, major professional phagocytes. Like monocytes, PMNs are able to secrete proinflammatory cytokines [e.g., tumor necrosis factor (TNF)-α and interleukin (IL)-1β], both CC and CXC chemokines [e.g., IL-8, interferoninducible protein 10 (IP-10) and macrophage inflammatory protein (MIP)-1α], and angiogenic factors [e.g., vascular endothelial growth factor (VEGF)]. The secretion of cytokines by activated PMNs is regulated by immunoregulatory cytokines such as interferon (IFN)-γ, IL-4, IL-10 and IL-13. In addition to acute inflammatory responses, PMNs and PMN-derived cytokines appear to be involved in the pathogenesis of such chronic inflammatory disorders as rheumatoid arthritis, inflammatory bowel diseases and mycobacterial infections. Conceivably, these findings place PMNs at a pivotal position where they regulate and orchestrate not only acute inflammatory responses but also chronic inflammation and immune regulation. As such, inhibition of PMN-derived cytokines is viewed as a potentially useful strategy for therapeutic immunointervention.

The inflammatory process is usually tightly regulated, involving both signals that initiate and maintain inflammation and signals that shut the process down. An imbalance between the two signals leaves inflammation unchecked, resulting in cellular and tissue damage. Macrophages are a major component of the mononuclear phagocyte system that consists of closely related cells of bone marrow origin, including blood monocytes, and tissue macrophages. From the blood, monocytes migrate into various tissues and transform macrophages. In inflammation, macrophages have three major function; antigen presentation, phagocytosis, and immunomodulation through production of various cytokines and growth factors. Macrophages play a critical role in the initiation, maintenance, and resolution of inflammation. They are activated and deactivated in the inflammatory process. Activation signals include cytokines (interferon γ, granulocyte-monocyte colony stimulating factor, and tumor necrosis factor α), bacterial lipopolysaccharide, extracellular matrix proteins, and other chemical mediators. Inhibition of inflammation by removal or deactivation of mediators and inflammatory effector cells permits the host to repair damages tissues. Activated macrophages are deactivated by anti-inflammatory cytokines (interleukin 10 and transforming growth factor ß) and cytokine antagonists that are mainly produced by macrophages. Macrophages participate in the autoregulatory loop in the inflammatory process. Because macrophages produce a wide range of biologically active molecules participated in both beneficial and detrimental outcomes in inflammation, therapeutic interventions targeted macrophages and their products may open new avenues for controlling inflammatory diseases.

Immune and inflammatory responses are governed by antigen-specific T cells, whose activation, differentiation and effector function are induced by signals delivered via the T cell antigen receptor (TCR) and by costimulatory and cytokine receptors. The molecular events leading to the activation of naïve T cells have been extensively studied and are well characterized. Much less is known about the molecular and biochemical events regulating the activation of T cells in chronic inflammatory diseases such as rheumatoid arthritis (RA). This review examines the current state of knowledge of T cell activation in chronic inflammation, focusing on RA, and summarizes experimental data which indicate that the chronic inflammatory process may profoundly affect TCR and cytokine signal transduction pathways. We present evidence suggesting that in chronic inflammation, the antigen-driven TCR-mediated processes are attenuated, while cytokine-driven effector responses are sustained or even enhanced. The possible implications of this inbalance are discussed.

It is widely accepted that T cells with defective function play a central role in the pathogenesis of systemic lupus erythematosus (SLE). The detailed molecular mechanism underlying the aberrant function of SLE T cells is now being revealed. The TCR zeta chain, transcription factor, elf-1, inflammation signal transducer NF-kB, and PKC theta have been identified as the responsible molecules. In contrast to the defective signal transduction molecules, surface structures such as adhesion molecules, and co-stimulators have been reported to increase in their expression and function. Glucocorticoids and immunosuppressive agents have greatly improved the outcome of acute diseases and 5-year survival rate. However, it is suggested that long-term survival and quality of life appears to be unsatisfactory. Although the medical management of SLE is not sufficient to warrant long-term survival of young patients, recent progress in anti-cytokine biologics therapy against rheumatoid arthritis (RA) has facilitated searching for the molecular targets of SLE. In this report, we briefly review the molecular basis of SLE pathogenesis, and discuss possible therapeutic targets in this disease, focusing particularly on signal transduction and adhesion molecules in T cells.

The mortality of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) remain high despite advances in our knowledge and intensive care. This supports the contention that we need to further our understanding of the mediators that are involved in the pathogenesis of ARDS. The pathogenesis of ARDS proceeds as a continuum from exudation and inflammation to a fibroproliferative phase of diffuse alveolar damage. While a number of mediators are involved in the pathogenesis of ARDS, members of the CXC chemokine family have been determined to play a critical and pleiotropic role in promoting both recruitment of inflammatory cells, as well as in mediating aberrant vascular remodeling during both phases of ARDS. The importance of the biology of CXC chemokines in ALI/ARDS will be discussed in this review.

Bronchial epithelial cells (BEC) are known to play an integral role in the airway defense mechanism via mucociliary system as well as mechanical barriers. Recent studies further indicate that BEC produce and release biologically active compounds including lipid mediators, growth factors, endothelin and a variety of cytokines/chemokines important in the pathogenesis of airway disorders. Cytokines and chemokines produced by BEC include IL-6, IL-8, G-CSF, GM-CSF, RANTES, eotaxin and TARC. Pro-inflammatory cytokines IL-1 and TNF-α, generally upregulate expression and release these cytokines/chemokines. BEC from patients with bronchial asthma showed increased levels of mRNA for these potent inflammatory peptides. BEC also interact with immune and inflammatory cells by direct adhesion as well as by humoral factors including cytokines. For example, eosinophil adhesion to BEC may be an important signal for the activation and degranulation of eosinophils. BEC is also believed to take part in the airway mucosal immunity via Toll-like receptors. Finally, BEC may play a crucial role in the processes of airway remodeling by cross-talk with mesenchymal cells. These findings strongly suggest that BEC are actively involved as regulators of allergic inflammatory responses, and become a target for therapeutic intervention.

The incidence of asthma has continued to rise worldwide with the number of severe asthmatic episodes dramatically increasing especially in children. Over the past several years researchers have realized that by controlling the influx of inflammatory cells that damage the airway and perpetuate the chronic responses, asthmatic disease can be attenuated. The modulation of the immune/inflammatory response has been primarily managed by use of inhaled and/or oral steroids. However, more specific therapy focused on inflammatory cell influx is desired to target the appropriate cell populations and alleviate specific aspects of disease without non-specific side effects. The chemokine family of cytokines control recruitment of leukocyte populations through specific receptors that are differentially expressed by certain cellular populations in various immune environments. Defining the type of receptors that are displayed by key cell populations involved in asthmatic responses has been the focus of many academic and pharmaceutic programs. This review will highlight the various areas that have been identified and those that appear to provide a future for therapeutic intervention.

Endothelial cells are involved in leukocyte extravasation underlying inflammation. A number of adhesion molecules play a role in leukocyte-endothelial interactions. New vessel formation, termed angiogenesis, is also crucial for leukocyte extravasation. The outcome of neovascularization is highly dependent on the balance or imbalance between angiogenic mediators and inhibitors. There have been several attempts to therapeutically interfere with the cellular and molecular mechanisms, such as leukocyte-endothelial cell adhesion and angiogenesis. Most studies have been performed using animal models of various types of inflammation, such as arthritis. In addition, a very limited number of human clinical trials gave promising results. In this review, authors summarize the most relevant information on adhesion molecules, as well as angiogenic and angiostatic agents. In addition, further perspectives of anti-adhesive and anti-angiogenic therapy are also discussed. Specific targeting of pathological endothelial function including adhesion and angiogenesis, may be useful for the future management of various inflammatory diseases.

Bone homeostasis is maintained by a balance between bone resorption by osteoclasts and bone formation by osteoblasts. Osteoblasts not only play a central role in bone formation by synthesizing multiple bone matrix proteins, but regulate osteoclast maturation by soluble factors and cognate interaction, resulting in bone resorption. Osteoclast maturation requires stimulation by RANKL expressed on osteoblasts, and the cognate interaction is mediated by firm adhesion via ICAM-1. During the processes, pro-inflammatory cytokines such as IL- 1 and TNF-α, cause an imbalance in bone metabolism, by favoring bone resorption via the induction of RANKL and ICAM-1 on osteoblasts. These inflammatory signals originate from the immune system, the largest source of cell-derived regulatory signals, and such immunological signals to the bone are transmitted primarily via osteoblasts to induce osteoclast maturation, resulting in secondary osteoporosis. Actually, such phenomena mainly occur at the interface between proliferating synovium and bone tissue in rheumatoid arthritis (RA). Thus, therapeutic strategies for these conditions, an anti-TNF- α antibody and an IL-1 receptor antagonist, effective for treating RA disease activity, also reduce secondary osteoporosis and joint destruction. Based on an improved understanding of immune signals, investigation of the suppression of cell functions may lead to improved understanding and better treatment of diseases of bone metabolism and osteoporosis.

Although in the past, keratinocytes were considered simply as passive targets of immunological attack from infiltrating T lymphocytes, a number of studies have definitively demonstrated that keratinocytes actively participate in the cutaneous immune responses. Upon activation, keratinocytes express a plethora of cytokines, chemokines and accessory molecules, which can transmit both positive and negative signals to cells of innate and adaptive immunity. Dysregulation and abnormal expression of inflammatory mediators or their receptors in keratinocytes are relevant to the pathogenesis of chronic inflammatory skin diseases such as psoriasis, atopic dermatitis and allergic contact dermatitis.

Many brain disorders such as Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis (ALS), Huntington, stroke, head trauma, and infection, are associated with inflammation that is involved in neuropathologenesis and hyperalgesis. Microglia and astrocytes act as immune cells in the inflamed brain. Both cell types, but especially microglia, are thought to contribute to the onset of inflammation in many brain diseases by producing deleterious proinflammatory mediators. Prostaglandins (PGs), which are critical mediators of physiologic processes and inflammation, are largely produced by activated microglia and reactive astrocytes during brain inflammation. These compounds are converted from arachnoidic acid (AA) by two isoforms of the cyclooxygenase (COX) enzyme, namely COX-1 and COX-2. In particular, the action of COX-2 and PGs in CNS inflammation has gained much attention recently. PGs have been found to act neuroprotectively by elevating intracellular cAMP levels in neurons. These molecules also function as anti-inflammatory molecules to reduce the production of nitric oxide and proinflammatory cytokines, and to increase the expression of anti-inflammatory cytokines. However, accumulating evidence also shows that COX inhibitors alleviate various types of brain damage via suppressing inflammatory reactions. Accordingly, the roles of two COX enzymes in mediating inflammation and anti-inflammation have recently been debated. We provide here a review of recent findings indicating that the reciprocal interaction of glial cell activation, COX enzymes and PGs mediates neurodegeneration and neuroprotection during brain inflammation. In addition, the mechanism by which PGs mediate signaling is discussed.

The mesangium occupies a central anatomical position in the glomerulus, and also plays an important regulatory role in immunemediated glomerular diseases, with an active participation in the response to local inflammation. In general, the mesangial cell responses to the pathological stimuli are associated with the main events of glomerular injury: leukocyte infiltration, cell proliferation and fibrosis. Leukocyte migration and infiltration into the glomerulus is responsible for the initiation and amplification of glomerular injury, and is mediated by adhesion molecules and chemokines, which can be locally synthesized by mesangial cells. The increase in mesangial cell number is also due to proliferation of intrinsic mesangial cell population. Regulatory mechanisms of mesangial cell replication include a complex array of factors which control cell proliferation, survival and apoptosis. Mesangial matrix accumulation leading to glomerulosclerosis, is a consequence of an imbalance between matrix production and degradation, and is controlled by growth factors and pro-inflammatory cytokines. The initial phase of immune-mediated glomerular inflammation depends on the interaction of immune complexes with specific Fc receptors in infiltrating leukocytes and resident mesangial cells, the ability of immune complexes to activate complement system, and on local inflammatory processes. Activated mesangial cells then produce many inflammatory mediators leading to amplification of the injury. This review will focus on the biological functions of mesangial cells that contribute to glomerular injury, with special attention to immune-mediated glomerulonephritis. Furthermore, new therapies based on the pathophysiology of the mesangial cell that are being developed in experimental models are also proposed.

Each year, worldwide, there is an increasing number of patients with chronic kidney disease that progress to end-stage renal disease. Glomerulonephritis (GN) is the commonest single cause of end-stage renal failure in the world [1]. GN can be a manifestation of primary renal injury or may be a secondary feature of a systemic disease process, for example Systemic Lupus Erythematosus (SLE) and Anti-Neutrophilic Cytoplasmic Antibody (ANCA) associated vasculitis. Understanding of the immunopathogenesis of GN has advanced considerably over the last 25 years, particularly the immune system's role. The injurious role of infiltrating leukocytes and humoral mediators has been emphasised, however, the contribution of intrinsic renal cells has proved difficult to define. Most evidence for the pro-inflammatory capacity of intrinsic renal cells has been derived from in vitro studies. Although cytokine production by intrinsic renal cells has been demonstrated by immunohistochemistry and in situ hybridisation studies in renal tissue during the development of GN, the functional contribution of this cytokine production to renal injury was unknown. Little was known about direct and specific interactions between different glomerular cell types and infiltrating leukocytes in the pathogenesis of GN. The development of mice with genetic deficiencies of pro-inflammatory mediators and cytokines, and the technique of bone marrow transplantation into irradiated recipients to produce chimeric mice with restricted cytokine expression has allowed in vivo assessment of the functional contribution made by intrinsic renal cells. Studies have demonstrated the significant contribution of intrinsic renal cell derived cytokines (e.g. TNF) in mediating GN, whereas others (IL-1α) have a relatively minor role.

The matrix metalloproteinases (MMPs) comprise a family of enzymes that collectively can degrade all components of the extracellular matrix (ECM). MMPs play an important role in many physiological processes such as embryonic development and growth, tissue remodelling and repair. Overexpression and activation of MMPs contributes to many pathologies, including arthritis, cardiovascular disease, tumour progression and lung disease. Targeted mutagenesis has allowed investigators to examine the contribution of MMPs to these physiological and pathologic processes. In this manuscript, we will present an up-to date review of these studies. Rheumatoid arthritis (RA) and osteoarthritis (OA) are chronic diseases that result in cartilage degradation and loss of joint function. MMPs have been implicated in the collagen breakdown that contributes to joint destruction. Current available drugs to treat arthritis are predominantly directed towards the control of pain and/or the inflammation associated with joint synovitis but they do little to reduce joint destruction. Synthetic MMP inhibitors have been developed and in animal models of OA and/or RA, these agents have shown chondroprotective effects. However, results from clinical trials in RA have been equivocal, with some studies being terminated because of lack of efficacy or safety concerns. Increased understanding of the structure, regulation and function of individual MMPs may lead to more effective strategies. Approaches aimed at multiple steps of the pathogenesis of arthritis may be needed to break the chronic cycle of joint destruction. In the future, it will be important to have drugs that prevent the structural damage caused by bone and cartilage breakdown.

Dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) are metabolic intermediates in the production of potent androgens, estrogens and other less well-characterized steroids. DHEA(S)1 and closely related steroid hormones have a variety of immunological effects both in vitro and in vivo in experimental animals and humans. Many of these effects have been demonstrated in animal models where there is little circulating DHEA(S), and the demonstrated effects are generally seen at concentrations of DHEA(S) which are supraphysiological in man. The physiological role of DHEA(S) in the immunological system is unknown. Furthermore, the molecular mechanism of action of DHEA(S) is unclear. In this review, I focus on studies of the immunological effects of DHEA(S) and closely related steroid metabolites and analogs, mainly derived from literature published in the last five years. My purpose is to describe the demonstrated effects and to highlight some of the remaining major research issues in this field. These issues include defining the molecular mechanism of DHEA(S) action; determining whether the effect of DHEA(S) is related to the steroid itself or to a metabolic product of DHEA; determining the relationship of physiological function to the pharmacological effects; and determining the molecular basis for species-specific differences in effects.

Chemokines are small secreted proteins that chemoattract and activate immune and non-immune cells both in vivo and in vitro. Besides their well-established role in the immune system, several recent reports have suggested that chemokines and their receptors may also play a role in the central nervous system (CNS). The best-known central action is their ability to act as immuno-inflammatory mediators. Indeed, these proteins regulate the leukocyte infiltration in the brain during inflammatory and infectious diseases. However, recent studies clearly demonstrate that chemokines and their receptors are constitutively expressed by glial and neuronal cells in the CNS, where they are involved in intercellular communication. The goal of this review is to summarize recent information concerning the role of chemokines in brain functions. The first part will focus on the expression of chemokines and their receptors in the CNS with the main spotlight on the neuronal expression. In the second part, we will discuss the role of chemokines and their receptors in normal brain physiology. Because several chemokines are involved in neuroinflammatory and neurodegenerative disorders, the role of chemokines and their receptors in these diseases is reviewed further in this section. In conclusion, the implication of chemokines in cellular communication could allow: i) to identify a new pathway for neuron-neuron and/or glia-glia and/or neuron-glia communications that are relevant to both normal brain function and neuroinflammatory and neurodegenerative diseases; ii) to develop new therapeutic approaches for still untreatable diseases further.

Accidents evoked by venomous animals are common in tropical regions. In Brazil, envenomation evoked by snakes, spiders and scorpions are an important public health problem. Their venoms are composed of a great number of toxins, which are capable of acting on tissue and plasma components with consequent toxic and pharmacological effects. On the other hand, the diversity of venom composition makes them important source of toxins that can be employed as scientific tools. Here we describe the mechanisms of anti and pro-inflammatory properties of toxins of Bothrops and Crotalus genus snakes and Loxosceles and Phoneutria genus spider venoms. The emphasis was to summarise, both in vivo and in vitro, studies that focused on the action of phospholipases, metalloproteinases and sphingomyelinase D on vascular and cellular aspects of the process as well as the complex network of chemical mediators involved.