Autoimmune diseases are immune disorders characterized by T cell hyperactivity and B cell overstimulation leading to overproduction of autoantibodies. Although the pathogenesis of various autoimmune diseases remains to be elucidated, environmental factors have been thought to contribute to the initiation and maintenance of auto-respond inflammation. Toll-like receptors (TLRs) are pattern recognition receptors belonging to innate immunity that recognize and defend invading microorganisms. Besides these exogenous pathogen-associated molecular patterns, TLRs can also bind with damage-associated molecular patterns produced under strike or by tissue damage or cells apoptosis. It is believed that TLRs build a bridge between innate immunity and autoimmunity. There are five adaptors to TLRs including MyD88, TRIF, TIRAP/MAL, TRAM, and SARM. Upon activation, TLRs recruit specific adaptors to initiate the downstream signaling pathways leading to the production of inflammatory cytokines and chemokines. Under certain circumstances, ligation of TLRs drives to aberrant activation and unrestricted inflammatory responses, thereby contributing to the perpetuation of inflammation in autoimmune diseases. In the past, most studies focused on the intracellular TLRs, such as TLR3, TLR7, and TLR9, but recent studies reveal that cell surface TLRs, especially TLR2 and TLR4, also play an essential role in the development of autoimmune diseases and afford multiple therapeutic targets. In this review, we summarized the biological characteristics, signaling mechanisms of TLR2/4, the negative regulators of TLR2/4 pathway, and the pivotal function of TLR2/4 in the pathogenesis of autoimmune diseases including rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis, Sjogren’s syndrome, psoriasis, multiple sclerosis, and autoimmune diabetes.
Respiratory syncytial virus (RSV) is amongst the most important pathogenic infections of childhood and is associated with significant morbidity and mortality. Although there have been extensive studies of epidemiology, clinical manifestations, diagnostic techniques, animal models and the immunobiology of infection, there is not yet a convincing and safe vaccine available. The major histopathologic characteristics of RSV infection are acute bronchiolitis, mucosal and submucosal edema, and luminal occlusion by cellular debris of sloughed epithelial cells mixed with macrophages, strands of fibrin, and some mucin. There is a single RSV serotype with two major antigenic subgroups, A and B. Strains of both subtypes often co-circulate, but usually one subtype predominates. In temperate climates, RSV infections reflect a distinct seasonality with onset in late fall or early winter. It is believed that most children will experience at least one RSV infection by the age of 2 years. There are several key animal models of RSV. These include a model in mice and, more importantly, a bovine model; the latter reflects distinct similarity to the human disease. Importantly, the prevalence of asthma is significantly higher amongst children who are hospitalized with RSV in infancy or early childhood. However, there have been only limited investigations of candidate genes that have the potential to explain this increase in susceptibility. An atopic predisposition appears to predispose to subsequent development of asthma and it is likely that subsequent development of asthma is secondary to the pathogenic inflammatory response involving cytokines, chemokines and their cognate receptors. Numerous approaches to the development of RSV vaccines are being evaluated, as are the use of newer antiviral agents to mitigate disease. There is also significant attention being placed on the potential impact of co-infection and defining the natural history of RSV. Clearly, more research is required to define the relationships between RSV bronchiolitis, other viral induced inflammatory responses, and asthma.
Throughout the twentieth century, there were striking increases in the incidences of many chronic inflammatory disorders in the rich developed countries. These included autoimmune disorders such as Type 1 diabetes and multiple sclerosis. Although genetics and specific triggering mechanisms such as molecular mimicry and viruses are likely to be involved, the increases have been so rapid that any explanation that omits environmental change is incomplete. This chapter suggests that a series of environmental factors, most of them microbial, have led to a decrease in the efficiency of our immunoregulatory mechanisms because we are in a state of evolved dependence on organisms with which we co-evolved (and that had to be tolerated) as inducers of immunoregulatory circuits. These organisms (“Old Friends”) are depleted from the modern urban environment. Rather than considering fetal programming by maternal microbial exposures, neonatal programming, the hygiene hypothesis, gut microbiota, and diet as separate and competing hypotheses, I attempt here to integrate these ideas under a single umbrella concept that can provide the missing immunoregulatory environmental factor that is needed to explain the recent increases in autoimmune disease.
Atopic dermatitis (AD) is a chronic inflammatory skin disease with specific immune and inflammatory mechanisms. Atopy is among the major features of the diagnosis criteria for AD but is not an essential feature. Thus, patients diagnosed with AD can be atopic or non-atopic. This review focuses on the role of IgE, mast cells, and eosinophils in the pathogenesis of AD. The known functions of IgE in allergic inflammation suggest that IgE and IgE-mediated mast cell and eosinophil activation contribute to AD, but direct evidence supporting this is scarce. The level of IgE (thus the degree of allergic sensitization) is associated with severity of AD and contributed by abnormality of skin barrier, a key feature of AD. The function of IgE in development of AD is supported by the beneficial effect of anti-IgE therapy in a number of clinical studies. The role of mast cells in AD is suggested by the increase in the mast cell number and mast cell activation in AD lesions and the association between mast cell activation and AD. It is further suggested by their role in mouse models of AD as well as by the effect of therapeutic agents for AD that can affect mast cells. The role of eosinophils in AD is suggested by the presence of eosinophilia in AD patients and eosinophil infiltrates in AD lesions. It is further supported by information that links AD to cytokines and chemokines associated with production, recruitment, and activation of eosinophils.
Lately, vitamin D has been linked with metabolic and immunological processes, which established its role as an essential component of human health preservation. Vitamin D has been defined as natural immune modulators, and upon activation of its receptors (VDRs), it regulates calcium metabolism, cellular growth, proliferation and apoptosis, and other immunological functions. Epidemiological data underline a strong correlation between poor vitamin D status and higher risk for chronic inflammatory illnesses of various etiologies, including autoimmune diseases. Epidemiological, genetic, and basic studies indicated a potential role of vitamin D in the pathogenesis of certain systemic and organ-specific autoimmune diseases. These studies demonstrate correlation between low vitamin D and prevalence of diseases. In addition, VDRs’ polymorphisms observed in some of these autoimmune diseases may further support a plausible pathogenic link. Notably, for some autoimmune disease, no correlation with vitamin D levels could be confirmed. Thus, in the current review we present the body of evidence regarding the plausible roles of vitamin D and VDR’s polymorphism in the pathogenesis of autoimmunity. We summarize the data regarding systemic (i.e., systemic lupus erythematosus, rheumatoid arthritis, etc.) and organ-specific (i.e., multiple sclerosis, diabetes mellitus, primary biliary cirrhosis, etc.) autoimmune diseases, in which low level of vitamin D was found comparing to healthy subjects. In addition, we discuss the correlations between vitamin D levels and clinical manifestations and/or activity of diseases. In this context, we address the rational for vitamin D supplementation in patients suffering from autoimmune diseases. Further studies addressing the mechanisms by which vitamin D affects autoimmunity and the proper supplementation required are needed.
A variety of mechanisms have been suggested as the means by which infections can initiate and/or exacerbate autoimmune diseases. One mechanism is molecular mimicry, where a foreign antigen shares sequence or structural similarities with self-antigens. Molecular mimicry has typically been characterized on an antibody or T cell level. However, structural relatedness between pathogen and self does not account for T cell activation in a number of autoimmune diseases. A proposed mechanism that could have been misinterpreted for molecular mimicry is the expression of dual T cell receptors (TCR) on a single T cell. These T cells have dual reactivity to both foreign and self-antigens leaving the host vulnerable to foreign insults capable of triggering an autoimmune response. In this review, we briefly discuss what is known about molecular mimicry followed by a discussion of the current understanding of dual TCRs. Finally, we discuss three mechanisms, including molecular mimicry, dual TCRs, and chimeric TCRs, by which dual reactivity of the T cell may play a role in autoimmune diseases.
The “Bermuda triangle” of genetics, environment and autoimmunity is involved in the pathogenesis of rheumatoid arthritis (RA). Various aspects of genetic contribution to the etiology, pathogenesis and outcome of RA are discussed in this review. The heritability of RA has been estimated to be about 60 %, while the contribution of HLA to heritability has been estimated to be 11–37 %. Apart from known shared epitope (SE) alleles, such as HLA-DRB1*01 and DRB1*04, other HLA alleles, such as HLA-DRB1*13 and DRB1*15 have been linked to RA susceptibility. A novel SE classification divides SE alleles into S1, S2, S3P and S3D groups, where primarily S2 and S3P groups have been associated with predisposition to seropositive RA. The most relevant non-HLA gene single nucleotide polymorphisms (SNPs) associated with RA include PTPN22, IL23R, TRAF1, CTLA4, IRF5, STAT4, CCR6, PADI4. Large genome-wide association studies (GWAS) have identified more than 30 loci involved in RA pathogenesis. HLA and some non-HLA genes may differentiate between anti-citrullinated protein antibody (ACPA) seropositive and seronegative RA. Genetic susceptibility has also been associated with environmental factors, primarily smoking. Some GWAS studies carried out in rodent models of arthritis have confirmed the role of human genes. For example, in the collagen-induced (CIA) and proteoglycan-induced arthritis (PgIA) models, two important loci — Pgia26/Cia5 and Pgia2/Cia2/Cia3, corresponding the human PTPN22/CD2 and TRAF1/C5 loci, respectively — have been identified. Finally, pharmacogenomics identified SNPs or multiple genetic signatures that may be associated with responses to traditional disease-modifying drugs and biologics.
Quinine was first recognized as a potent antimalarial agent hundreds of years ago. Since then, the beneficial effects of quinine and its more advanced synthetic forms, chloroquine and hydroxychloroquine, have been increasingly recognized in a myriad of other diseases in addition to malaria. In recent years, antimalarials were shown to have various immunomodulatory effects, and currently have an established role in the management of rheumatic diseases, such as systemic lupus erythematosus and rheumatoid arthritis, skin diseases, and in the treatment of chronic Q fever. Lately, additional metabolic, cardiovascular, antithrombotic, and antineoplastic effects of antimalarials were shown. In this review, we discuss the known various immunomodulatory mechanisms of antimalarials and the current evidence for their beneficial effects in various diseases and in potential novel applications.
Historically, vitamin D has been associated with the regulation of bone metabolism. However, increasing evidence demonstrates a strong association between vitamin D signaling and many biological processes that regulate immune responses. The discovery of the vitamin D receptor in multiple immune cell lineages, such as monocytes, dendritic cells, and activated T cells credits vitamin D with a novel role in modulating immunological functions and its subsequent role in the development or prevention of autoimmune diseases. In this review we, discuss five major areas in vitamin D biology of high immunological significance: (1) the metabolism of vitamin D; (2) the significance of vitamin D receptor polymorphisms in autoimmune diseases, such as multiple sclerosis, type 1 diabetes mellitus, and systemic lupus erythematosus; (3) vitamin D receptor transcriptional regulation of immune cell lineages, including Th1, Th17, Th2, regulatory T, and natural killer T cells; (4) the prevalence of vitamin D insufficiency/deficiency in patients with multiple sclerosis, type 1 diabetes mellitus, and systemic lupus erythematosus; and finally, (5) the therapeutic effects of vitamin D supplementation on disease severity and progression.
Chronic granulomatous disease (CGD) was first described in the 1950s and has become a paradigm for genetic neutrophil diseases. It is characterized by recurrent infections with a narrow spectrum of bacteria and fungi as well as a common set of inflammatory complications most notably including inflammatory bowel disease. Over the last half century major advances in management have profoundly altered the major clinical issues and the life expectancy of CGD. With X-linked and autosomal recessive forms, it has been an important disease for the development of bone marrow transplantation and gene therapy. Some of the recent developments in infectious syndromes, inflammatory complications, and curative approaches are discussed in this review.
Over the last decade, the management of psoriasis has witnessed a paradigm shift. Thanks to the increasing knowledge about the pathogenesis of psoriasis, targeted treatments with monoclonal antibodies have been developed. These antibodies, which target the pathogenic TNF/IL-23/IL-17-pathway, were shown to be safe and efficacious in the management of most patients with moderate to severe chronic plaque psoriasis. Recently, molecular and genetic studies in pustular and erythrodermic psoriasis have identified additional inflammatory pathways, providing evidence that psoriasis is a heterogeneous disease and highlighting the requirement for personalized disease characterization for treatment optimization. In this article, we will review these advances and provide an update on the currently available treatment arsenal. We discuss the efficacy and safety profile of these individual therapeutic agents and describe their use in special indications. We will also describe the current understanding of psoriasis as a systemic disease associated with multiple comorbidities and illustrate its impact in the management of psoriatic patients. Finally, we discuss ongoing therapeutic developments as well as unmet needs and future perspectives in the field of psoriasis.
Globally, the rising consumption of fish and its derivatives, due to its nutritional value and divergence of international cuisines, has led to an increase in reports of adverse reactions to fish. Reactions to fish are not only mediated by the immune system causing allergies, but are often caused by various toxins and parasites including ciguatera and Anisakis. Allergic reactions to fish can be serious and life threatening and children usually do not outgrow this type of food allergy. The route of exposure is not only restricted to ingestion but include manual handling and inhalation of cooking vapors in the domestic and occupational environment. Prevalence rates of self-reported fish allergy range from 0.2 to 2.29 % in the general population, but can reach up to 8 % among fish processing workers. Fish allergy seems to vary with geographical eating habits, type of fish processing, and fish species exposure. The major fish allergen characterized is parvalbumin in addition to several less well-known allergens. This contemporary review discusses interesting and new findings in the area of fish allergy including demographics, novel allergens identified, immunological mechanisms of sensitization, and innovative approaches in diagnosing and managing this life-long disease.
The role of T cell subpopulations in human disease is in a transition phase due to continuous discovery of new subsets of T cell, one of which is Th17, characterized by the production of signature cytokine IL-17. In the last couple of years, many articles are coming out on the role of Th17 and its signature cytokine IL-17 in different autoimmune diseases like rheumatoid arthritis, psoriasis, psoriatic arthritis (PsA), SLE and multiple sclerosis. Psoriasis and PsA are immune-mediated diseases, affecting the skin and joints, respectively. Initially, it was thought that psoriasis and PsA were Th1-mediated diseases; however, studies in knockout animal models (IL-17 knockout mice) as well as human experimental data indicate that Th17 and its signature cytokine IL-17 have a critical role in the pathogenesis of psoriatic disease. Th17 cells have been identified from the dermal extracts of psoriatic lesions. Subsequently, our research group has substantiated this observation that Th17 cells are enriched in the papillary dermis of psoriatic plaques and in freshly isolated effector T lymphocytes from the synovial fluid of PsA patients, and we have reported that the majority of these CD4 + IL-17+ T cells are of memory phenotype (CD4RO+CD45RA−CD11a+). Recent reports also suggest that the synovial tissue in psoriatic arthritis is enriched with IL-17R, and its most well recognized receptor IL-17RA is functionally active in psoriatic arthritis. In this review article, we have discussed the role of IL-17 in psoriatic disease and have narrated about the novel IL17/IL-17R antibodies currently in preparation for its therapeutic uses in autoimmune diseases.
The liver is a unique organ with respect to its anatomical location, allowing continuous blood flow from the gastrointestinal tract through the sinusoids, and its cellular composition, comprising metabolically active hepatocytes, nonhepatocytic parenchymal cells, and various immune cell populations. Cytokines are key mediators within the complex interplay of intrahepatic immune cells and hepatocytes, as they can activate effector functions of immune cells, as well as hepatocytic intracellular signaling pathways controlling cellular homeostasis. Kupffer cells and liver-infiltrating monocyte-derived macrophages are primary sources of cytokines such as tumor-necrosis factor-alpha (TNF-alpha) and interleukin-6. The liver is also enriched in natural killer (NK) and NK T cells, which fulfill functions in pathogen defense, T cell recruitment, and modulation of liver injury. TNF-alpha can activate specific intracellular pathways in hepatocytes that influence cell fate in different manners, e.g., proapoptotic signals via the caspase cascade, but also survival pathways, namely the nuclear factor (NF)-kappaB pathway. NF-kappaB regulates important functions in liver physiology and pathology. Recent experiments with genetically modified mice demonstrated important and partly controversial functions of this pathway, e.g., in cytokine-mediated hepatocyte apoptosis or ischemia–reperfusion injury. The exact dissection of the contribution of recruited and resident immune cells, their soluble cytokine and chemokine mediators, and the intracellular hepatocytic response in liver homeostasis and injury could potentially identify novel targets for the treatment of acute and chronic liver disease, liver fibrosis, or cirrhosis.
Autoimmune diseases are characterized by tissue damage and loss of function due to an immune response that is directed against specific organs. This review is focused on the role of impaired intestinal barrier function on autoimmune pathogenesis. Together with the gut-associated lymphoid tissue and the neuroendocrine network, the intestinal epithelial barrier, with its intercellular tight junctions, controls the equilibrium between tolerance and immunity to non-self antigens. Zonulin is the only physiologic modulator of intercellular tight junctions described so far that is involved in trafficking of macromolecules and, therefore, in tolerance/immune response balance. When the zonulin pathway is deregulated in genetically susceptible individuals, autoimmune disorders can occur. This new paradigm subverts traditional theories underlying the development of these diseases and suggests that these processes can be arrested if the interplay between genes and environmental triggers is prevented by re-establishing the zonulin-dependent intestinal barrier function. Both animal models and recent clinical evidence support this new paradigm and provide the rationale for innovative approaches to prevent and treat autoimmune diseases.
Pyoderma gangrenosum (PG) and Sweet's syndrome (SS) are skin diseases usually presenting with recurrent ulcers and erythematous plaques, respectively. The accumulation of neutrophils in the skin, characteristic of these conditions, led to coin the term of neutrophilic dermatoses to define them. Recently, neutrophilic dermatoses have been included in the group of autoinflammatory diseases, which classically comprises genetically determined forms due to mutations of genes regulating the innate immune response. Both PG and SS are frequently associated with inflammatory bowel diseases (IBDs); however, IBD patients develop PG in 1-3 % of cases, whereas SS is rarer. Clinically, PG presents with deep erythematous-to-violaceous painful ulcers with well-defined borders; bullous, pustular, and vegetative variants can also occur. SS is characterized by the abrupt onset of fever, peripheral neutrophilia, tender erythematous skin lesions, and a diffuse neutrophilic dermal infiltrate. It is also known as acute febrile neutrophilic dermatosis. Treatment of PG involves a combination of wound care, topical medications, antibiotics for secondary infections, and treatment of the underlying IBD. Topical therapies include corticosteroids and the calcineurin inhibitor tacrolimus. The most frequently used systemic medications are corticosteroids and cyclosporine, in monotherapy or in combination. Dapsone, azathioprine, cyclophosphamide, methotrexate, intravenous immunoglobulins, mycophenolate mofetil, and plasmapheresis are considered second-line agents. Hyperbaric oxygen, as supportive therapy, can be added. Anti-TNF-alpha agents such as etanercept, infliximab, and adalimumab are used in refractory cases. SS is usually responsive to oral corticosteroids, and the above-mentioned immunosuppressants should be considered in resistant or highly relapsing cases.
Chitin, a potential allergy-promoting pathogen-associated molecular pattern (PAMP), is a linear polymer composed of N-acetylglucosamine residues which are linked by β-(1,4)-glycosidic bonds. Mammalians are potential hosts for chitin-containing protozoa, fungi, arthropods, and nematodes; however, mammalians themselves do not synthetize chitin and thus it is considered as a potential target for recognition by mammalian immune system. Chitin is sensed primarily in the lungs or gut where it activates a variety of innate (eosinophils, macrophages) and adaptive immune cells (IL-4/IL-13 expressing T helper type-2 lymphocytes). Chitin induces cytokine production, leukocyte recruitment, and alternative macrophage activation. Intranasal or intraperitoneal administration of chitin (varying in size, degree of acetylation and purity) to mice has been applied as a routine approach to investigate chitin’s priming effects on innate and adaptive immunity. Structural chitin present in microorganisms is actively degraded by host true chitinases, including acidic mammalian chitinases and chitotriosidase into smaller fragments that can be sensed by mammalian receptors such as FIBCD1, NKR-P1, and RegIIIc. Immune recognition of chitin also involves pattern recognition receptors, mainly via TLR-2 and Dectin-1, to activate immune cells to induce cytokine production and creation of an immune network that results in inflammatory and allergic responses. In this review, we will focus on various immunological aspects of the interaction between chitin and host immune system such as sensing, interactions with immune cells, chitinases as chitin degrading enzymes, and immunologic applications of chitin.
Sarcoidosis has innumerable clinical manifestations, as the disease may affect every body organ. Furthermore, the severity of sarcoidosis involvement may range from an asymptomatic state to a life-threatening condition. This manuscript reviews a wide variety of common and less common clinical characteristics of sarcoidosis. These manifestations are presented organ by organ, although additional sections describe systemic and multiorgan presentations of sarcoidosis. The lung is the organ most commonly involved with sarcoidosis with at least 90 % of sarcoidosis patients demonstrating lung involvement in most series. The skin, eye, liver, and peripheral lymph node are the next most commonly clinically involved organs in most series, with the frequency of involvement ranging from 10 to 30 %. The actual frequency of sarcoidosis organ involvement is probably much higher as it is frequently asymptomatic and may avoid detection. This is particularly common with lung, liver, cardiac, and bone involvement. Cardiac sarcoidosis is present in 25 % of all sarcoidosis but only causes clinical problems in 5 % of them. Nevertheless, unlike sarcoidosis involvement of most other organs, it may be suddenly fatal. Therefore, it is important to screen for cardiac sarcoidosis in all sarcoidosis patients. All sarcoidosis patients should also be screened for eye involvement as asymptomatic patients may have eye involvement that may cause permanent vision impairment. Pulmonary fibrosis from sarcoidosis is usually slowly progressive but may be life-threatening because of the development of respiratory failure, pulmonary hypertension, or hemoptysis related to a mycetoma or bronchiectasis. Some manifestations of sarcoidosis are not organ-specific and probably are the result of a release of mediators from the sarcoid granuloma. Two such manifestations include small fiber neuropathy and fatigue syndromes, and they are observed in a large percentage of patients.
Autoimmune subepidermal blistering diseases of the skin and mucosae constitute a large group of sometimes devastating diseases, encompassing bullous pemphigoid, gestational pemphigoid, mucous membrane pemphigoid, epidermolysis bullosa acquisita, and anti-p200 pemphigoid. Their clinical presentation is polymorphic. These autoimmune blistering diseases are associated with autoantibodies that target distinct components of the basement membrane zone of stratified epithelia. These autoantigens represent structural proteins important for maintenance of dermo-epidermal integrity. Bullous pemphigoid (BP) is the most common subepidermal autoimmune blistering disease of the skin and mucosae. Although the disease typically presents with a generalized blistering eruption associated with itch, atypical variants with either localized bullous lesions or “non-bullous” presentations are observed in approximately 20% of patients. A peculiar form of BP typically associated with pregnancy is pemphigoid gestationis. In anti-p200 pemphigoid, patients present with tense blisters on erythematosus or normal skin resembling BP, with a predilection for acral surfaces. These patients have antibodies targeting the 200-kDa basement membrane protein. Epidermolysis bullosa is a rare autoimmune blistering disease associated with autoantibodies against type VII collagen that can have several phenotypes including a classical form mimicking dystrophic epidermolysis bullosa, an inflammatory presentation mimicking BP, or mucous membrane pemphigoid-like lesions. Mucous membrane pemphigoid (MMP) is the term agreed upon by international consensus for an autoimmune blistering disorder, which affects one or more mucous membrane and may involve the skin. The condition involves a number of different autoantigens in the basement membrane zone. It may result in severe complications from scarring, such as blindness and strictures. Diagnosis of these diseases relies on direct immunofluorescence microscopy studies and immunoserological assays. Management of affected patients is often challenging. We will here review the clinical and immunopathological features as well as the pathophysiology of this group of organ-specific autoimmune diseases. Finally, we will discuss the diagnostic approach and the principles of management in clinical practice.
Due to the female predominance of autoimmune diseases, the role of gender and sex hormones in the immune system is of long-term interest. Estrogen's primary effects are mediated via estrogen receptors alpha and beta (ER α/β) that are expressed on most immune cells. ERs are nuclear hormone receptors that can either directly bind to estrogen response elements in gene promoters or serve as cofactors with other transcription factors (i.e., NFkB/AP1). Cytoplasmic ER and membrane associated ER impact specific kinase signaling pathways. ERs have prominent effects on immune function in both the innate and adaptive immune responses. Genetic deficiency of ERα in murine models of lupus resulted in significantly decreased disease and prolonged survival, while ERβ deficiency had minimal to no effect in autoimmune models. The protective effect of ERα in lupus is multifactoral. In arthritis models, ERα agonists appears to mediate a protective effect. The modulation of ERα function appears to be a potential target for therapy in autoimmunity.