Immune dysregulation in atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease in humans and dogs with comparable clinical features. Comparative studies of immunological events in the pathogenesis of AD may contribute to understanding of the disease in dogs and to development and evaluation of immunomodulatory strategies of relevance to both species.Both allergen-specific as well as non-specific mechanisms contribute to the disease development. AD skin lesions are proposed to be initiated by activation of allergen-specific Th2-type cells, potentially influenced by local cutaneous factors. In the chronic stage of skin lesions reactivity may change into a Th1-type, e.g. driven by eosinophil derived IL-12. Analyses of these processes in course of time were performed in both spontaneous as well as in experimentally induced lesions (i.e. atopy patch test (APT) lesions). In the present paper, the immunological events as reported for human and canine AD are summarized and compared.     

Fixing the skin barrier: past,present and future – man and dog compared

Skin barrier dysfunction exists in both human and canine atopic dermatitis, leading to increased water loss and potentially facilitating allergen penetration and sensitization. Both lipid (e.g. ceramides) and protein (e.g. filaggrin) abnormalities have been described. Some are genetically inherited (e.g. filaggrin mutations are one of the major risk factors in humans) and some are secondary and linked to inflammation. In humans, numerous studies have shown efficacy of emollients and moisturizers in barrier restoration, and this approach has been for years the mainstay of therapy. Recently, this strategy has shown promise as a preventative function. In veterinary medicine, evidence regarding skin barrier impairment is rapidly building. Decreased ceramides and filaggrin (in some subsets of dogs) have been described. Altered metabolism of ceramides has also been proposed. Despite these preliminary data and the availability of products marketed to improve the skin barrier, evidence regarding the clinical benefit of skin repair intervention is still limited. Preliminary studies have demonstrated that topical application of fatty acids and ceramides and systemic administration of fatty acids improve lipid deficiencies in the skin of dogs with atopic dermatitis, but limited clinical evidence exists. Disease remission in humans is paralleled by an improved skin barrier, both with calcineurin inhibitors and glucocorticoids. In veterinary medicine, a preliminary study on ciclosporin and prednisone failed to detect significant improvement of water loss, while successful immunotherapy correlated with an improved skin barrier. Controlled, large studies are needed to address the question of which skin repair approach is clinically most effective and whether this can be used as a preventative strategy.     

Expression analysis of CCL27 and CCL28 mRNA in lesional and non-lesional skin of dogs with atopic dermatitis

Chemokines are important regulators of the selective recruitment of inflammatory cells into sites of allergic inflammation. Since canine atopic dermatitis (AD) shares many clinical features of human AD, patterns of chemokine production in dogs may also be similar with those in humans. The aim of this study was to examine mRNA expression of CCL27 and CCL28 in lesional skin of dogs with AD to demonstrate similarity of chemokine production with human counterparts. RNA was extracted from skin biopsy specimens of 12 dogs with AD. The mRNA expression of CC chemokines (CCL4, CCL19, CCL20, CCL21, CCL24, CCL27 and CCL28) was analyzed by quantitative real-time PCR and was compared between lesional and non-lesional skin. Seven types of chemokines examined were constitutively expressed in both lesional and non-lesional skin. It was found that mRNA expression levels of CCL27 and CCL28 among the chemokines were significantly different between lesional and non-lesional skin (P<0.05). Expression level of CCL27 mRNA in lesional skin was significantly lower than that in non-lesional skin. On the other hand, CCL28 mRNA expression in lesional skin was found to be higher than that in non-lesional skin. These results suggest that CCL28 but not CCL27 may play important roles in immunopathogenesis of canine AD, indicating that experimental canine study may provide additional information that can be extrapolated to human AD.     

犬特应性皮炎及其治疗药物的研究进展

犬特应性皮炎是一种具有遗传倾向的过敏性皮肤病。由于近年来我国养犬数量不断增加,犬特应性皮炎成为宠物临床上的常见疾病,严重危害了宠物犬的身体健康。该病病因复杂,大致可概括为遗传因素、环境因素、皮肤屏障功能失调、免疫功能失调和微生物菌群失调五个方面,且由于其临床症状与其他过敏反应、炎症反应相似,难以确诊,需要通过多种临床反应共同判定。随着小动物诊疗的不断发展,犬特应性皮炎治疗在以往基础疗法上又增加了使用抗炎止痒药物、JAK通路抑制药物、生物制品药物和PED-4 选择性抑制剂等治疗方式。本文综述了近年来犬特应性皮炎的病因、临床症状、诊断方法和治疗方法方面的研究进展,以期为犬特应性皮炎的治疗提供借鉴和参考。     

Characterization and quantification of ceramides in the nonlesional skin of canine patients with atopic dermatitis compared with controls

As in humans, there is mounting evidence in support of an abnormal skin barrier contributing to the pathogenesis of canine atopic dermatitis (AD). Studies in people with AD have associated an abnormal skin barrier with deficiencies in ceramides, which represent important components of the stratum corneum (SC) intercellular lipid lamellae. Therefore, the goal of this study was to determine if the SC of dogs with AD is deficient in ceramides compared to normal dogs. Samples of SC were obtained from nonlesional skin of the caudal abdomen of 14 patients with AD and 14 age-, breed- and sex-matched healthy controls using a cyanoacrylate stripping procedure, and the subclass and relative amount of ceramides were assessed blindly by thin layer chromatography. Paired t -tests using R statistical computer software revealed the percentage amounts of ceramides 1 and 9 were significantly lower in nonlesional skin of AD dogs compared to controls ( P = 0.034 and P = 0.047, respectively), and the cholesterol percentage amount was significantly higher in AD dogs than in controls ( P = 0.016). Furthermore, the cholesterol/ceramide ratio was significantly higher in the AD group with respect to controls ( P = 0.014). These findings suggest that decreased amounts of ceramides in the skin of dogs with AD may be involved in the impaired barrier function of their skin.     

The ACVD task force on canine atopic dermatitis (XX): glucocorticoid pharmacotherapy.

Glucocorticoids (GCs) have been the most commonly prescribed drugs for treatment of canine atopic dermatitis (AD) during the last decades. In spite of this widespread usage, there are a few studies documenting their efficacy. Fortunately, recently completed clinical trials were designed with oral GCs used as "standard of care" for treatment of canine AD. These studies provided high quality evidence in favor of the strong efficacy of oral low-dose glucocorticoid formulations to control skin lesions and pruritus in dogs with AD. Consequently, there is good evidence to support the recommendation of use of oral glucocorticoids for treatment of canine AD.     

Evaluation of the expression of P-selectin, ICAM-1, and TNF-alpha in bacteria-free lesional skin of atopic dogs with low-to-mild inflammation

Canine atopic dermatitis (AD) is a pruritic skin condition that shares many clinical and pathophysiological features with its human counterpart. A major therapeutic challenge of AD is the control of the skin inflammatory process. A detailed knowledge of the pro-inflammatory molecules involved in cell recruitment in AD would allow for a better control of the disease. We thus have studied the protein expression of P-selectin, ICAM-1 and TNF-alpha in the lesional and non-lesional skin of atopic dogs that had been treated for bacterial infections. Despite a low-to-mild inflammatory process, P-selectin protein was clearly upregulated in the lesional skin areas when compared with non-lesional skin (four-fold average increase). This P-selectin upregulation was accompanied by signs of functional changes such as increased cell margination, and membrane-associated protein expression. Although the expression of ICAM-1 and TNF-alpha was not enhanced in the lesional versus the non-lesional skin, there was a trend towards a correlated upregulation of both molecules. Further studies will help elucidate the significance of the substantial overexpression of P-selectin in canine AD, in particular in a scenario where bacterial antigens are not contributing as pro-inflammatory stimuli.     

Recent developments in canine atopic dermatitis: a review

Atopic dermatitis (AD) is a genetically predisposed inflammatory and pruritic allergic skin disease with characteristic clinical features. New results on the pathogenesis and therapeutic aspects are discussed in this review. IgE-mediated hypersensitivity may be involved in the largest subset of atopic patients, yet there is another subset for which such involvement cannot be documented. Alterations in epidermal barrier function, priming of cutaneous antigen-presenting cells with IgE, intrinsic keratinocyte defects, and development of autoimmunity are also factors that contribute to the primary disease. Polymorphisms in regions of the genome that are of key importance to the inflammatory response contribute to the patient's clinical picture. Secondary infections, especially with Staphylococcus and yeast organisms, strongly modify or augment the inflammatory response, which changes over time. After the treatment of secondary infections and skin inflammation the avoidance of causal allergens would prevent relapse. Another causative therapy is the variously effective allergen-specific immunotherapy. The newest treatments for canine AD (cyclosporin A and tacrolimus) are highly effective at suppressing the allergic response and comparable to treatment with glucocorticoids. Canine AD presents a substantial diagnostic and therapeutic challenge over a patient's lifetime, and no single treatment is universally effective.     

Expression of CC chemokine receptor 4 (CCR4) mRNA in canine atopic skin lesion

CC chemokine receptor 4 (CCR4) is a G protein-coupled seven transmembrane receptor that is selectively expressed on Th2 cells and plays an important role in the trafficking of Th2 cells into inflammatory sites. In this study, a full-length canine CCR4 cDNA was cloned and characterized in order to examine the potential role of CCR4 in allergic responses that produce skin lesions in canine atopic dermatitis (AD). The canine CCR4 cDNA reported in this study contained an open reading frame of 1083 nucleotides encoding 360 amino acids. The predicted amino acid sequence of canine CCR4 showed 91.9, 85.3 and 84.5% similarity with those of the human, mouse and guinea pig counterparts, respectively. Expression of CCR4 mRNA was detected in various tissues including thymus, spleen, heart, small intestine and lymph node. Furthermore, it was found that CCR4 mRNA was preferentially expressed in lesional skin of dogs with AD, together with the mRNA of thymus and activation-regulated chemokine (TARC), which is a ligand for CCR4. The present study demonstrates that CCR4 contributes strongly to the immunopathogenesis of canine AD.     

Clinical use of a ceramide-based moisturizer for treating dogs with atopic dermatitis

In humans, skin barrier dysfunction is thought to be responsible for enhanced penetration of allergens. Similar to conditions seen in humans, canine atopic dermatitis (CAD) is characterized by derangement of corneocytes and disorganization of intercellular lipids in the stratum corenum (SC) with decreased ceramide levels. This study was designed to evaluate the effects of a moisturizer containing ceramide on dogs with CAD. Dogs (n = 20, 3~8 years old) with mild to moderate clinical signs were recruited and applied a moisturizer containing ceramide for 4 weeks. Transepidermal water loss (TEWL), skin hydration, pruritus index for canine atopic dermatitis (PICAD) scores, and canine atopic dermatitis extent and severity index (CADESI) scores of all dogs were evaluated. Skin samples from five dogs were also examined with transmission electron microscopy (TEM) using ruthenium tetroxide. TEWL, PICAD, and CADESI values decreased (p < 0.05) and skin hydration increased dramatically over time (p < 0.05). Electron micrographs showed that the skin barrier of all five dogs was partially restored (p < 0.05). In conclusion, these results demonstrated that moisturizer containing ceramide was effective for treating skin barrier dysfunction and CAD symptoms.     

Is the skin barrier abnormal in dogs with atopic dermatitis?

In mammalian skin, the stratum corneum exerts a barrier function that protects from transepidermal water loss and the penetration of exogenous molecules, such as allergens, from the environment. Recently, skin barrier defects have been shown to be of prime importance in the pathogenesis of human atopic dermatitis. In this review, we summarize the latest research data pertinent to the stratum corneum and barrier function of dogs with atopic dermatitis. At the time of this writing, there is increasing evidence that a skin barrier defect likely exists in dogs with atopic dermatitis. This barrier dysfunction is characterized by abnormal intercellular stratum corneum lipid lamellae, abnormal stratum corneum morphology, reduced and abnormal ceramide content and, in some but not all dogs, abnormal filaggrin expression. In association with these changes, there is higher transepidermal water loss in atopic than in normal canine skin. Furthermore, atopic inflammation appears to worsen transepidermal water loss and filaggrin expression. It remains unknown, however, if the changes observed are primary (i.e. of genetic origin) or secondary to atopic inflammation that also exists even in clinically normal skin. Finally, whether or not a therapeutic intervention aimed at restoring a dysfunctional skin barrier is of any clinical benefit to atopic dogs has not yet been proven unequivocally.     

A systematic review of randomized controlled trials for prevention or treatment of atopic dermatitis in dogs: 2008–2011 update

Background – The management of atopic dermatitis (AD) in dogs relies mainly on the use of interventions to reduce pruritus and skin lesions. Objectives – To provide a critical analysis of recent clinical trials reporting the efficacy and safety of interventions for canine AD. Methods – Systematic review of randomized controlled trials (RCTs) published, presented or completed between 2008 and 2011, which enrolled dogs with AD. The search was done using electronic databases, reviewing published meeting abstracts and sending queries to professional email lists. Trials reporting the efficacy of interventions aimed at treating, preventing or reducing glucocorticoid usage in atopic dogs were selected. Results – Twenty‐one RCTs were included. We found further moderate‐quality evidence of efficacy and safety of oral glucocorticoids and ciclosporin for treatment of canine AD. There was additional moderate‐quality evidence of the efficacy of a topical glucocorticoid spray containing hydrocortisone aceponate. Low‐quality evidence was found for the efficacy and safety of injectable recombinant interferons, a budesonide leave‐on conditioner, a ciclosporin topical nano‐emulsion and oral fexofenadine. There is low‐quality evidence of efficacy of oral masitinib, with a need for monitoring for protein‐losing nephropathy. Finally, we uncovered low‐quality evidence of efficacy of a commercial diet as a glucocorticoid‐sparing intervention and of a glucocorticoid spray as a flare‐delaying measure. Very low‐quality evidence was found for the efficacy of other interventions. Conclusions and clinical importance – Topical or oral glucocorticoids and oral ciclosporin remain the interventions with highest evidence for efficacy and relative safety for treatment of canine AD.     

Electron microscopic observations of stratum corneum intercellular lipids in normal and atopic dogs.

The barrier function of mammalian skin is maintained by intercellular stratum corneum lipids. In human patients with atopic dermatitis, an abnormal lipid barrier results in dry skin and increased transepidermal water loss. At this time, it is not known if a defective lipid barrier is present in atopic dogs. Normal and atopic canine skin were postfixed in ruthenium tetroxide and studied using transmission electron microscopy to determine structural differences within stratum corneum lipids. Intercellular lipid lamellae were graded on a semiquantitative scale. The deposition of stratum corneum lipid lamellae in atopic canine skin appeared markedly heterogeneous compared with that seen in normal canine skin. When present, the lamellae often exhibited an abnormal structure. The continuity and thickness of the intercellular lipid lamellae were significantly less in nonlesional atopic than in normal canine skin. These preliminary observations suggest that the epidermal lipid barrier is defective in atopic canine skin. Additional studies are needed to further characterize the biochemical defect and to possibly correct it with nutritional and/or pharmacologic intervention.     

Epithelial–immune crosstalk with the skin microbiota in homeostasis and atopic dermatitis – a mini review

The skin is a complex and dynamic ecosystem, wherein epithelial cells, immune cells and the skin microbiota actively interact and maintain barrier integrity and functional immunity. Skin microbes actively tune the functions of the resident immune cells. Dysbiosis – alterations in the resident microbiota – leads to the dysregulation of host immunity. Microbiome analyses in humans and dogs with atopic dermatitis (AD) have shown shifts in microbial diversity, and in particular, an increased proportion of staphylococci. Monogenic diseases that manifest AD-like symptoms provide insights into the pathogenesis of AD and the mechanisms of dysbiosis, from both the epithelial and immunological perspectives. The symbiotic relationships between the host and microbiota must be maintained constitutively. Detailed mechanisms of how host immunity regulates commensal bacteria in the steady state have been reported. The skin harbours multiple tissue-resident immune cells, including both innate and adaptive immune cells. Recent studies have highlighted the fundamental role of innate lymphoid cells (ILCs) in the maintenance of barrier functions and tissue homeostasis. ILCs directly respond to tissue-derived signals and are instrumental in barrier immunity. Epithelial cells produce alarmins such as thymic stromal lymphopoietin (TSLP) and interleukins (IL)-33 and IL-25, all of which activate group 2 ILCs (ILC2s), which produce type 2 cytokines, such as IL-5 and IL-13, boosting type 2 immune reactions. Dysregulation of the epithelial–ILC crosstalk results in allergic inflammation. This review highlights our understanding of the active interactions between the host epithelial and immune cells, and microbiota, providing a foundation for novel therapeutic strategies for inflammatory skin diseases.     

犬瘙痒性皮肤病研究进展

瘙痒是犬皮肤病的典型临床症状之一，通常除瘙痒外还常伴脱毛、红斑等皮肤症状。瘙痒问题不仅困扰动物本身，也影响到饲养者的生活质量。瘙痒的发生机制复杂，目前国内外已有大量对人和犬瘙痒性皮肤病的临床和基础研究，揭示了瘙痒和神经免疫系统之间的关系，引入了"瘙痒-抓挠"循环的概念，且表明了免疫系统、皮肤屏障和神经系统的单独促进作用和交互作用是瘙痒产生的关键因素，任一环节的问题都可开启"瘙痒-抓挠"的恶性循环。临床上引起犬瘙痒的病因复杂，参照2007年由国际瘙痒研究论坛成员提出的瘙痒分类，将引起犬瘙痒的疾病根据病因类比对应分为了六大类，引起皮肤病性瘙痒的疾病分为了感染性、过敏性、肿瘤性等，其中在临床上最主要的是犬过敏性瘙痒。犬瘙痒性皮肤病的诊断方法及鉴别诊断多样，需从多方面对患病犬进行信息收集，按一定顺序进行排查和鉴别诊断。犬瘙痒性皮肤病的治疗周期长且疾病易反复，目前常用的西医药物存在副作用大、靶点单一、价格昂贵等不足，中药方剂成分复杂，有效成分多，可从多通路多途径治疗机制复杂的瘙痒，在犬瘙痒性皮肤病的治疗上具有优势和广阔前景。文章对瘙痒发生的机制、犬瘙痒性疾病的分类、诊断及中西医治疗思路等最新研究进展进行综述，以期为小动物临床瘙痒相关疾病的诊治提供参考依据。