The infectious aspects of atopic dermatitis

The multifunctional role of filaggrin in allergic skin disease

Filaggrin is a major structural protein in the stratum corneum of the epidermis. Mutations in the filaggrin gene are the most significant known genetic risk factor for the development of atopic dermatitis. Mutations in the human filaggrin gene (FLG) also confer risk for the associated allergic diseases of food allergy, asthma, and allergic rhinitis. These discoveries have highlighted the importance of skin barrier function in the pathogenesis of atopic diseases and have motivated a surge in research characterizing the filaggrin-deficient skin barrier and its consequences. In this review we discuss the mechanisms through which mutations in this protein contribute to the pathogenesis of atopic dermatitis and associated atopic conditions. We focus on recent human and murine discoveries characterizing the filaggrin-deficient epidermis with respect to biophysical, immunologic, and microbiome abnormalities.

Atopic dermatitis in adults: clinical and epidemiological considerations

OBJECTIVE

Atopic dermatitis (AD) is a chronic inflammatory disease causing intense pruritus, and with typical clinical features. There are few epidemiological studies concerning AD in adults, as well as little information about its prognostic. The aim of this study was to evaluate the clinical and epidemiological course of adults with AD.

METHODS

80 patients aged above 18 years (mean age=29 years) were selected (30 males and 50 females) and interviewed about hospitalization, systemic corticoid usage, age of AD onset, and personal and/or familial history of atopy. Disease severity was evaluated through the Scoring Atopic Dermatitis (SCORAD) tool. Laboratory examination included IgE serum levels and eosinophil blood count.

RESULTS

71 out of 80 patients referred association with respiratory symptoms (18 had asthma, 17 had rhinitis, and 36 had both conditions); nine out of 80 patients denied any respiratory disease. AD patients were divided in mild (n=25), moderate (n=30), and severe (n=25); 56% had one or more hospitalizations due to AD. A positive association was found between IgE serum levels, eosinophil blood count, and disease severity.

CONCLUSION

Adult AD represents a clinical challenge that needs to be better characterized, since it can be misdiagnosed and interferes with the patient's social and personal life. The association of skin and respiratory atopic disease is frequent, and laboratory parameters such as circulating IgE levels and eosinophil blood count may be helpful to assess disease severity.

Management of difficult-to-treat atopic dermatitis

Atopic dermatitis is a complex disorder caused by the interplay between multiple genetic and environmental factors. Particularly in patients with severe disease, the effect is not just an itchy rash but also the secondary effects on the psychological well-being of the patient and their carers, particularly disturbed sleep. The aim of this review is to provide health care professionals with a holistic approach to the management of difficult-to-treat atopic dermatitis, defined as atopic dermatitis seemingly unresponsive to simple moisturizers and mild potency (classes VI and VII) topical corticosteroids. The critical importance of education and advice is emphasized, as is the seminal role of secondary bacterial infection and polyclonal T-cell activation in causing acute flares in patients with severe, generalized disease. In atypical cases or those that do not respond to treatment, alternative diagnoses should be considered.

Activation of epidermal toll-like receptor 2 enhances tight junction function: implications for atopic dermatitis and skin barrier repair

Atopic dermatitis (AD) is characterized by epidermal tight junction (TJ) defects and a propensity for Staphylococcus aureus (S. aureus) skin infections. S. aureus is sensed by many pattern recognition receptors including toll-like receptor (TLR) 2. We hypothesized that an effective innate immune response will include skin barrier repair and that this response is impaired in AD subjects. S. aureus-derived peptidoglycan (PGN) and synthetic TLR2 agonists enhanced TJ barrier and increased expression of TJ proteins, CLDN1, CLDN23, occludin and ZO-1 in primary human keratinocytes. A TLR2 agonist enhanced skin barrier recovery in human epidermis wounded by tape-stripping. Tlr2^−/− mice had a delayed and incomplete barrier recovery following tape-stripping. AD subjects had reduced epidermal TLR2 expression as compared to nonatopic (NA) subjects, which inversely correlated (r= 0.654, P= 0.0004) with transepidermal water loss (TEWL). These observations indicate that TLR2 activation enhances skin barrier in murine and human skin and is an important part of a wound repair response. Reduced epidermal TLR2 expression observed in AD patients may play a role in their incompetent skin barrier.

Abnormal epidermal barrier in the pathogenesis of atopic dermatitis

Despite the acknowledged contributions of a defective epidermal permeability barrier, dryness of the skin, and the propensity to develop secondary infections to the etiology and pathophysiology of atopic dermatitis (AD), these epidermal changes have, until recently, been assumed to reflect downstream consequences that are secondary phenomena of the primary immunologic abnormality--the historical "inside-outside" view that AD is basically an intrinsic inflammatory disease. In this review, we focused on the role of the epidermal barrier function in the pathophysiology of AD. Specifically, we presented data in support of a barrier-initiated pathogenesis of AD, ie, the "outside-inside" concept. First, we reviewed the evidence on the existence of inherited barrier abnormalities in AD. Reported studies on the possible association of mutations in the filaggrin gene (FLG) and data on human tissue kallikreins (KLKs) and AD have been addressed. We then dealt with the question of the causal link between impaired epidermal barrier and inflammation. Finally, the association between innate immune defense system and the increased avidity of Staphylococcus aureus for atopic skin was examined. Despite very convincing evidence to support the barrier-initiated pathogenesis of AD, the view that AD reflects the downstream consequences of a primary immunologic abnormality cannot be dismissed out of hand. Almost every line of evidence in support of the role of the epidermal barrier as the "driver" of the disease activity can be challenged and at least partially contradicted by opposing evidence. Until more data are available and until all the dust settles around this issue, we should take advantage of what we already know and use our knowledge for practical purposes. Deployment of specific strategies to restore the barrier function in AD means the use of moisturizers as first-line therapy.

Severe chronic allergic (and related) diseases: a uniform approach--a MeDALL--GA2LEN--ARIA position paper

Concepts of disease severity, activity, control and responsiveness to treatment are linked but different. Severity refers to the loss of function of the organs induced by the disease process or to the occurrence of severe acute exacerbations. Severity may vary over time and needs regular follow-up. Control is the degree to which therapy goals are currently met. These concepts have evolved over time for asthma in guidelines, task forces or consensus meetings. The aim of this paper is to generalize the approach of the uniform definition of severe asthma presented to WHO for chronic allergic and associated diseases (rhinitis, chronic rhinosinusitis, chronic urticaria and atopic dermatitis) in order to have a uniform definition of severity, control and risk, usable in most situations. It is based on the appropriate diagnosis, availability and accessibility of treatments, treatment responsiveness and associated factors such as comorbidities and risk factors. This uniform definition will allow a better definition of the phenotypes of severe allergic (and related) diseases for clinical practice, research (including epidemiology), public health purposes, education and the discovery of novel therapies.

Staphylococcus aureus α-toxin modulates skin host response to viral infection

BACKGROUND

Patients with atopic dermatitis (AD) with a history of eczema herpeticum have increased staphylococcal colonization and infections. However, whether Staphylococcus aureus alters the outcome of skin viral infection has not been determined.

OBJECTIVE

We investigated whether S aureus toxins modulated host response to herpes simplex virus (HSV) 1 and vaccinia virus (VV) infections in normal human keratinocytes (NHKs) and in murine infection models.

METHODS

NHKs were treated with S aureus toxins before incubation of viruses. BALB/c mice were inoculated with S aureus 2 days before VV scarification. Viral loads of HSV-1 and VV were evaluated by using real-time PCR, a viral plaque-forming assay, and immunofluorescence staining. Small interfering RNA duplexes were used to knockdown the gene expression of the cellular receptor of α-toxin, a disintegrin and metalloprotease 10 (ADAM10). ADAM10 protein and α-toxin heptamers were detected by using Western blot assays.

RESULTS

We demonstrate that sublytic staphylococcal α-toxin increases viral loads of HSV-1 and VV in NHKs. Furthermore, we demonstrate in vivo that the VV load is significantly greater (P < .05) in murine skin inoculated with an α-toxin-producing S aureus strain compared with murine skin inoculated with the isogenic α-toxin-deleted strain. The viral enhancing effect of α-toxin is mediated by ADAM10 and is associated with its pore-forming property. Moreover, we demonstrate that α-toxin promotes viral entry in NHKs.

CONCLUSION

The current study introduces the novel concept that staphylococcal α-toxin promotes viral skin infection and provides a mechanism by which S aureus infection might predispose the host toward disseminated viral infections.

Association between atopic dermatitis and obesity in adulthood

BACKGROUND

Obesity in early childhood is associated with increased risk for and severity of atopic dermatitis (AD). Objective To determine whether obesity in adulthood is associated with risk of AD.

METHODS

This was a retrospective case-control study of 2090 adults using questionnaire, height and weight, and skin-prick testing between January 1994 and December 2003.

RESULTS

Obesity in adults was associated with increased AD [multinomial logistic regression: adjusted odds ratio (aOR) 1·43, 95% confidence interval (CI) 1·08-1·89; P=0·01], but not nonatopic dermatitis (aOR 0·59, 95% CI 0·21-1·68; P=0·32). Obesity was also associated with increased atopic asthma (aOR 1·98, 95% CI 1·47-2·66, P<0·0001), but not associated with nonatopic asthma (P=0·20), atopic or nonatopic rhinoconjunctivitis (P=0·08 and 0·31, respectively), food allergies (P=0·67 and 0·35, respectively) or atopy (P=0·40). The association between obesity and AD remained significant even when controlling for history of asthma, rhinoconjunctivitis and food allergies (aOR 1·40, 95% CI 1·05-1·86; P=0·02) or in subset analyses of subjects with AD alone (aOR 1·96, 95% CI 1·02-3·75; P=0·04) and with comorbid asthma, rhinoconjunctivitis and/or food allergies (aOR 1·40, 95% CI 1·03-1·91; P=0·03).

CONCLUSION

Obesity in adulthood is associated with AD. Further studies are warranted to determine if weight loss may prevent or mitigate AD in adults.

Ten warning signs of primary immunodeficiency: a new paradigm is needed for the 21st century

The 10 warning signs of primary immunodeficiency are being promoted as a screening tool for use by both the general public and physicians. A recent study, however, shows that except for family history, need for intravenous antibiotics and failure to thrive, the 10 warning signs are not a useful screen of primary immunodeficiency diseases (PIDs). Over the last few decades, there has been a revolution in our understanding of PID. The 10 warning signs do not take into account the fact that PIDs now include diseases that present with sporadic infections, autoimmunity, autoinflammation, and malignancy. This review focuses on the advances in our understanding of PID, the current limitations of the 10 warning signs, and recommendations to ensure that patients with PID are diagnosed in a timely fashion in the future.

Eczema

Atopic dermatitis, commonly known as eczema, is a common chronic, relapsing skin disease characterized by pruritus, disrupted epidermal barrier function, and immunoglobulin E-mediated sensitization to food and environmental allergens. Atopic dermatitis is a complex disease that arises from interactions between genes and the environment. Loci on several chromosomes have been identified, including a family of epithelium-related genes called the epidermal differentiation complex on chromosome 1q21. Mutations in filaggrin, a key protein in epidermal differentiation, have also been identified in early-onset and severe atopic dermatitis. There are 3 classical stages of eczema: infantile, childhood, and adulthood. The spectrum of eczema presentation varies widely from a variant that only affect the hand to major forms where a patient presents with erythroderma. The acute and subacute lesions of atopic dermatitis are often characterized by intensely pruritic, erythematous papules and vesicles with excoriations and a serous exudate. Chronic atopic dermatitis is exemplified by lichenified plaques and papules with excoriations. Atopic dermatitis patients are also at higher risk for skin infections, including bacterial and viral superinfections. Conventional therapy includes avoidance of irritants and potential allergens, as well as continued hydration of the skin with thick emollients. Topical corticosteroids and topical immunomodulators are often used primarily. Other therapies including phototherapy, antimicrobials, antihistamines, and systemic immunosuppressives are also options in certain situations.