2. Superantigens, steroid insensitivity and innate immunity in atopic eczema

Genetic/Environmental Contributions and Immune Dysregulation in Children with Atopic Dermatitis

Atopic dermatitis (AD) is one of the most common skin conditions in humans. AD affects up to 20% of children worldwide and results in morbidity for both patients and their caregivers. The basis of AD is an interplay between genetics and the environment characterized by immune dysregulation. A myriad of mutations that compromise the skin barrier and/or immune function have been linked to AD. Of these, filaggrin gene (FLG) mutations are the most evidenced. Many other mutations have been implicated in isolated studies that are often unreplicated, creating an archive of genes with potential but unconfirmed relevance to AD. Harnessing big data, polygenic risk scores (PRSs) and genome-wide association studies (GWAS) may provide a more practical strategy for identifying the genetic signatures of AD. Epigenetics may also play a role. Staphylococcus aureus is the most evidenced microbial contributor to AD. Cutaneous dysbiosis may result in over-colonization by pathogenic strains and aberrant skin immunity and inflammation. Aeroallergens, air pollution, and climate are other key environmental contributors to AD. The right climate and/or commensals may improve AD for some patients.

Glucocorticoid Resistance: Interference between the Glucocorticoid Receptor and the MAPK Signalling Pathways

Endogenous glucocorticoids (GCs) are steroid hormones that signal in virtually all cell types to modulate tissue homeostasis throughout life. Also, synthetic GC derivatives (pharmacological GCs) constitute the first-line treatment in many chronic inflammatory conditions with unquestionable therapeutic benefits despite the associated adverse effects. GC actions are principally mediated through the GC receptor (GR), a ligand-dependent transcription factor. Despite the ubiquitous expression of GR, imbalances in GC signalling affect tissues differently, and with variable degrees of severity through mechanisms that are not completely deciphered. Congenital or acquired GC hypersensitivity or resistance syndromes can impact responsiveness to endogenous or pharmacological GCs, causing disease or inadequate therapeutic outcomes, respectively. Acquired GC resistance is defined as loss of efficacy or desensitization over time, and arises as a consequence of chronic inflammation, affecting around 30% of GC-treated patients. It represents an important limitation in the management of chronic inflammatory diseases and cancer, and can be due to impairment of multiple mechanisms along the GC signalling pathway. Among them, activation of the mitogen-activated protein kinases (MAPKs) and/or alterations in expression of their regulators, the dual-specific phosphatases (DUSPs), have been identified as common mechanisms of GC resistance. While many of the anti-inflammatory actions of GCs rely on GR-mediated inhibition of MAPKs and/or induction of DUSPs, the GC anti-inflammatory capacity is decreased or lost in conditions of excessive MAPK activation, contributing to disease susceptibility in tissue- and disease- specific manners. Here, we discuss potential strategies to modulate GC responsiveness, with the dual goal of overcoming GC resistance and minimizing the onset and severity of unwanted adverse effects while maintaining therapeutic potential.

A rare skin infection in atopic dermatitis: A case report

Atopic dermatitis is associated with a susceptibility to infection usually by Staphylococcus spp due to a decrease of AMPs and Th2 cytokines (eg, IL-17). We reported a rare E. faecalis skin contamination in AD patients due to a frequent contact with excrement.

Skin pH-dependent Staphylococcus aureus abundance as predictor for increasing atopic dermatitis severity

BACKGROUND

Atopic eczema (atopic dermatitis, AD) is characterized by disrupted skin barrier associated with elevated skin pH and skin microbiome dysbiosis, due to high Staphylococcus aureus loads, especially during flares. Since S aureus shows optimal growth at neutral pH, we investigated the longitudinal interplay between these factors and AD severity in a pilot study.

METHOD

Emollient (with either basic pH 8.5 or pH 5.5) was applied double-blinded twice daily to 6 AD patients and 6 healthy (HE) controls for 8 weeks. Weekly, skin swabs for microbiome analysis (deep sequencing) were taken, AD severity was assessed, and skin physiology (pH, hydration, transepidermal water loss) was measured.

RESULTS

Physiological, microbiome, and clinical results were not robustly related to the pH of applied emollient. In contrast to longitudinally stable microbiome in HE, S aureus frequency significantly increased in AD over 8 weeks. High S aureus abundance was associated with skin pH 5.7-6.2. High baseline S aureus frequency predicted both increase in S aureus and in AD severity (EASI and local SCORAD) after 8 weeks.

CONCLUSION

Skin pH is tightly regulated by intrinsic factors and limits the abundance of S aureus. High baseline S aureus abundance in turn predicts an increase in AD severity over the study period. This underlines the importance and potential of sustained intervention regarding the skin pH and urges for larger studies linking skin pH and skin S aureus abundance to understand driving factors of disease progression.

Neonatal gut colonization by Staphylococcus aureus strains with certain adhesins and superantigens is negatively associated with subsequent development of atopic eczema

BACKGROUND

Insufficient early immune stimulation may predispose to atopic disease. Staphylococcus aureus, a skin and gut colonizer, produces the B-cell mitogen protein A and T-cell-activating superantigens. Early gut colonization by S. aureus strains that possess the superantigens encoded by the enterotoxin gene (egc) cluster and elastin-binding protein is negatively associated with development of atopic eczema.

OBJECTIVES

To investigate (i) whether these findings could be replicated in a second birth cohort, FARMFLORA, and (ii) whether nasal colonization by S. aureus also relates to subsequent atopic eczema development.

METHODS

Faecal samples and nasal swabs from infants in the FARMFLORA birth cohort (n = 65) were cultured for S. aureus. Individual strains were distinguished by random amplified polymorphic DNA and assessed for adhesin and superantigen gene carriage by polymerase chain reaction. Atopic eczema at 18 months of age was related to nasal and gut S. aureus colonization patterns during the first 2 months of life (well before onset of eczema).

RESULTS

Staphylococcus aureus colonization per se was unrelated to subsequent eczema development. However, gut S. aureus strains from the infants who subsequently developed atopic eczema less frequently carried the ebp gene, encoding elastin-binding protein, and superantigen genes encoded by egc, compared with strains from children who remained healthy. Nasal colonization by S. aureus was less clearly related to subsequent eczema development.

CONCLUSIONS

The results precisely replicate our previous observations and may suggest that mucosal colonization by certain S. aureus strains provides immune stimulation that strengthens the epithelial barrier and counteracts the development of atopic eczema.

Bacterial and Viral Infections in Atopic Dermatitis: a Comprehensive Review

Atopic dermatitis (AD) is the most common allergic skin disease in the general population. It is a chronic inflammatory skin disease complicated by recurrent bacterial and viral infections that, when left untreated, can lead to significant complications. The current article will review immunologic and molecular mechanisms underlying the propensity of AD patients to microbial infections. These infections include Staphylococcus aureus (S. aureus) skin infections, eczema herpeticum, eczema vaccinatum, and eczema coxsackium. Previous studies have shown that skin barrier defects, a decrease in antimicrobial peptides, increased skin pH, or Th2 cytokines such as IL-4 and IL-13 are potential contributing factors for the increased risk of skin infections in AD. In addition, bacterial virulence such as methicillin-resistant S. aureus (MRSA) produces significantly higher number of superantigens that increase their potential in causing infection and more severe cutaneous inflammation in AD patients. More recent studies suggest that skin microbiome including Staphylococcus epidermidis or other coagulase-negative staphylococci may play an important role in controlling S. aureus skin infections in AD. Other studies also suggest that genetic variants in the innate immune response may predispose AD patients to increased risk of viral skin infections. These genetic variants include thymic stromal lymphopoietin (TSLP), type I interferon (α, ß, ω), type II interferon (γ), and molecular pathways that lead to the production of interferons (interferon regulatory factor 2). A common staphylococcal toxin, α-toxin, may also play a role in enhancing herpes simplex virus skin infections in AD. Further understanding of these disease processes may have important clinical implications for the prevention and treatment of skin infections in this common skin disease.

Superantigens and adhesins of infant gut commensal Staphylococcus aureus strains and association with subsequent development of atopic eczema

BACKGROUND

According to the hygiene hypothesis, insufficient immune activation by microbes increases the risk of allergy development. Staphylococcus aureus, which is part of the skin and gut microbiota of infants in Western countries, produces a variety of T-cell-activating enterotoxins, called superantigens.

OBJECTIVES

To investigate whether early (0-2 months of age) gut colonization by S. aureus strains that carry specific superantigens and adhesins was related to subsequent development of atopic eczema in a Swedish birth cohort.

METHODS

Staphylococcus aureus was isolated from rectal swabs and cultured quantitatively from faecal samples, with individual strains being tested for carriage of genes for superantigens and adhesins. Atopic eczema was diagnosed at onset of symptoms and at 18 months of age.

RESULTS

Although the frequency of early gut colonization by S. aureus was not related to subsequent eczema development, the S. aureus strains that were found to colonize those infants who developed atopic eczema were less likely to carry the gene encoding the superantigen SElM (P = 0·008) and the gene for elastin-binding protein (P = 0·03), compared with strains that were isolated from infants who had not developed atopic eczema by 18 months of age.

CONCLUSIONS

Gut colonization by S. aureus strains carrying a certain combination of superantigen and adhesin genes was negatively associated with subsequent development of atopic eczema. Such strains may provide stimulation and promote maturation of the infant immune system.

Therapeutic approach to mite-induced intractable dermatitis using novel immunomodulator FTY720 ointment (fingolimod) in NC/Nga mice

BACKGROUND

The increasing incidence and prevalence of atopic dermatitis (AD) demands new therapeutic approaches for treating the disease. We investigated the therapeutic efficacy of immunomodulator FTY720 ointment (fingolimod) for mite-induced intractable AD using an NC/Nga mouse model.

METHODS

Female NC/Nga mice that developed severe AD were divided into four groups: (1) FTY720 (0.001% FTY720 ointment), (2) tacrolimus (tacrolimus hydrate ointment) (3) betamethasone (betamethasone ointment), and (4) ointment base (hydrophilic petrolatum), all of which received treatment six times per week. Therapeutic efficacy after two weeks was evaluated in terms of AD severity, histochemical observations (epidermal hypertrophy, mast cell accumulation, and CD3(+) T cell infiltration), transepidermal water loss (TEWL), and epidermal barrier function (filaggrin expression).

RESULTS

Betamethasone treatment showed little effect, confirming that the AD was intractable. In the FTY720 group, AD improved significantly compared with the ointment base group, as did epidermal hypertrophy, mast cell accumulation, and CD3(+) T cell infiltration. In contrast, AD in the tacrolimus and betamethasone groups did not improve significantly, nor did epidermal hypertrophy or mast cell accumulation. Furthermore, in the FTY720 group, TEWL decreased significantly compared with the ointment base group, and filaggrin expression significantly increased compared with the betamethasone and ointment base groups.

CONCLUSIONS

FTY720 ointment is a promising candidate for treatment of intractable AD. These findings also provide the first evidence that FTY720 ointment ameliorates epidermal barrier function.

Therapeutic approach to steroid-resistant dermatitis using novel immunomodulator FTY720 (Fingolimod) in combination with betamethasone ointment in NC/Nga mice

The therapeutic efficacy of the novel immunomodulator FTY720 (Fingolimod), alone and in combination with betamethasone ointment, was examined in the NC/Nga mouse model of spontaneous steroid-resistant dermatitis. Male NC/Nga mice which had developed severe dermatitis were divided into six groups: 1) a biweekly betamethasone group (betamethasone ointment, twice a week), 2) a daily betamethasone group (betamethasone ointment, six times a week), 3) an FTY720 group (FTY720, orally, three times a week), 4) a biweekly combination group (oral FTY720 plus betamethasone ointment, twice a week), 5) a daily combination group (oral FTY720 plus betamethasone ointment, six times a week) and 6) a placebo group (vehicle alone). The therapeutic efficacy was evaluated in terms of severity of dermatitis, epidermal hypertrophy, accumulation and degranulation of mast cells and infiltrated CD3+ T cells into the dermis after 4 weeks of treatment. Biweekly and daily betamethasone treatments had little effect, confirming that the dermatitis was steroid-resistant. In the FTY720 and biweekly combination groups, the dermatitis showed no marked improvement. In the daily combination group, the dermatitis was significantly (p<0.05, Mann-Whitney U-test) improved as compared with the FTY720 group, biweekly and daily betamethasone groups and placebo group. Further, epidermal hypertrophy and accumulation of mast cells were suppressed. Therefore, combination therapy with FTY720 and daily betamethasone ointment is a promising candidate for treatment of steroid-resistant atopic dermatitis.

Innate immunity in atopic dermatitis

Atopic dermatitis (AD) is a clinically defined, highly pruritic, chronic inflammatory skin disease. In AD patients, the combination of a genetic predisposition for skin barrier dysfunction and dysfunctional innate and adaptive immune responses leads to a higher frequency of bacterial and viral skin infections. The innate immune system quickly mobilizes an unspecific, standardized first-line defense against different pathogens. Defects in this system lead to barrier dysfunction which results in increased protein allergen penetration through the epidermis and predisposes to secondary skin infections. Two loss-of-function mutations in the epidermal filaggrin gene are associated with AD. Also, inducible endogenous antibiotics such as the antimicrobial peptides cathelicidin and the beta-defensins may show defective function in lesional AD skin. Eczema herpeticum is a disseminated viral infection almost exclusively diagnosed in AD patients, which is based on unmasking of the viral entry receptor nectin-1, lack of cathelicidin production by keratinocytes, and depletion of Type I IFN-producing plasmacytoid dendritic cells from AD skin. Future therapeutic approaches to AD may include enhancement of impaired innate in addition to downregulation of dysfunctional adaptive immunity.

Glucocorticoid resistance in inflammatory diseases

Glucocorticoid resistance or insensitivity is a major barrier to the treatment of several common inflammatory diseases-including chronic obstructive pulmonary disease and acute respiratory distress syndrome; it is also an issue for some patients with asthma, rheumatoid arthritis, and inflammatory bowel disease. Several molecular mechanisms of glucocorticoid resistance have now been identified, including activation of mitogen-activated protein (MAP) kinase pathways by certain cytokines, excessive activation of the transcription factor activator protein 1, reduced histone deacetylase-2 (HDAC2) expression, raised macrophage migration inhibitory factor, and increased P-glycoprotein-mediated drug efflux. Patients with glucocorticoid resistance can be treated with alternative broad-spectrum anti-inflammatory treatments, such as calcineurin inhibitors and other immunomodulators, or novel anti-inflammatory treatments, such as inhibitors of phosphodiesterase 4 or nuclear factor kappaB, although these drugs are all likely to have major side-effects. An alternative treatment strategy is to reverse glucocorticoid resistance by blocking its underlying mechanisms. Some examples of this approach are inhibition of p38 MAP kinase, use of vitamin D to restore interleukin-10 response, activation of HDAC2 expression by use of theophylline, antioxidants, or phosphoinositide-3-kinase-delta inhibitors, and inhibition of macrophage migration inhibitory factor and P-glycoprotein.

Prevalence and molecular characteristics of Staphylococcus aureus isolates colonizing patients with atopic dermatitis and their close contacts in Singapore

BACKGROUND

Staphylococcus aureus colonization is an established pathogenic factor for disease flare in atopic dermatitis (AD).

OBJECTIVES

We conducted a study to investigate the colonization of S. aureus in patients with AD and their close contacts in order to evaluate the possibility of intrafamilial transmission. We sought to determine the distribution of the bacterial virulence factors and their correlation with disease severity.

METHODS

Nasal swabs and skin swabs (patients with AD only) were taken from patients with AD aged 2-21 years and their close contacts, seen at the National Skin Centre from January to March 2007. All S. aureus isolates were typed using multilocus variable-number tandem-repeat fingerprinting (MLVF) and screened for virulence factors via polymerase chain reaction (PCR) analysis. AD severity was determined by the SCORAD index.

RESULTS

A total of 34 patients with AD and 55 close contacts were recruited. Thirty-one (91%) patients were colonized with S. aureus. Twenty-five (45%) of their close contacts were also colonized, and MLVF showed a high concordance of S. aureus isolates in index patients and their close contacts. On multivariate analysis, patients with a moderate SCORAD were more likely to be colonized by enterotoxin B-positive S. aureus (P = 0.027). No virulence factor was significantly associated with a severe SCORAD.

CONCLUSIONS

The prevalence of S. aureus colonization was high among patients with AD and their close contacts. However, no predominant isolate of S. aureus was found to be associated with AD. The presence of superantigen B is possibly associated with moderate rather than severe disease in our population.

The immune system and atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease with a complex pathogenesis. It is clinically well-defined and represents one manifestation of the atopic state, along with asthma, food allergy and/or allergic rhinitis. Within the last several decades, there has been much evidence to support the contribution of immune mechanisms in the pathogenesis of AD. It has also been documented that the prevalence of all atopic disease, including AD, has been increasing, although the environmental factors that may be contributing to this increase are not clearly defined. A better understanding of the underlying immunopathogenesis of AD should aid in better clinical management and development of new treatment options.