Is/are pattern recognition receptor(s) for Staphylococcus aureus defective in atopic dermatitis?

Dupilumab provides favourable long-term safety and efficacy in children aged ≥ 6 to < 12 years with uncontrolled severe atopic dermatitis: results from an open-label phase IIa study and subsequent phase III open-label extension study

Background

Children aged ≥ 6 to < 12 years with severe atopic dermatitis (AD) have limited treatment options. In a 16‐week, randomized, placebo‐controlled, phase III trial in children, dupilumab, a monoclonal antibody inhibiting interleukin (IL)‐4/IL‐13 signalling, significantly improved signs and symptoms with acceptable safety; longer‐term safety and efficacy data are lacking.

Objectives

To report the pharmacokinetic profile and long‐term safety and efficacy of dupilumab in children (aged ≥ 6 to < 12 years) with severe AD.

Methods

Children (aged ≥ 6 to < 12 years) with severe AD were enrolled in a global, multicentre, phase IIa, open‐label, ascending‐dose, sequential cohort study and subsequent open‐label extension (OLE) study. Patients received single‐dose dupilumab 2 or 4 mg kg⁻¹ followed by 8‐week pharmacokinetic sampling, then 2 or 4 mg kg⁻¹ weekly for 4 weeks (phase IIa), followed by the same weekly regimen (OLE). Primary endpoints were dupilumab concentration–time profile and treatment‐emergent adverse events (TEAEs); secondary assessments included Eczema Area and Severity Index (EASI) and Peak Pruritus Numeric Rating Scale (PP‐NRS) score.

Results

Of 38 children enrolled, 37 completed phase IIa and 33 continued to the OLE. Nonlinear, target‐mediated pharmacokinetics characterized dupilumab concentrations (week 24–48 mean serum concentrations: 2 mg kg⁻¹, 61–77 mg L⁻¹; 4 mg kg⁻¹, 143–181 mg L⁻¹). TEAEs were mostly mild to moderate and transient; none led to treatment discontinuation. The most commonly reported TEAEs were nasopharyngitis (2 mg kg⁻¹, 47%; 4 mg kg⁻¹, 56%) and AD exacerbation (29% and 13%, respectively). Single‐dose dupilumab rapidly improved AD with further improvements through week 52. Mean EASI and PP‐NRS improved by −37%/−33% and −17%/−20% at week 2 (phase IIa) and −92%/−84% and −70%/−58% at week 52 (OLE), respectively.

Conclusions

These safety and efficacy results support the use of dupilumab as a continuous long‐term treatment for children aged ≥ 6 to < 12 years with severe AD.

What is already known about this topic?

Severe atopic dermatitis (AD) has a marked negative impact on patient quality of life and can cause financial burden owing to a lack of effective treatments.

Dupilumab significantly improved signs and symptoms of AD with an acceptable safety profile in a 16‐week randomized, double‐blind, placebo‐controlled phase III study in children aged ≥ 6 to < 12 years with severe AD.

What does this study add?

This study extends information on the safety, efficacy and pharmacokinetic profile of dupilumab treatment for up to 52 weeks in children aged ≥ 6 to < 12 years with severe AD.

The results support the use of dupilumab as a continuous long‐term treatment for children aged ≥ 6 to < 12 years with severe AD.

Linked Comment: Sibbald. Br J Dermatol 2021; 184:792–793.

Staphylococcus aureus modulation of innate immune responses through Toll-like (TLR), (NOD)-like (NLR) and C-type lectin (CLR) receptors

Early recognition of pathogens by the innate immune system is crucial for bacterial clearance. Many pattern recognition receptors (PRRs) such as Toll-like (TLRs) and (NOD)-like (NLRs) receptors have been implicated in initial sensing of bacterial components. The intracellular signaling cascades triggered by these receptors result in transcriptional upregulation of inflammatory pathways. Although this step is crucial for bacterial elimination, it is also associated with the potential for substantial immunopathology, which underscores the need for tight control of inflammatory responses. The leading human bacterial pathogen Staphylococcus aureus expresses over 100 virulence factors that exert numerous effects upon host cells. In this manner, the pathogen seeks to avoid host recognition or perturb PRR-induced innate immune responses to allow optimal survival in the host. These immune system interactions may result in enhanced bacterial proliferation but also provoke systemic cytokine responses associated with sepsis. This review summarizes recent findings on the various mechanisms applied by S. aureus to modulate or interfere with inflammatory responses through PRRs. Detailed understanding of these complex interactions can provide new insights toward future immune-stimulatory therapeutics against infection or immunomodulatory therapeutics to suppress or correct dysregulated inflammation.

Th2 Cytokines and Atopic Dermatitis

Atopic dermatitis (AD), a chronic relapsing inflammatory skin disease, is increasing in prevalence around the world. Intensive research is ongoing to understand the mechanisms involved in the development of AD and offer new treatment options for patients suffering from AD. In this review, we highlight the importance of allergic Th2 responses in the development of the disease and summarize relevant literature, including genetic studies, studies of human skin and mechanistic studies on keratinocytes and mouse models of AD. We discuss the importance of the skin barrier and review recent findings on the pro-Th2 cytokines TSLP, IL-25, and IL-33, notably their ability to polarize dendritic cells and promote Th2 responses. After a brief update on the contribution of different T-cell subsets to AD, we focus on Th2 cells and the respective contributions of each of the Th2 cytokines (IL-4, IL-13, IL-5, IL-31, and IL-10) to AD. We conclude with a brief discussion of the current gaps in our knowledge and technical limitations.

Functional effects of interleukin 31 in human primary keratinocytes

BACKGROUND

Interleukin (IL)-31 is a T-cell cytokine acting through a heterodimeric receptor composed of IL-31RA and OSMR which is expressed on epithelial cells including keratinocytes. A major function of IL-31 in atopic dermatitis (AD) is the induction of pruritus in the skin. Inflammatory effects of IL-31 in human primary keratinocytes (HPKs) still remain unclear. We investigated expression, regulation of the IL-31 receptor as well as functions of IL-31 in HPKs.

METHODS

Human primary keratinocytes were stimulated with TLR-2 ligands (Pam3Cys, lipoteichoic acid and peptidoglycan), or Th1 and Th2 associated cytokines (IFN-γ and IL-4), respectively. IL-31R expression and regulation as well as functional effects of IL-31 stimulation were then investigated at both the mRNA and protein level and compared with HPKs from patients with AD. The STAT signalling pathway and TLR-2 expression were investigated using Western blot and Immunohistochemical stainings, respectively.

RESULTS

Pam3Cys or IFN-γ significantly up-regulated IL-31RA and OSMR expression. IL-31 activated STAT-3 phosphorylation in HPKs which was augmented after preactivation with Pam3Cys or IFN-γ. IL-31 enhanced the secretion of CCL2 after up-regulation of the receptor with Pam3Cys or IFN-γ. However, this was not observed in keratinocytes from AD patients where an impaired TLR-2 expression was found.

CONCLUSIONS

Together, our findings show a functional role of IL-31 in HPKs and provide a new link between TLR-2 ligands and IL-31 which might be dysregulated in AD. Altered function of IL-31 may have implications for cutaneous inflammation in eczema where skin colonization with Staphylococcus aureus and dysregulation of TLR-2 have been described.

The infectious aspects of atopic dermatitis

Atopic dermatitis is characterized by Staphylococcus aureus colonization and recurrent skin infections. In addition to an increased risk of invasive infections by herpes simplex or vaccinia viruses, there is ample evidence that microbial pathogens, particularly S aureus and fungi, contribute to the cutaneous inflammation of atopic dermatitis. The authors describe recent developments in the pathogenesis of atopic dermatitis in relation to the role of microbial pathogens. Understanding how microbial pathogens interact or evade the cutaneous immunity of atopic dermatitis may be crucial in preventing infections or cutaneous inflammation in this disease.

Impaired TLR-2 expression and TLR-2-mediated cytokine secretion in macrophages from patients with atopic dermatitis

BACKGROUND

In many patients with atopic dermatitis (AD), the disease is complicated by their enhanced susceptibility to bacterial skin infections, especially with Staphylococcus aureus. The pattern recognition receptor toll-like receptor (TLR)-2 recognizes components of S. aureus, for example, lipoteichoic acid (LTA) and peptidoglycan (PGN) and, therefore, might be crucial in the pathogenesis and flare-ups of AD.

OBJECTIVE

To investigate TLR-2 expression and cytokine secretion in macrophages from patients with AD compared to healthy controls upon TLR-2 stimulation with PGN, LTA and Pam3Cys.

METHODS

Macrophages were cultivated from highly purified peripheral blood monocytes of AD patients and nonatopic healthy controls and stimulated with PGN, LTA and Pam3Cys in a time and dose-dependent manner. Afterwards, TLR-2 expression and cytokine secretion were measured on protein and mRNA level. TLR-1 and TLR-6 expression were investigated on the mRNA level. Immunohistochemical stainings from punch biopsies were performed to investigate TLR-2 expression in skin macrophages.

RESULTS

We could clearly show that macrophages from patients with AD expressed significantly less TLR-2, whereas the expression pattern of TLR-1 and TLR-6 were not altered. Macrophages had a reduced capacity to produce pro-inflammatory cytokines such as IL-6, IL-8 and IL-1beta after stimulation with TLR-2 ligands.

CONCLUSION

Our findings clearly show an impaired TLR-2 expression and functional differences of TLR-2-mediated effects on macrophages of AD patients compared to healthy controls which might contribute to the enhanced susceptibility to skin infections with S. aureus in AD.

Emerging drugs for atopic dermatitis

Atopic dermatitis (AD) is the most common chronic inflammatory skin disease, affecting 10-20% of children and 2% of adults worldwide. Preventive treatment of AD consists of daily skin hydration and emollient therapy; but the majority of patients still require symptomatic treatment with topical corticosteroids and/or topical calcineurin inhibitors, both of which may be associated with potential long-term side effects. With increasing evidence supporting the role of skin barrier defects in the pathogenesis of AD, there is also a parallel increase in medications that claim to assist barrier repair. The current review discusses some exciting results with these medications, as well as the challenges that lie ahead of them. While barrier repair treatments offer some promise, there continues to be a need for safer anti-inflammatory medications. Some of these medications under investigation are phosphodiesterase-4 inhibitors, urocanic acid oxidation products and IL-4/IL-13 receptor blockers. The review also discusses anti-staphylococcal treatments including nanocrystalline silver cream, silver and antimicrobial-coated fabrics, and anti-itch treatments including mu-opiod receptor antagonists, chymase inhibitors and cannabinoid receptor agonists. These medications may become an integral part of AD therapy.

Dysregulation of toll-like receptor-2 (TLR-2)-induced effects in monocytes from patients with atopic dermatitis: impact of the TLR-2 R753Q polymorphism

BACKGROUND

Atopic dermatitis (AD) is often complicated by an enhanced susceptibility to bacterial skin infections, especially with Staphylococcus aureus. Toll-like receptors (TLR), especially TLR-2 recognizes cell wall components of S. aureus, e.g. lipoteichoic acid (LTA) and peptidoglycan (PGN). A heterozygous TLR-2 R753Q polymorphism occurs in a frequency of 11.5% in adult AD patients and has been shown to be associated with a severe phenotype of AD.

METHODS

The aim of this study was to investigate the impact of TLR-2 agonists (LTA, PGN and Pam3Cys) on cytokine production in human monocytes from AD patients with the TLR-2 R753Q polymorphism compared with that of AD patients with 'wild type' TLR-2 and control individuals to elucidate the functional role of the TLR-2 R753Q polymorphism.

RESULTS

Monocytes from AD patients with the TLR-2 R753Q mutation produced significantly more IL-6 and IL-12 compared with that of AD patients with nonmutated TLR-2 upon stimulation with TLR-2 agonists.

CONCLUSION

We show for the first time functional differences in TLR-2 responsiveness of monocytes from AD patients with the TLR-2 R753Q mutation compared with wild type AD patients in a ligand-dependent manner.

CLINICAL IMPLICATION

Our data support the emerging concept that AD patients have a dysbalance in innate and acquired immunity. TLR-2 may be essential in the pathogenesis and maintenance of AD and may be involved in the enhanced susceptibility to skin infections with S. aureus and in a higher inflammatory response in patients with AD carrying the TLR-2 polymorphism.

Implant infection caused by dermatitis: a report of two cases

We report 2 cases of implant infection with Staphylococcus aureus associated with dermatitis. In both cases, the skin at the surgical site was normal and full antiseptic measures were taken. One patient had a history of chronic asteatotic eczema complicated by cellulitis; the other had generalised exfoliative dermatitis with an atopic aetiology. Dermatitis at sites remote from the operative site may be a contributing factor in implant infection.