Pruritus in allergy and immunology

CXCL12/CXCR4 signaling induced itch and pain sensation in a murine model of allergic contact dermatitis

Allergic contact dermatitis is a skin inflammatory disease manifested with itch and pain symptom around the inflamed area. Chemokines such as CXCL12 are involved in the pathophysiology of allergic contact dermatitis, but little has been known about the effect of CXCL12/CXCR4 signaling for nociceptive sensation accompanying allergic contact dermatitis. Our study showed that CXCL12 and CXCR4 were upregulated in trigeminal ganglion with the progression of allergic contact dermatitis through western blotting and immunofluorescence. CXCL12 and CXCR4 were mainly upregulated in small-diameter neurons, which were co-localized with nociceptive markers in trigeminal ganglion. CXCR4 and CXCL12 were also expressed in trigeminal ganglion neurons retrograded from the skin lesion. Intradermal injection of CXCL12 enhanced the itch- and pain-like behavior which could be relieved by AMD3100, a CXCR4 antagonist, without changes of mast cells. Our findings suggested that blockade of CXCL12/CXCR4 signaling pathway might be beneficial to relieve itch and pain sensation accompanying allergic contact dermatitis.

Anti-Allergic Effects of the Subcritical Water Extract Powder of Citrus unshiu in Mouse and Guinea Pig Models

We evaluated the effects of unripe mandarin orange (Citrus unshiu) extract powder (unripe mandarin extract powder [UMEP]) treated with subcritical water on allergic diseases by using animal models. High performance liquid chromatography (HPLC) analysis revealed that subcritical water is a more effective solvent than alcohol and hot water, as it quickly extracted approximately 90% of the functional compounds narirutin (1) and hesperidin (2) from whole fruits. Repeated oral administration of UMEP significantly reversed the peripheral blood flow decline observed during the promotion of allergies after sensitization with the antigen, hen egg-white lysozyme (HEL). UMEP also significantly inhibited compound 48/80-induced scratching behavior in HEL-sensitized mice, which are more sensitive to itching stimuli than are normal mice, without suppressing locomotor activity. In addition, repeated oral administration of UMEP in ovalbumin-challenged guinea pigs significantly suppressed the late phase of nasal airway resistance. This study provides evidence that the subcritical water extract powder of unripe C. unshiu fruit is an effective anti-allergic functional food.

Chemogenetic activation of central gastrin-releasing peptide-expressing neurons elicits itch-related scratching behavior in male and female mice

Several lines of evidence have clarified that the key transmission pathways of itching sensation travel from the periphery to the central nervous system (CNS). Despite the functional significance of gastrin-releasing peptide (GRP) and its cognate receptor in the itch processing mechanism in the spinal dorsal horn (SDH), the roles of GRP-expressing (GRP+ ) neurons in different regions remain unclear. This study aimed to determine whether GRP+ neurons in the CNS directly modulated itch processing. To specifically activate spinal and supraspinal GRP neurons by the designer receptors exclusively activated by designer drugs (DREADDs) system, CAG-LSL-Gq-DREADD mice were crossed with GRP-Cre mice, resulting in the development of GRP-hM3Dq mice. Immunohistochemistry showed that hM3Dq was highly expressed in the SDH and brainstem closely related to sensory processing. The intraperitoneal, intrathecal, or intracerebroventricular administration of clozapine-N-oxide, an agonist of hM3Dq, strongly elicited dermatome-dependent itch-related scratching behavior, but did not change pain sensitivity. Importantly, GRP-Gq-DREADD-mediated scratching behavior in GRP-hM3Dq mice was not affected by the ablation of transient receptor potential vanilloid 1+ sensory C-fibers, and it was also observed to a similar degree under chronic itch conditions. Furthermore, there were no significant sex differences in the scratching behavior elicited by GRP-Gq-DREADD, suggesting that itch-dominant roles of central GRP+ neurons might be common in both sexes, at least under normal physiological conditions. These novel findings not only contribute to understanding the functional roles of central GRP+ neurons further, but also propose the development of future effective therapeutics for intractable itching.

Mast Cells in the Skin: Defenders of Integrity or Offenders in Inflammation?

Mast cells (MCs) are best-known as key effector cells of immediate-type allergic reactions that may even culminate in life-threatening anaphylactic shock syndromes. However, strategically positioned at the host–environment interfaces and equipped with a plethora of receptors, MCs also play an important role in the first-line defense against pathogens. Their main characteristic, the huge amount of preformed proinflammatory mediators embedded in secretory granules, allows for a rapid response and initiation of further immune effector cell recruitment. The same mechanism, however, may account for detrimental overshooting responses. MCs are not only detrimental in MC-driven diseases but also responsible for disease exacerbation in other inflammatory disorders. Focusing on the skin as the largest immune organ, we herein review both beneficial and detrimental functions of skin MCs, from skin barrier integrity via host defense mechanisms to MC-driven inflammatory skin disorders. Moreover, we emphasize the importance of IgE-independent pathways of MC activation and their role in sustained chronic skin inflammation and disease exacerbation.

IL-31 Inhibition as a Therapeutic Approach for the Management of Chronic Pruritic Dermatoses

Chronic pruritus is a debilitating symptom with limited treatment options. Identifying molecular targets underlying chronic pruritic dermatoses is essential for the development of novel, targeted therapies. IL-31 is an important mediator of itch by integrating dermatologic, neural, and immune systems. IL-31 helps induce and maintain chronic pruritus via both indirect stimulation of inflammatory cells and through direct neural sensitization. IL-31 is overexpressed in various chronic pruritic skin conditions, and exogenous IL-31 induces itch and scratching behavior. Studies have demonstrated that IL-31R and IL-31 antagonism significantly reduces itch in patients with atopic dermatitis and prurigo nodularis, two extremely pruritic skin conditions. Emerging evidence, including recent phase II clinical trials of IL-31R antagonists, demonstrates that IL-31 plays an important role in itch signaling. Additional studies are ongoing to evaluate IL-31R and IL-31 antagonism as treatments of chronic pruritus.

Cutaneous Neuroimmune Interactions in Peripheral Neuropathic Pain States

Bidirectional interplay between the peripheral immune and nervous systems plays a crucial role in maintaining homeostasis and responding to noxious stimuli. This crosstalk is facilitated by a variety of cytokines, inflammatory mediators and neuropeptides. Dysregulation of this delicate physiological balance is implicated in the pathological mechanisms of various skin disorders and peripheral neuropathies. The skin is a highly complex biological structure within which peripheral sensory nerve terminals and immune cells colocalise. Herein, we provide an overview of the sensory innervation of the skin and immune cells resident to the skin. We discuss modulation of cutaneous immune response by sensory neurons and their mediators (e.g., nociceptor-derived neuropeptides), and sensory neuron regulation by cutaneous immune cells (e.g., nociceptor sensitization by immune-derived mediators). In particular, we discuss recent findings concerning neuroimmune communication in skin infections, psoriasis, allergic contact dermatitis and atopic dermatitis. We then summarize evidence of neuroimmune mechanisms in the skin in the context of peripheral neuropathic pain states, including chemotherapy-induced peripheral neuropathy, diabetic polyneuropathy, post-herpetic neuralgia, HIV-induced neuropathy, as well as entrapment and traumatic neuropathies. Finally, we highlight the future promise of emerging therapies associated with skin neuroimmune crosstalk in neuropathic pain.

Interleukin-31 as a Clinical Target for Pruritus Treatment

In recent years, the published literature has suggested the key involvement of the cytokine interleukin-31 (IL-31) in the symptomatology of pruritus, and both IL-31 and its receptor have become potential therapeutic targets for a range of pruritic diseases. Elevated levels of IL-31 or its receptor have been reported in the tissue or serum of patients with pruritic skin diseases, such as atopic dermatitis, prurigo nodularis, and psoriasis. Pruritus places a heavy burden on patients, and can have a negative impact on daily life, sleep, and mental health. Since current anti-pruritic treatments are often ineffective, affected patients are in urgent need of new therapies. As a result, drug development targeting the IL-31 pathway is evolving rapidly. To date, only nemolizumab, a humanized monoclonal antibody targeting the IL-31 receptor, has successfully completed late-stage clinical studies. This article will highlight our current clinical understanding of the role of IL-31 in pruritic disease, and explore recent progress in drug development as well as the anticipated future advances in this field.

Appearance of Acute Inflammatory State Indicates Improvement in Atopic Dermatitis Cases Under Classical Homeopathic Treatment: A Case Series

The Continuum theory and the Levels of Health theory propound the idea that return of efficient acute inflammation (high fever) heralds true improvement in chronic inflammatory states. We present 6 cases of atopic dermatitis (AD), which had stability in their improvement for 1 year or more, under classical homeopathy. The cases were retrospectively assessed with selected based on the Hanifin Rajka atopic dermatitis diagnostic criteria and the follow ups evaluated according to changes on SCORing Atopic Dermatitis scale (SCORAD) scale. The pictures are presented as evidence. Modified Naranjo Criteria for assessing causal attribution of clinical outcome to homeopathic intervention was used to assess the effect of homeopathy in these cases. All the cases improved and stabilised with complete skin clearance (those that relapsed within 1 year were not included). These patients had not suffered high fevers/acute inflammatory diseases since onset/aggravation of AD. Five of the 6 cases developed acute inflammatory diseases as the chronic condition improved. The last case showed return of an old, lesser pathology. The control cases – which were selected for non-improvement under classical homeopathy also showed remarkable skin clearance when there was appearance of acute inflammatory states. In this study, there is a mutually exclusive relationship between efficient acute inflammation and chronic inflammation, which is in accordance with the 2 theories considered here. Further scientific studies are necessary to establish the phenomenon at tissue level.

Mast Cell-Specific MRGPRX2: a Key Modulator of Neuro-Immune Interaction in Allergic Diseases

PURPOSE OF REVIEW

Atopic dermatitis (AD) and allergic asthma are complex disorders with significant public health burden. This review provides an overview of the recent developments on Mas-related G protein-coupled receptor-X2 (MRGPRX2; mouse counterpart MrgprB2) as a potential candidate to target neuro-immune interaction in AD and allergic asthma.

RECENT FINDINGS

Domestic allergens directly activate sensory neurons to release substance P (SP), which induces mast cell degranulation via MrgprB2 and drives type 2 skin inflammation in AD. MRGPRX2 expression is upregulated in human lung mast cells and serum of asthmatic patients. Both SP and hemokinin-1 (HK-1 generated from macrophages, bronchial cells, and mast cells) cause degranulation of human mast cells via MRGPRX2. MrgprB2 contributes to mast cell-nerve interaction in the pathogenesis of AD. Furthermore, asthma severity is associated with increased MRGPRX2 expression in mast cells. Thus, MRGPRX2 could serve as a novel target for modulating AD and asthma.

Itch: A Paradigm of Neuroimmune Crosstalk

Although the medical definition of itch has been in existence for 360 years, only in the last 20 years have we begun to understand the basic mechanisms that underlie this unique sensation. Therapeutics that specifically target chronic itch as a pathologic entity are currently still not available. Recent seminal advances in itch circuitry within the nervous system have intersected with discoveries in immunology in unexpected ways to rapidly inform emerging treatment strategies. The current review aims to introduce these basic concepts in itch biology and highlight how distinct immunologic pathways integrate with recently identified itch-sensory circuits in the nervous system to inform a major new paradigm of neuroimmunology and therapeutic development for chronic itch.

Atopic dermatitis

Atopic dermatitis (AD) is a common inflammatory skin disease, clinically characterized by recurrent eczematous lesions and intense itching, leading to excoriations and susceptibility to cutaneous infections. Although it is considered a pediatric disorder, mainly starting in infancy, it is also very common in adults. Etiology of AD is complex and multifactorial: interaction between genetic susceptibility and environment, but also cutaneous barrier impairment, change in microbiome composition and innate and adaptive immune dysregulation are the main factors involved in the pathogenesis of the disease. Originally, the disorder was considered mediated by an imbalance towards a T-helper 2 response and excessive IgE production to allergens, but now it is recognized as a lifelong disposition with variable clinical expressivity, where dysfunctions of the epidermal barrier, immune system and microbiome play a central role. AD leads to a substantial psycho-social burden on patients and their relatives and increases the risk of other allergic and non allergic disorders. The real economic impact of AD is difficult to measure due to the broad spectrum of disease severity and the multiple direct and indirect costs, but the overall medical expenses seem to be very high and similar to those of other diseases such as diabetes. Currently, a multiple therapeutic approach is aimed only at improving the skin state, reducing itching and keeping a stable condition. New safety and curative treatments may be developed only after enhancing our understanding on the pathogenesis of AD and the heterogeneity of its clinical manifestations. (www.actabiomedica.it)

Atopic dermatitis

Atopic dermatitis is a common inflammatory skin disorder characterised by recurrent eczematous lesions and intense itch. The disorder affects people of all ages and ethnicities, has a substantial psychosocial impact on patients and relatives, and is the leading cause of the global burden from skin disease. Atopic dermatitis is associated with increased risk of multiple comorbidities, including food allergy, asthma, allergic rhinitis, and mental health disorders. The pathophysiology is complex and involves a strong genetic predisposition, epidermal dysfunction, and T-cell driven inflammation. Although type-2 mechanisms are dominant, there is increasing evidence that the disorder involves multiple immune pathways. Currently, there is no cure, but increasing numbers of innovative and targeted therapies hold promise for achieving disease control, including in patients with recalcitrant disease. We summarise and discuss advances in our understanding of the disease and their implications for prevention, management, and future research.

Emerging treatments for atopic dermatitis

Increasing information on the pathophysiology of atopic dermatitis (AD), accumulating data on cellular and molecular pathways in immunological reactions and inflammation, and the expansion of biotechnology and pharmacology have collectively contributed to the development of new pharmacological agents for AD. Novel pharmaceutical agents, including biologics targeting cytokines, which play pathogenetic roles in AD, for example, interleukin (IL)-4, IL-13, IL-31 and IL-22, Janus kinase inhibitors, phosphodiesterase 4 inhibitors and histamine H₄ receptor antagonists, have been approved or are being developed. These agents are expected to be effective in AD patients with skin signs and/or symptoms that are refractory to conventional treatments. The development of novel drugs will accompany the use of predictive biomarkers for each agent in order to optimize treatment in each patient. Convenient tools that support self-decision-making by patients to reflect their preferences, which will increase treatment satisfaction and adherence, are also anticipated.