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BACKGROUND: Prurigo nodularis (PN) is a chronic inflammatory skin disorder that is characterized by extremely itchy nodules. Proadrenomedullin N-terminal 20 (PAMP) activates mast cell degranulation via Mas-related G protein-coupled receptor X2 (MRGPRX2), which is associated with pruritus in allergic contact dermatitis. However, the mechanisms underlying the action of PAMP and MRGPRX2 in PN remain unclear.
OBJECTIVE: To determine the role of PAMP-induced mast cell activation via MRGPRX2 (mouse homologous Mrgprb2) in PN.
METHODS: The expression of PAMP and the number of MRGPRX2-expressing mast cells in the skin biopsies of patients with PN, atopic dermatitis (AD), and healthy participants were analyzed using immunohistochemistry and immunofluorescence, respectively. The biphasic response of PAMP9-20 mediated by Mrgprb2 in mouse peritoneal mast cells (PMC) was validated in vitro using qRT-PCR, ELISA, flow cytometry, and siRNA techniques.
RESULTS: PAMP expression and the number of MRGPRX2+ mast cells in lesional PN skin, but not in AD, were elevated compared to healthy skin. PAMP9-20 mediates the immediate and delayed phase responses of PMC, such as degranulation, histamine and β-hexosaminidase release, and secretion of inflammatory factors such as CCL2, TNF-α, and GM-CSF. These effects were inhibited when Mrgprb2 expression was silenced. Silencing Mrgprb2 did not affect the biphasic response of PMC that was induced by IgE-FcεRI activation.
CONCLUSIONS: The results show that PAMP mediates mouse mast cell activation via Mrgprb2, which may be involved in the pathogenesis of PN. The PAMP/ Mrgprb2 pathway, independent of classical IgE signaling, could be developed as a candidate drug target for treating PN.

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Pruritus is the most common symptom of dermatological disorders, and prurigo nodularis (PN) is notorious for intractable and severe itching. Conventional treatments often yield disappointing outcomes, significantly affecting patients\' quality of life and psychological well-being. The pathogenesis of PN is associated with a self-sustained \"itch-scratch\" vicious cycle. Recent investigations of PN-related itch have partially revealed the intricate interactions within the cutaneous neuroimmune network; however, the underlying mechanism remains undetermined. Itch mediators play a key role in pruritus amplification in PN and understanding their action mechanism will undoubtedly lead to the development of novel targeted antipruritic agents. In this review, we describe a series of pruritogens and receptors involved in mediating itching in PN, including cytokines, neuropeptides, extracellular matrix proteins, vasculogenic substances, ion channels, and intracellular signaling pathways. Moreover, we provide a prospective outlook on potential therapies based on existing findings.

BACKGROUND: Chronic prurigo (CPG) is an inflammatory skin disease. Comorbidities including dermatological, cardiovascular, and psychiatric diseases have been reported in patients with CPG; however, the evidence has not been systematically evaluated. We aim to summarize the comorbidities, discuss underlying pathogenesis, and highlight the evaluation of CPG patients.
METHODS: We performed a systematic search using PubMed, Embase, and Web of Science databases for all articles reporting possible associated diseases with CPG. Pooled random-effects odds ratios (ORs) with 95% CI were calculated.
RESULTS: A total of 17 studies were included in this systematic review. Statistically significant association (p <0.05) with CPG has been demonstrated with atopic diseases: atopic dermatitis (pooled OR, 10.91; 95% CI, 3.65-32.67), allergic rhinitis (2.66; 1.12-6.27), asthma (3.23; 1.55-6.74); infectious diseases: hepatitis B (pooled OR, 2.15; 95% CI, 1.11-4.14); endocrine diseases: diabetes (pooled OR, 4.93; 95% CI, 1.13-21.56), type 1 diabetes (2.46; 2.16-2.81), type 2 diabetes (1.89; 1.34-2.68), hyperlipoproteinemia (2.90; 1.61-5.22); cardiovascular diseases: heart failure (pooled OR, 4.13; 95% CI, 1.15-14.91), hypertension (3.17; 1.56-6.45); respiratory system diseases: chronic obstructive pulmonary disease (pooled OR, 3.19; 95% CI, 1.42-7.16); urinary system diseases: chronic kidney disease (pooled OR, 4.16; 95% CI, 1.79-9.66); digestive system disease: inflammatory bowel disease (pooled OR, 2.06; 95% CI, 1.26-3.36); and others: osteoporosis (pooled OR, 3.08; 95% CI, 1.70-5.59), thyroid disease (1.70; 1.17-2.47).
CONCLUSIONS: CPG is associated with various systemic disorders. Recognition of comorbidities is critical to the appropriate management of affected patients.

Linear IgA/IgG bullous dermatosis (LAGBD) is a rare autoimmune subepidermal bullous disorder characterized by linear deposition of concurrent IgA and IgG autoantibodies along the basement membrane zone (BMZ). The clinical features of LAGBD can be diverse, including tense blisters, erosions, erythema, crusting and mucosa involvement, while papules or nodules are generally absent. In this study, we present a unique case of LAGBD, which showed prurigo nodularis-like clinical appearance on physical examination, linear deposition of IgG and C3 along the basement membrane zone (BMZ) in direct immunofluorescence (DIF), IgA autoantibodies against the 97-kDa and 120-kDa of BP180 and IgG autoantibodies against the 97-kDa of BP180 by immunoblotting (IB), while BP180 NC16a domain, BP230, and laminin 332 were negative by enzyme-linked immunosorbent assay (ELISA). After administration of minocycline, the skin lesions improved. We performed a literature review of LAGBD cases with heterogeneous autoantibodies and found clinical presentations of most cases resemble bullous pemphigoid (BP) and linear IgA bullous disease (LABD), which is consistent with previous reported findings. We aim to increase our understanding of this disorder and to enhance the importance of applying immunoblot analyses and other serological detection tools in clinic for precise diagnosis as well as accurate treatment strategy of various autoimmune bullous dermatoses.