| BackgroudAtopic dermatitis (AD) is a chronically relapsing inflammatory skin disease with a genetic background. Pruritus is an essential feature of AD. Itching-scratch cycle plays an important role in aggravating and maintaining skin inflammation in AD. A principal purpose on treatment for AD is to control pruritus. The studies of pruritus of AD involve in multiple factors, e.g. cutaneous sensory nerve, neuropeptide, neurotrophins, inflammatory cells and cytokines. However, the mechanism of AD pruritus is still not fully understood.Interleukin-31(IL-31) is a newly found four-helix bundle cytokine that is preferentially produced by T helper type2cells, and signals through a heterodimeric receptor composed of IL-31receptor A(IL-31RA)and oncostatin M receptor β(OSMRβ). Recent studies suggest that IL-31is related with the pathogenesis and pruritus in AD, but the mechanism of IL-31involving in pruritus is unknown.ObjectiveTo investigate the role of IL-31and neurotrophins in the pathogenesis of AD and their correlation with the severity with disease; to explore the probable mechanism of IL-31and NT-4in AD pruritus.Methods1. Sixty-nine children with AD defined according to the criteria of Hanifin and Rajka, and thirty-seven age matched healthy controls were recruited in this study. SCORAD of AD patients was assessed, serum levels of IL-31and NT-4in AD patients and healthy controls were measured by means of ELISA.2. An AD mice model which were sensitized and challenged on the skin with ovalbumin repeatedly was used, and analyzed lesion skin sites of mice for the expression of IL-31mRNA, IL-31receptors IL-31RA and OSMRβ, NT-4receptor TrkB, as well as serum levels of IL-31and NT-4of AD mice by means of semiquantitative real-time RT-PCR, immunohistochemisty and western blot, ELISA, respectively.Results1. The overall mean SCORAD score (±SD) was53.56±14.44for AD patients (n=69). And the SCORAD score of mild-to-moderate AD patients (SCORAD≦50) was39.78±8.92(n=27), severe AD patients (SCORAD>50) was62.42±9.48(n=42).2. We found the overall serum level of IL-31as well as mild-to-moderate AD patients were both increased statistically in AD patients compared with healthy controls (34.73±13.33vs20.89±8.90pg/ml, p<0.001and28.52±13.00pg/ml vs20.89±8.90pg/ml, p<0.05; respectively). And the serum IL-31level of severe AD patients (38.72±12.08pg/ml) was significantly increased compared to healthy controls and mild-to-moderate AD patients (p<0.001and p<0.01, respectively)2. The average of overall serum NT-4level was8.84ng/ml(1.55-45.75), and significantly higher than that of healthy controls (2.95ng/ml (0.82-21.12); p<0.01). Moreover, the serum NT-4levels of mild-to-moderate (10.61±9.17ng/ml) and severe AD patients (14.73±11.90ng/ml) were both significantly higher than heathy control (p<0.05and p<0.01, respectively).3. The IL-31serum level was correlated positively with SCORAD and NT-4serum level in AD pateints (r=0.557, p<0.001and r=0.515, p<0.001, respectively). Moreover, the serum NT-4level of severe AD patients was correlated positively with corresponding SCORAD (r=0.327, p<0.05).4. The sensitized skin sites of AD mice were developed edema and thickening at sixth week. HE analysis of sensitized skins of AD mice showed a hyperplasia of the epidermis and acanthosis in the lesion skin biopsies. The dermis was infiltrated with neutrophils, eosinophils, and lymphocytes, while normal saline (NS) control mice shew normally. It confirmed that the murine model of AD was complete.5. IL-31mRNA expression in lesion skin sites of AD mice was13.89 folds higher than NS controls (p<0.01).6. The serum IL-31level of AD mice was significantly higher than NS control (171.63±14.15vs152.15±14.19pg/ml, p<0.05). However, AD and control mice did not show statisitic difference in serum NT-4levels (115.47±16.50vs112.99±11.20pg/ml,p>0.05).7. In lesion skin sites of AD mice, IL-31RA was found to be expressed on keratinocytes, follicle cells and macrophages,OSMRβ was on keratinocytes and follicle cells, and the receptor of NT-4,TrkB, was on keratinocytes and Peripheral nerve fibers. Moreover, IL-31RA, as well as TrkB, but not OSMRβ were more pronounced in skin lesion of AD mice compared with control.Conclusion1. The serum IL-31level of AD patients was increased significantly and positive correlation with disease severity. The serum IL-31level and IL-31mRNA expression of lesion skin sites in AD mice were both eveluated significantly. Those findings furthermore comfirmed the role of IL-31in the pathogenesis of AD and IL-31could serve as a marker of disease severity in AD.2. The serum NT-4level of AD patients was increased significantly and positive correlation with serum IL-31level, suggesting that NT-4may play an important role in the pahtogenesis of AD.3. In lesion skin sites of AD mice, the receptors of IL-31,IL-31RA and OSMRβ, were found to be expressed on keratinocytes. And the receptor of NT-4,TrkB, was expressed on peripheral nerve fibers.Moreover, IL-31RA and TrkB were both more pronounced in skin lesions of AD mice. The above results hint that IL-31may involve in the pathophysiology of pruritus through activation of keratinocytes to release NT-4that integrates with TrkB expressed on peripheral nerve fibers in AD. |
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