الفهرس 
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Abstract
Introduction: Psoriasis is a genetic disease of dysregulated inflammation that affects approximately 2-3 % of the world’s population (Habif, 2016). It is a chronic inflammatory disease of the skin; characterized by epidermal hyperplasia, dermal angiogenesis, infiltration of activated T cells, and increased cytokine levels (Hueber and McInnes, 2007). One of these cytokines, interleukin-15 (IL-15), is a proinflammatory cytokine and its expression is upregulated under inflammatory conditions (Fehniger and Caligiuri, 2001). Antibody-mediated blockade of IL-15 is an effective inhibitor of autoimmunity (Norris, 2013). Interleukin-15 is secreted by mononuclear phagocytes and exerts its biological effects using signaling via the interleukin-15 receptor (IL-15R)α, β and γc chains (Giri et al., 1995). It acts early in the inflammatory response and induces the production of other cytokines such as tumor necrosis factor-α (TNF-α), interferon-gamma (IFN-γ), and IL-17 (McInnes et al., 1997) which are all upregulated in psoriatic lesions. Furthermore, IL-15 amplifies inflammation by the recruitment and activation of T cells (Grabstein et al., 1994) and also induces angiogenesis (Angiolillo et al., 1997). IL-15 plays a pivotal role in the development, survival, and functions of natural killer (NK) cells (Carson et al., 1997), and has documented antiapoptotic effects (Rückert et al., 2000). Dysregulation of IL-15 expression was reported in patients with rheumatoid arthritis, inflammatory bowel diseases, coeliac disease and psoriasis (Baslund et al., 2005). A significant upregulation of IL-15 and its receptor have been shown in psoriatic lesions (Nickoloff, 2000; Rückert et al., 2000). Villadsen et al. (2003) observed resolution of psoriatic lesions with a downregulation of hyperkeratosis, parakeratosis, and inflammatory cell proliferation when anti-IL-15 antibodies were injected into immunocompromised mice with xenografted psoriatic skin. Study hypothesis: serum level of IL-15 is elevated in psoriasis vulgaris (might play a role in this autoimmune disease). The Aim of this study: The aim of this work was to assess IL-15 serum levels in patients with psoriasis vulgaris; and to correlate its levels with disease severity and activity. Materials and methods: 3 groups of subjects who reside in Dakahlia governorate: groupA-30 patients suffering from active psoriasis vulgaris, groupB-30 patients with stable psoriasis vulgaris and groupC-60 age- and sex-matched healthy controls. Results: The current revealed that: In this study, there were no statistically significant differences in patients demographics when compared to the control group. The mean ± SD PASI score in patients with active psoriasis vulgaris (20.93 ± 4.76) was significantly higher than that in stable cases (10.82 ± 2.53). Serum IL-15 showed statistically significant higher median value among psoriasis patients as compared to control group. The level of serum IL-15 in active psoriasis (median, 82.77 pg/ml; range, 67.30 – 142.98) was significantly higher than its level in inactive psoriasis (53.24 pg/ml; range, 40.89- 68.23). In addition, there was statistically significant positive correlation between serum IL-15 level in all studied psoriasis cases and each of BMI and PASI score; while there was no significant correlation between the level of IL-15 and each of age and duration of disease. Receiver operating characteristics (ROC) curve detected the validity of serum IL-15 in differentiating psoriasis patients from controls. The best cut-off point for IL-15 was determined to be ≥ 36.12 pg ∕ ml, which was able to predict psoriasis with 100 % sensitivity and 100 % specificity, and accuracy, was 100 %. ROC curve of IL-15 was also conducted to evaluate the sensitivity and specificity of serum IL-15 as a diagnostic index for discrimination between active and stable psoriasis cases. The AUC-ROC of IL-15 was excellent (0.996). At best cut-off value of ≥ 67.7 pg / ml, sensitivity was 96.7 %, specificity was 93.3%, and accuracy was 95 %. Serum level of IL-15 was a statistically significant predictor of PASI score with 97.6 % of PASI score can be predicted by serum IL-15. Conclusion: Based on the results of this study that revealed a higher serum concentration of IL-15 along with correlation with PASI score in psoriasis patients, it may be concluded that this cytokine has a potential pathogenic role in the development of psoriasis vulgaris in Egyptian patients. Furthermore, serum levels of IL-15, which correlated with the clinical severity and activity of psoriasis, may be objective parameters of successful treatment and may be used in the followup. The development of new therapeutical strategies targeting IL-15 may reduce the next events of inflammatory reactions and prevent the psoriasis exacerbation and systemic complications. It is hoped that in the near future, new investigations on a larger study population will bring more details and lead to invention of new therapeutic regimens.