Fry Lionel, Baker Barbara S, Powles Anne V, Engstrand Lars
Department of Medicine, Imperial College, London, UK.
Exp Dermatol. 2015 Apr;24(4):241-4. doi: 10.1111/exd.12572. Epub 2014 Nov 18.
The concept that psoriasis is an autoimmune disease needs to be questioned. The autoimmune label has been based on molecular mimicry between streptococcal and keratin proteins and the existence of homologous peptides between these proteins. However, it is only peripheral blood CD8, and not CD4, T lymphocytes that respond to the homologous peptides. This ignores the fact that it is CD4 T cells which are necessary to initiate psoriasis. Recent studies on skin bacterial microbiota have found a variety of bacteria in both normal skin and psoriatic lesions. In biopsy specimens, the most common phylum was Firmicutes and the most common genus streptococcus in both psoriasis and normal skin. The innate immune system is activated in psoriasis, and recent genetic findings have shown the majority of susceptibility loci are associated with innate immunity. There is a known clinical relationship between both Crohn's disease (CD) and periodontitis, and psoriasis, and patients with psoriasis share mutations in some innate immunity genes with individuals with CD. It is now accepted that CD is due to a breakdown of immune tolerance (dysbiosis) to bacteria in the intestine. These findings suggest that psoriasis is initiated by an abnormal response to bacteria in the skin due to genetic factors.
银屑病是一种自身免疫性疾病这一概念需要受到质疑。自身免疫这一标签基于链球菌蛋白和角蛋白之间的分子模拟以及这些蛋白之间同源肽的存在。然而，对同源肽产生反应的只是外周血CD8 T淋巴细胞，而非CD4 T淋巴细胞。这忽略了一个事实，即启动银屑病需要CD4 T细胞。近期关于皮肤细菌微生物群的研究发现，正常皮肤和银屑病皮损中都存在多种细菌。在活检标本中，银屑病和正常皮肤中最常见的菌门都是厚壁菌门，最常见的菌属都是链球菌属。银屑病中固有免疫系统被激活，近期的遗传学研究结果表明，大多数易感基因座都与固有免疫相关。克罗恩病（CD）、牙周炎和银屑病之间存在已知的临床关联，银屑病患者与CD患者在一些固有免疫基因上存在共同突变。现在人们认为，CD是由于对肠道细菌的免疫耐受（生态失调）遭到破坏所致。这些研究结果表明，银屑病是由遗传因素导致的对皮肤细菌的异常反应引发的。
