| Psoriasis is a chronic, inflammatory skin disease. The characteristics are recurrent localized plaques with silvery scales. The skin lesions are symmetrical and affecting limbs, trunk, scalp, nail, and joints. The pothologic findings are abnormalities in proliferation and differentiation of keratocytes, inflammatory cell infiltration and vascular changes. Psoriasis is a common disease. Based on the clinical - epidemical investigation, more and more facts demonstrate the disease has obvious differences between the ethnic groups and geographical regions. It's more common in Caucasians, less common in Asians, and rare in blacks. In our country, it affects about 0. 123 % of the population, the north is more common than south, and male is more common than female, and more common in city than countryside. In United States, the incidence is about 0. 15 to 1.5 % , and in Europe 1 to 2%. The first onset is mostly in youth or adult.The cause and pathogenesis of psoriasis is unknown. Recently, following the advance of molecular biology and immunology, many investigations confirmed the psoriasis is an inflammatory disease with abnormal immune expression and multi - gene background. The relationship on cytokines and psoriasis is the focus in the psoriasis immunology. There is significant abnormality of cytokines in psoriasis, such as the overexpression of the Th 1 cytokines - tumor necrosis factor - a and r - interferon and relative deficiency of Th 2 cytokine - interleu-kin -10 and so on.Tumor necrosis factor - a is a potent cytokine with a wide range of pro -inflammatory activities. It has been implicated in many diseases and play an important role in inflammatory diseases and has an central part in psoriasis pathogenesis. It can induce the expression of intercellular adhesion molecule(1CAM) on keratocytes and vascular endothelium and offering the adherent site for neutrophiles and lymphocytes. It also can induced in keratocytes and fibro-blastes the production of interleukin 8 (IL - 8) that acts as a chemotactic factor for neutrophiles, and stimulating factor for proliferation of keratocytes, and leads the infiltration and activation of inlfammatory cells and the release of inflammatory mediators. Thus it plays an important role. Tumor necrosis factor is the prod-uct of tumor necrosis factor gene that was stimulated by some stimuli on mononu-clear cells, macrophages and T lymphocytes. The tumor necrosis factor - a gene located within the class III region of the major histocompatibility complex ( MHC) on chromosome 6p21, ?250 kilobases centromeric of the HLA - B locus and 350 kilobases telomeric of HLA - DR. Tumor necrosis factor - a gene is polymorphic. Some polymorphisms in the tumor necrosis factor region have been described, including five microsatellites and several point mutations, particularly in the promoter region. The mark of the polymorphisms in the gene is the base changes in the region. The polymorphisms of the gene are associated with the high level of the cytokine. In view of the biological effects and the gene location, it has been speculated that the polymorphism within this locus might contribute the susceptibility to and /or severity in some autoimmunity diseases, infections and neoplasms, especially the diseases that are associated with HLA locus. Many studies have focus on the association between the HLA loci and psoriasis. Different studies had different conclusions and the conclusions vary among different ethnic and different regions. The results shown that the psoriasis vul-garis in Chinese is associated with the HLA - Al, B13, B17, Cw6 and DR7.Many studies have shown that the level of tumor necrosis factor - a is higher in serum and overexpressed in psoriatic skin. Tumor necrosis factor - a secretion, is mostly genetically determined and have been associated with HLA - DR haplotypes and polymorphisms in the tumor necrosis factor - a promoter. Particular interest has been focused on the position - 238 and - 308, both involving the substitution of guanine by adenosine in the uncommon...
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