CD4+ T Cells and S100A7 Epression in Normal and Psoriatic Skin: A Histological and Histochemical Study

Psoriasis is one of the commonest and most researched chronic immune-mediated inflammatory skin disorders that affects approximately 1-3% of the population worldwide and significantly impairs patients' quality of life. The most common form is plaque psoriasis, which makes up about 90% of cases, which primarily manifests as sharply demarcated, erythematous, scaly plaques, which can involve any part of the skin but most commonly the extensor surfaces (such as the elbows and knees) and the scalp. Apart from plaque psoriasis, there are also other clinical forms, such as guttate psoriasis (particularly common in children after strep throat infections), and pustular psoriasis (one of the most severe varieties of psoriasis, in which the spreading of pustules is generalized, with epidermal fulfillment and a severe general condition). This disease is characterized by alternating severity and remission of disease symptoms, which include the formation of skin lesions of varying severity. The psoriasis area and severity index (PASI) is a widely used instrument in psoriasis trials that assesses and grades the severity of psoriatic lesions and the patient's response to treatment. It produces a numeric score ranging from 0 to 72. In general, a score of 5 to 10 is considered moderate disease, and a score over 10 is considered severe. A series of basic and clinical studies have shown that psoriasis is mediated by components of both the innate and adaptive immune systems. The crosstalk between keratinocytes and various immune cells, especially helper T cells, plays a central role in the progression of psoriasis. Psoriasis is caused by chronic interaction between keratinocytes and activated immune cells. Numerous studies have established that hyperproliferation and abnormal differentiation of keratinocytes is a secondary phenomenon induced by immune activation. This "immune" hypothesis, is mainly based on dendritic cell (DC) and T cell pathogenic functions.The abnormal expression of