الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
The re-discovery of the now termed ”regulatory” T cells re-introduced a pattern of self-tolerance where autoreactivity is regulated by particular subsets of leukocytes. Since then, an explosion of research efforts has uncovered numerous subsets of these cells. Different subsets of Treg cells were defined including natural (nTreg) also known as (constitutive) and inducible (iTreg) also known as (adaptive) populations of Treg cells. The transfer of CD4+CD25− T-cells into athymic nude mice induces various organ-specific autoimmune diseases, whereas, the co-transfer of a small number of CD4+ CD25+ Treg cells could completely prevent the onset of autoimmune diseases. Mice depleted of Treg cells developed multiorgan autoimmune disease, some developed antibodies to dsDNA, glomerulonephritis which are characteristic in SLE. In a human study Treg cells suppression defect was noted in human SLE. In the skin, the number of CD4+CD25+Foxp3+Treg cells in CLE was significantly reduced. In psoriasis, psoriatic Treg cells showed decreased proliferative ability. In bullous pemphigoid, suppression by CD4+CD25+ Treg cells is one mechanism involved in control of self-antigen reactive T-cells and the maintenance of peripheral tolerance in vivo. In pemphigus vulgaris, lower number of Treg cells with reduced suppressor function were present compared with healthy individuals. In alopecia areata, it was found that the skin of mice with chronic alopecia areata and of mice transplanted with alopecia areata affected skin, showed an increased number of CD4+ and CD8+ T-cells, but a strongly low level of CD4+CD25+Treg cells was discovered. In human, studies suggested that there is imbalance between Th1 and Th2 mediated immune responses underlies aberrant Th2 reactions to harmless inhaled allergens. In healthy volunteers, the majority of allergen specific T- cells are of IL-10-secreting Tr1-iTreg subset; while these cells are skewed towards IL-4-secreting Th2 cells in allergic individuals. The balance between allergen-specific Tr1-iTreg cells and Th2 cells is crucial, and any shift in this balance may lead to the development of allergic diseases. In atopic dermatitis, there is mounting evidence of the role of CD4+ CD25+Treg cells in suppressing T-cell responses to allergens. Treg cells have an important role in the suppression of pathogen induced inflammatory responses. Evidence suggests that the activation of Treg cells including both nTreg and Tr1-iTreg cells might result in decreased pathological responses and prolonged persistence of infection as a mechanism for the maintenance of pathogen specific immunologic memory. Regulatory T-cells detected in most of human tumors are of the CD4+CD25+Treg cells population and possess potent ability to suppress immune responses in vitro function. Studies reported that the high percentage of Treg cells in ovarian cancer is associated with the poor prognosis of cancer patients. In naevi, CD4+CD25+Foxp3+Treg cells are present in all groups of lesions. Junctional atypical naevi, compound atypical naevi and melanomas showed the highest percentages of CD4+CD25+Foxp3+Treg cells. The strong prevalence of CD4+CD25+Foxp3+Treg cells in these diseases suggests that they induce immunotolerance during melanoma genesis, favouring melanoma growth. Their evaluation within a tumour site could be useful for prognostic and therapeutic purposes. In cutaneous T-cell lymphomas, there is increased expression of CD4+CD25+Foxp3+Treg cells which known to suppress in vivo immune responses. In conclusion, regulatory T-cells play crucial role in the pathogenesis of wide spectrum of skin diseases through their complex integration in infectious, allergic, immunological and tumoral pathways. Extensive research is strongly recommended to explain the exact roles of these cells in the pathogenesis of these diseases. The possibility of developing new therapies utilizing the knowledge acquired from these researches is promising and represents a major future direction in the management of many complex diseases.