الفهرس 
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Abstract
Extracorporeal photopheresis (ECP) is defined as an immuno-modulatory technique that involves removal of peripheral blood, separation of the buffy coat, and photoactivation with a photosensitizer (8-MOP) and ultraviolet A irradiation before re-infusion of cells. It was developed more than 20 years ago by Edleson to treat erythrodermic T cell lymphoma (CTCL). Most of studies revealed that the mechanism of action of ECP is to induce leucocyte apoptosis, followed by their engulfment by macrophages or other antigen presenting cells, such as immature dendiritic cells in an anti inflammatory cytokin environment. The anti inflammatory cytokine secretion pattern, with a switch from TH1to TH2 for CD4+ lymphocytes, and the engulfment by immature cells without co-stimulatory molecules induces anergy, by deleting effector T- cells that responded to the presented antigens. An increase in regulatory T- cells is also induced after ECP and may contribute to allograft acceptance by the recipient.
However other studies suggest that mechanism of ECP also involves the recruitment and involvement of additional immune cells. Till now it is clear ECP, both activates tumor immunity against cutaneous T cell lymphoma and induce tolerance in auto reactive disorders so understanding the mechanism of action further would help to identify best indications and treatment regimens and optimize the ECP technique.
ECP has shown promising efficacy in a number of sever and difficult to treat conditions, including systemic sclerosis, graft versus host disease, prevention and treatment of rejection in solid organ transplantation and Crohn’s disease. Also the use of ECP in some of these conditions may allow a significant reduction in the use of systemic steroids and other immunosuppressants, reducing long term morbidity and mortality. It has been proved that it is a relatively safe procedure and side effects are relatively safe and transient, sever reactions like vasovagal syncope and infection are uncommon, its disadvantages include practical effort required and high treatment cost.
ECP technique is available in 150 medical centers world wide including USA, Europe, South America and South west Asia. There are three techniques used in extracorporeal photopheresis:
1- UVAR technique first generation 2- UVAR technique second generation 3- Offline technique (UV-MATIC irradiator) A new generation of photopheresis system (CELLEXTM-
Therakos) has recently been launched that promises to simplify therapy in patients with low body weight employing a closed system.