Psoriasis is a chronic autoimmune disorder that affects 3-4% of the world population. Keratinocytes and immune cells in patient's skin secrets excess pro-inflammatory cytokines that in turn activates the differentiation of T helper cells (Th) into Th1 and Th17 and deactivates Th2 pathway. Several phototherapies have been used in treatment of moderate and severe psoriatic patients; among them narrowband ultraviolet B (NB-UVB, 311 nm) is the most effective. We aims to evaluate the therapeutic effect of NB-UVB exposure in 80 Egyptian plaque psoriatic patients with and without psoriasis arthritis development. This will be accomplished by measuring serum cytokines levels (IL-10, -12, -17, -23 and -34) and high sensitive C reactive protein before and after treatment. A significant elevation in Th2 pathway cytokine, IL-10, and significant decrease in Th1/Th17 pathway cytokines were observed after treatment. This indicates the success of NB-UVB therapy in down modulating IL-12 and IL-23/Th17 axis. The pathological conditions in psoriatic arthritis patients were improved by NB-UVB targeted to the skin. As serum cytokines levels in these patients indicated that the reduction in Th1/Th17 inflammatory cytokines and elevation of Th2 anti-inflammatory cytokines was not restricted to skin lesions only, but also, spread in patients' body and improve their pathologic
