**7. Action of methotrexate on activated KC-immunocyte cycle in psoriasis**

The epidermis is a multilayered epithelium consisting mainly of proliferating and differentiated, postmitotic KCs [145]. The latter derive from transit amplifying cells originating from stem cells that represent a restricted number of basal KCs [146, 147]. The proliferation and differentiation of epidermal KCs is regulated by a multitude of signaling cascades and transcription factors including Wnt/b-catenin [148], growth factors of the EGF and FGF family [149], TGF-β, members of the NFkB family [150], and c-Myc [151].