Serum soluble CD200 levels in psoriasis patients was measured by ELISA (Human CD200 PicoKine™ ELISA Kit, Boster Biological Technology, Pleasanton CA, USA, Catalog # EK0993)), and CD200R expression level on both peripheral blood monocytes and lymphocytes were measured by flowcytometry using human CD200 R1 conjugated antibody(Human CD200 R1 Fluorescein-conjugated Antibody, Bio-Techne,Minneapolis, Minnesota, USA, Catalog # FAB3414F)). Cells were analyzed on a FACSCalibur flow cytometer using CellQuest pro software (BD Biosciences, San Diego, CA, USA). Membrane fluorescence intensity was estimated and expressed as mean fluorescence intensity (MFI).