Up regulation of CD200 with concomitant down regulation of its receptor (CD200R)—in peripheral blood or tissues- has been found in systemic lupus erythematosus (SLE) [14], inflammatory bowel disease [15] and rheumatoid arthritis[16], all of which–similar to psoriasis- are characterized by Th17/Treg cell imbalance [17]. Here, CD200 is linked to psoriasis.