CD200 (also known as OX2 or MRC) is a type-1 membrane glycoprotein, which contains two extracellular immunoglobulin domains, transmembrane domain and cytoplasmic domain. It is expressed by neuronal cells, B and T cell subsets, follicular dendritic cells, keratinocytes, and ovarian cells. The interaction between CD200 and its receptor CD200R results in macrophage activation (IL-6 production), inhibition of mast cell degranulation along with reduced TNF-alpha and IL-13 secretion and overall attenuation of the activation status of lymphocytes. It seems CD200 is also involved in maternal tolerance and its decreased expression in hair follicle correlates with follicular miniaturization.