Cell surface glycoprotein CD2 receptor 4, also known as Cell surface glycoprotein OX2 receptor 4, CD2 cell surface glycoprotein receptor-like 4, CD2RLa, and CD2R4, is a single-pass type I membrane protein which belongs to theCD2R family. CD2 (OX2) is a cell surface glycoprotein that interacts with a structurally related receptor (CD2R) expressed mainly on myeloid cells and is involved in regulation of macrophage and mast cell function. In mouse there are up to five genes related to CD2R with conflicting data as to whether they bind CD2. CD2R4 contains oneIg-like C2-type (immunoglobulin-like) domain and one Ig-like V-type (immunoglobulin-like) domain. CD2R4 is highly expressed in monocytes, NK cells and a subset of NKT cells. It is weakly expressed in granulocytes and B cells (at protein level). CD2R4 is also expressed in brain, lung, testis, thymus, intestine and uterus. and in bone marrow derived-macrophage and dendritic cells and mast cells. CD2R4 is involved in the recruitment or surface expression of the TYROBP receptor.