The CD200 and CD200 receptor cell surface proteins interact through their N‐terminal immunoglobulin‐like domains

CD200 (OX2) is a broadly distributed cell surface glycoprotein that interacts with a receptor on myeloid cells (CD200R) involved in regulation of macrophage function. Both CD200 and CD200R contain two Ig superfamily domains like many other leukocyte membrane proteins. Site‐directed mutagenesis of CD200R showed that, like CD200, it interacted through its N‐terminal domain. This indicated that the cell‐cell interaction spans four Ig superfamily domains and this distance is similar to many interactions found between T cells and antigen‐presenting cells. This suggests that this topology is also important in interactions of CD200 on a variety of cells with CD200R on myeloid cells, and comparable contact sites may be important mediating regulation in other cell‐cell interactions. The mutagenesis showed that the binding involved the predicted GFCC′ face of its N‐terminal domain, like that of CD200, suggesting that the interaction evolved from a homotypic interaction.