CD1b is a 43kD member of the immunoglobulin superfamily also known as R1. It is a type I membrane glycoprotein with structural similarities to MHC class I and is non-covalently associated with B2-microglobulin. In humans, CD1 family consists of group I proteins (CD1a, CD1b, CD1c), group II (CD1d), and group III (CD1e). CD1b plays a role in non-peptide glycolipid antigen presentation to CD1-restricted T cells. It is expressed on cortical double positive and single positive thymocytes, Langerhans cells, and dendritic cells. In addition to antigen presentation, CD1b has been implicated in thymic T cell development.