CD229 is a 100-120 kD glycoprotein. It is a member of the SLAM family, a CD2 subset of the Ig superfamily, known as Ly9 or SLAMF3. CD229 is expressed on T cells, B cells, NK cells, and thymocytes. It functions as a homophilic adhesion molecule through binding to CD229 itself. The cytoplasmic tail of CD229 binds to SAP and Grb2 proteins. CD229 is involved in enhancing T cell activation and Th2 polarization.