CD84 is a 64-82 kD glycoprotein. It is a member of the SLAM (CD150) family, a CD2 subset of the Ig superfamily, also known as SLAMF5 or Ly9b. CD84 is expressed on B cells, monocytes, thymocytes, subset of (preferentially on CD45RO+) T cells, and platelets. CD84 functions as a homophilic adhesion molecule and enhances T cell activation and cytokine production. The antibody CD84.1.21 is able to enhance CD3 induced IFN-γ production and partially block CD84-Ig binding to lymphocytes.