The 2D10.4 antibody reacts with human CD80, a 60 kDa glycoprotein that is a member of the Ig superfamily. CD80, also known as B7-1, is a ligand for the T cell receptors CD28 and CTLA-4 (CD152). Along with CD86, CD80 plays a major role in regulating the activation of T cells. CD80 is expressed by activated antigen presenting cells including B cells, macrophages, and dendritic cells. Activated T cells have also been reported to express CD80.