The Cluster of differentiation 80 (also CD80 and B7-1) is a B7, type I membrane protein[5] in the immunoglobulin superfamily, with an extracellular immunoglobulin constant-like domain and a variable-like domain required for receptor binding. It is closely related to CD86, another B7 protein (B7-2), and often works in tandem. Both CD80 and CD86 interact with costimulatory receptorsCD28, CTLA-4 (CD152) and the p75 neurotrophin receptor.[6][7]