CD80, also known as B7-1, is a protein found on dendritic cells, activated B cells, and monocytes. It provides necessary co-stimulatory signals for T cell activation and survival. The cDNA of CD80 is predicted to encode a type I transmembrane protein, which is synthesized on the endoplasmic reticulum with a signal peptide. The predicted protein contains two extracellular domains with structural similarity to immunoglobulins (Ig), a hydrophobic transmembrane region, and a short cytoplasmic domain. The CD80 gene, along with the CD86 gene, encodes B7-1 and B7-2, respectively, which are structurally related members of the immunoglobulin superfamily expressed on various hematopoietic cell types. B7-1 and B7-2 provide co-stimulatory signals to T cells by interacting with CD28 and CTLA4.