CD80, also known as T-lymphocyte activation antigen CD80, is a member of cell surface immunoglobulin superfamily. This protein can bind to either human or mouse CD28 and CTLA-4. It is expressed on activated B cells, activated T cells, and macrophages. The B7/CD28/CTLA4 pathway has the ability to both positively and negatively regulate immune responses. Therefore, it is considered a promising therapeutic target for autoimmune diseases and various carcinomas.