CD80 (also known as B7-1) is a member of the B7 family, primarily composed of two immunoglobulin-like domains. CD80 is mainly expressed on the surface of antigen-presenting cells (such as dendritic cells and macrophages) and is involved in the activation and regulation of T cells. By binding to the CD28 and CTLA-4 receptors on the surface of T cells, CD80 regulates immune responses, affecting cytokine production and T cell proliferation.