The CD80 antigen (B7, BB1) recognizes a 60 kDa transmembrane glycoprotein, member of the immunoglobulin family. This molecule shares with CD86 the capability to be the ligand for two structurally similar molecules expressed on T lymphocytes, CD28 and CD152 (CTLA-4). CD80 antigen is expressed on in vitro activated B lymphocytes. It is not expressed on the majority of resting B cells from peripheral blood but identifies a subpopulation of B cells that has been previously activated. The antigen is also expressed by HTLV-1 transformed T cells activated monocytes, and constitutively on dendritic cells. CD80 binding provides costimulatory signals for T cell activation.
