Antigen, B7 1

A costimulatory ligand expressed by Antigen-Presenting Cells that binds to CTLA-4 Antigen with high specificity and to CD28 Antigen with low specificity. The interaction of CD80 with CD28 Antigen provides a costimulatory signal to T-Lymphocytes, while its interaction with CTLA-4 Antigen may play a Role in inducing Peripheral Tolerance.