Identifies cytotoxic/suppressor T-cells that interact with MHC class I bearing targets. CD8 is thought to play a role in the process of T-cell mediated killing. CD8 alpha chains binds to class I MHC molecules alpha-3 domains. In general heterodimer of an alpha and a beta chain linked by two disulfide bonds. Can also form homodimers. Shown to be expressed as heterodimer on thymocytes and as homodimer on peripheral blood T-lymphocytes. Interacts with the MHC class I HLA-A/B2M dimer. Interacts with LCK in a zinc-dependent manner. 2 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.