T-cell surface glycoprotein CD8 alpha chain (CD8) identifies cytoto, Xenopus/Amphibian,ic/suppressor T-cells that interact with MHC class I bearing targets. CD8 is plays a role in the process of T-cell mediated killing. CD8 alpha chains binds to class I MHC molecules alpha-3 domains. Defects in CD8A are a cause of familial CD8 deficiency (CD8 deficiency). Familial CD8 deficiency is a novel autosomal recessive immunologic defect characterized by absence of CD8+ cells, leading to recurrent bacterial infections.