Both PD-1 and its ligands are widely expressed in different cell types (B cells, CD4+ and T CD8+ cells, natural killer cells, and dendritic cells) that physiologically act by limiting the activation and proliferation of T cells, as well as promoting immunological tolerance to self-antigens, preventing auto-inflammatory reactions and autoimmunity in the healthy host40,.41 The gene discussed is CD4; the disease is Autoimmunity.