Cytotoxic T lymphocyte-associated protein 4 (CTLA-4), a widely studied non-HLA susceptibility gene in autoimmune disorders, is mainly expressed on the surface of regulatory T cells and conventional T cells and suppresses self-reactive T cells responses via downregulating ligand availability for the costimulatory receptor CD28 to elicit inhibitory signals. The gene discussed is CTLA4; the disease is Autoimmunity.