Cytotoxic T lymphocyte antigen 4 (CTLA-4) is a T lymphocyte surface molecule that plays a role in regulating the immune response. This molecule also plays an important role in regulating T cell activation and can limit the T cell response in accordance with inflammatory conditions. CTLA-4 Ig is a soluble chimeric protein and has a negative regulatory function in the body. When a foreign substance tries to enter the body, T cells become active and if this response shows excessive activation, it can damage normal and healthy cells and tissues, so it should be kept under control. It has been reported that genetic diversity in CTLA-4 may play a role in the development of autoimmune diseases. It is recommended that CTLA-4 be investigated in more detail to examine its effects by looking at the levels of CTLA-4 in the course of autoimmune diseases. It is thought that further investigation of CTLA-4 may contribute to immunotherapy and cancer treatments