CD86 protein, also known as B7.2, is a crucial cell surface membrane protein belonging to the immunoglobulin superfamily with a molecular weight of approximately 80Kd. It is highly expressed on the surface of antigen-presenting cells. CD86 is expressed in various immune cells, including dendritic cells, monocytes, memory T lymphocytes, germinal center B lymphocytes, activated B lymphocytes, and activated T lymphocytes. CD86 protein plays a pivotal role in the immune system by interacting with CD28 and CTLA-4 (also known as CD152) proteins on the surface of T cells. The binding of CD86 to CD28 serves as a co-stimulatory signal for T cell activation, while the interaction between CD86 and CTLA-4 negatively regulates T cell activation and reduces immune responses. Additionally, CD86 protein contains two extracellular immunoglobulin domains (IgV and IgC), which bind to intercellular adhesion molecule 1 (ICAM-1) and participate in immune cell contact and signal transduction. Abnormal expression of CD86 is closely associated with the occurrence and development of various immune-related diseases. Therefore, understanding the structure and function of CD86 protein is crucial for revealing its immune regulatory mechanisms and providing new theoretical bases for disease treatment. Furthermore, experimental studies have demonstrated that CD86 protein plays a significant role in the activation and differentiation of immune cells, holding potential therapeutic value in immune-related diseases and offering a new breakthrough in the study of immune regulatory mechanisms.