CD43, also known as leukosialin or sialophorin, is a highly glycosylated type I transmembrane protein predominantly expressed on most hematopoietic cells, with the exception of resting B cells and erythrocytes. It belongs to the sialomucin superfamily and is one of the largest cell-surface molecules, extending approximately 45 nm from the cell surface. The protein consists of a heavily glycosylated extracellular region, a transmembrane helix, and a small cytoplasmic region. CD43 plays a significant role in immune function, particularly in T-cell activation and proliferation, and is involved in both cell adhesion and cell activation processes. It is actively excluded from the immunological synapse during T-cell activation, a process that requires interactions with ezrin-radixin-moesin （ERM） proteins. Additionally, CD43 has been shown to regulate T helper type 2 differentiation and can act as a co-stimulatory molecule for T-cell activation.