CD43, also known as leukosialin or sialophorin, is a type I transmembrane glycoprotein abundantly expressed on the surface of most hematopoietic cells, with the exception of erythrocytes and resting B cells. It has a heavily glycosylated extracellular domain and a cytoplasmic tail. CD43 plays multiple roles in immune responses, including regulation of T-cell activation, proliferation, and cytokine production. It also interacts with ERM proteins (ezrin, radixin, moesin) via a specific sequence in its cytoplasmic tail, which is important for its function in cell adhesion and migration. Additionally, CD43 has been implicated in various biological processes such as leukocyte migration, immune cell signaling, and even tumor progression. Its expression and function can vary depending on the cell type and the specific immune context.