Signal transducer CD24 also known as cluster of differentiation 24 or heat stable antigen CD24 (HSA) is a protein that in humans is encoded by the CD24 gene. CD24 is a cell adhesion molecule. CD24 is a sialoglycoprotein expressed at the surface of most B lymphocytes and differentiating neuroblasts. It is also expressed on neutrophils and neutrophil precursors from the myelocyte stage onwards. The encoded protein is anchored via a glycosyl phosphatidylinositol (GPI) link to the cell surface. The protein also contributes to a wide range of downstream signaling networks and is crucial for neural development. Cross-linking of CD24 on the surface of neutrophils induces apoptosis, and this appears to be defective in sepsis.