The CD24 antigen is a small heavily glycosylated, glycosylphosphatidylinositol (GPI) linked cell surface protein. It consists of a small protein core comprising 27 amino acids, which is extensively glycosylated and is bound to the membrane via a phosphatidylinositol anchor. The CD24 antigen is physiologically expressed in developing or regenerating tissue, as well as in granulocytes, keratinocytes and renal tubular epithelium. It modulates B-cell activation responses. Signaling could be triggered by the binding of a lectin-like ligand to the CD24 carbohydrates, and transduced by the release of second messengers derived from the GPI-anchor.