CD24 (also known as heat stable antigen) is a phosphatidylinositol linked cell surface glycoprotein with a polypeptide core of 30 amino acids and high carbohydrate content. The apparent molecular mass of the two forms of CD24 purified from a mouse lymphoma cell line appear to be in the range of 40-60 and 23-30 kDa. CD24 is expressed at all stages of B cell development and on most thymocytes. The absence of expression from mature T cells is closely associated with their maturation from CD4+ CD8+ CD24+ thymocytes to either CD4+ CD8- CD24- or CD4- CD8+ CD24- T cells. CD24 is also present on mouse granulocytes, monocytes, Langerhans cells and erythrocytes. Its ligand is P selectin (CD62P). CD24 may play a role in regulation of B cell proliferation and differentiation, and it has been proposed that heat stable antigen promotes homotypic adhesion between B lymphocytes. CD24 is also a positive marker of pancreatic cancer.