The M1/69 antibody reacts with murine CD24, an ~35 – 45 kDa glycoprotein expressed on lymphocytes, granulocytes, thymocytes, erythrocytes, epithelial cells, neurons, and dendritic cells. CD24 is differentially expressed during T and B cell development, and is not found on the majority of mature peripheral T cells or plasma cells. It is expressed on pro-B, pre-B and mature B cells, but expression is strongly down-regulated after B cell activation. CD24 is involved in regulating B cell apoptosis and in preventing terminal differentiation of B cells into antibody-secreting plasmablasts and plasma cells. It acts as an adhesion or co-stimulatory molecule and is involved in lymphocyte activation, proliferation and differentiation through homophilic interactions or by binding to ligands such as P-selectin (CD62P).