Leukocyte surface antigen CD53 is a protein that in humans is encoded by the CD53 gene. The protein encoded by this gene is a member of the transmembrance 4 superfamily, also known as the tetraspanin family. The function of this family in a number of different cell types may be involved in transmembrance signal transduction and regulation of cell proliferation and differentiation or both. CD53 is broadly expressed on leukocytes, including B cell, T-cells, monocytes and granulocytes. It has been demonstrated to be a specific and reliable marker for leukocytes. This antibody strongly labels normal and neoplastic cells with hematopoietic origin.