Lymphocyte phosphatase-associate Phosphoprotein (LPAP) is a transmembrane phosphoprotein of 32 kD, which is only stable when expressed in the presence of the CD45 glycoprotein. It is expressed on both resting and activated T and B lymphocyte, NK cells and thymocytes. Terminally differentiated plasma cells, granulocytes and monocytes do not express LPAP.