CD75 is a 43-85 kD type II transmembrane sialyltransferase protein, also known as beta-galactoside alpha-2,6-sialyltransferase. It is a member of glycosyltransferase family that transfers sialic acid from a donor substrate (CMP-sialic acid) to terminal galactose on glycan chains. CD75 is predominately expressed on germinal center originated B cells and lymphomas. It is also found on mature sIg+ B cells and epithelial cells of lung, breast, kidney, and prostate.