CD77 (globotriaosylceramide Gb3), also known as the Pk blood group antigen, BLA (Burkitt´s lymphoma associated antigen), or CTH (ceramide trihexoside) is a neutral glycosphingolipid composed of three carbohydrate molecules linked to a lipid moiety in the cell membrane (Gal-alpha1-4Gal-beta1-4Glc-beta1-Cer). It is expressed on germinal center B cells, Burkitt´s lymphoma cells, it can be induced on extrafolicular B cells and it is also found on endothelia and epithelia. CD77 may be involved in elimination of germinal center B cells that fail to produce high affinity antibodies, and serves also as receptor for shiga toxin and verotoxin.