Blood group antigens: Molecules seeking a function?

The blood group antigens have been dismissed by some researchers as merely 'icing on the cake' of glycoprotein structures. The fact that there are no lethal mutations and individuals have been described lacking ABO, H and Lewis antigens seems to lend weight to the argument. This paper reviews the research which suggests that these antigens do indeed have function and argues that blood group antigens play important roles in modulation of protein activity, infection and cancer. It explores the evidence and poses questions as to the relevance and implications of the results.