Biosynthesis of the H, A and B antigens involves a series of enzymes (glycosyl transferases) that transfer monosaccharides. The resulting antigens are oligosaccharide chains, which are attached to lipids and proteins that are anchored in the red blood cell membrane. The function of the H antigen, apart from being an intermediate substrate in the synthesis of ABO blood group antigens, is not known, although it may be involved in cell adhesion. People who lack the H antigen do not suffer from deleterious effects, and being H-deficient is only an issue if they need a blood transfusion, because they would need blood without the H antigen present on red blood cells.