Antibody Terminology

There are many ways that antibodies can be classified:

• Alloantibodies (once called isoantibodies or isohemagylutinins) are antibodies directed against antigens found in an individuals of the same species.

• Xenoagglutinins (heteroagglutinins) are antibodies directed against antigens found in another species (foreign species), e.g., antiglobulin serum made by rabbits directed against human IgG.

• Autoantibodies are antibodies that react with the red cells of the individuals in whose sera they are found.

• Blocking antibodies refer to incomplete (IgG) antibodies that coat and block red cell antigenic sites so that cells cannot be agglutinated by antisera of the same specificity as the coating antibodies. For example, an Rh(D)-positive newborn may type an Rh(D)-negative if maternal anti-D has coated and blocked all of the D antigens on the infant's red cells.

• Hemolysins are antibodies that can bind complement to C9 and cause red cells to lyse. Few antibodies can do this; examples include antibodies in the ABO system and (rarely) antibodies in the Lewis and Kidd systems. Some additional common antibody terms are given in Table 2-3.

Antibody Terminology