An antigen is a substance/molecule that, when introduced into the body, triggers the production of an antibody by the immune system, which will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader.
agglutinin [əˈgluːtɪnɪn]n (Life Sciences & Allied Applications / Biology) a substance, such as an antibody or a lectin, that causes agglutination of cells or bacteria
Antibodies (also known as immunoglobulins, abbreviated Ig) are gamma globulin proteins that are found in blood or other bodily fluids of vertebrates, and are used by the immune system to identify and neutralize foreign objects, such as bacteria and viruses.
The Rh (Rhesus) blood group system (including the Rh factor) is one of the currently 30 human blood group systems. It is clinically the most important blood group system after ABO. The Rh blood group system currently consists of 50 defined blood-group antigens, among which the 5 antigens D, C, c, E, and e are the most important ones. The commonly-used terms Rh factor, Rh positive and Rh negative refer to the D antigen only. Besides its role in blood transfusion, the Rh blood group system, in particular the D antigen, is a relevant cause of the hemolytic disease of the newborn or erythroblastosis fetalis for which prevention is key.
Hemolytic disease of the newborn (HDN)A pregnant woman can make IgG blood group antibodies if her fetus has a blood group antigen that she does not have. This can happen if some of the fetus' blood cells pass into the mother's blood circulation (e.g. a small fetomaternal hemorrhage at the time of childbirth or obstetric intervention), or sometimes after a therapeutic blood transfusion. This can cause Rh disease or other forms of hemolytic disease of the newborn (HDN) in the current pregnancy and/or subsequent pregnancies. If a pregnant woman is known to have anti-D antibodies, the Rh blood type of a fetus can be tested by analysis of fetal DNA in maternal plasma to assess the risk to the fetus of Rh disease. One of the major advances of twentieth century medicine was to prevent this disease by stopping the formation of Anti-D antibodies by D negative mothers with an injectable medication called Rho(D) immune globulin. Antibodies associated with some blood groups can cause severe HDN, others can only cause mild HDN and others are not known to cause HDN.