ABO blood groups in humans
With these antigens A and B, there are certain naturally occurring antibodies in the serum of the blood. General principle of antibody and antigen relationships is, that antibodies in a particular individual will be found only for those antigens which are absent in blood of this individual. The status of antigens and antibodies in different blood groups is shown in Table 5.7.
Table 5.8 suggests that, if donor's blood has antibodies against that of recipient, it does not matter, since they get diluted. However, there should be no antibodies in recipient's blood against donor's blood, since this will cause agglutinization of transfused blood. It would also be obvious, that AB is universal recipient and no test of donor's blood in such case is necessary. Similarly, O group is universal donor and no test for the recipient's blood is necessary, if blood of O group is available for transfusion.
Fig. 5.3. Effects of anti-A (containing antibody A) and anti-B (containing antibody B) sera on corpuscles of four blood groups (O, A, B and AB). A clumped pattern within a circle shows agglutinization of red blood corpuscles.
The genetics of these blood groups indicates that three alleles are present (i) 1° or i or + (ii) IA or A and (iii) IB or B. lA and IB are mutant alleles and are dominant over the wild allele 1° or i or +. This is based on the concept that wild type is one which is more frequent. O and AB blood groups are more frequent and if O is assumed as wild, it yields a convenient system. The genotypes of different blood groups are shown in Table 5.9.
Fig. 5.3. Effects of anti-A (containing antibody A) and anti-B (containing antibody B) sera on corpuscles of four blood groups (O, A, B and AB). A clumped pattern within a circle shows agglutinization of red blood corpuscles.
Besides series of ABO blood groups, there are other series like MN blood groups. In case of MN series, human blood serum does not contain any specific antibodies, which will cause agglutinization of any blood group in this series. But if the human blood is injected in rabbit, it causes production of specific antibodies responsible for agglutinization of blood type injected. For instance, if blood of M group is injected in rabbit, it will cause production of antibodies in serum (anti-M serum) causing agglutinization of M as well as MN but not of N. Reverse will be the case, when blood of N type is injected in rabbit, so that anti-N serum produced in rabbit causes agglutinization of N and MN, but not of M.
Blood groups sometimes help to decide cases of disputed parentage in criminal courts, because a particular pair of blood groups in parents may give some and not all blood groups in progeny. Therefore, if a child has a blood group, which is not likely to result from the blood groups of a married couple claiming parentage, then it is proved that the child has a doubtful parentage or in other words is illegitimate. Various possible pairs of blood groups of the parents, their children and the impossible blood groups are given in Table 5.12 for ABO blood groups and in Table 5.13 for MN blood groups. In recent years, however, technique of DNA fingerprinting has become available to decide cases of disputed parentage (see Human Genetics).
Rh factor was discovered by Landsteiner and Wiener in 1940 from rabbits immunized with the blood of rhesus monkeys (Macacus rhesus). The resulting antibodies in rabbit serum agglutinated blood of not only rhesus monkeys, but also of certain percentage of human beings and these human beings were called Rh+ (Rh positive). The Rh antigen can produce antibodies in human serum also, which may be possible through wrong transfusion of blood. Therefore, to avoid agglutinization, cross-compatibility of Rh factor as well as ABO blood groups is necessary before transfusion of blood is made. Rh negative individuals should always be given Rh-negative blood to avoid subsequent reaction due to antibody formation.