Serology: ABO and Rh (D) blood group system Introduction Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells. In vertebrates, it is composed of blood cells suspended in a liquid called blood plasma. Vertebrate blood is bright red when its hemoglobin is oxygenated. Normally, 7-8% of human body weight is from blood. Blood is a highly specialized tissue composed of more than 4,000 different kinds of components. Four of the most important ones are red cells (Erythrocyte), white cells (Leukocyte), platelets (Thrombocytes), and plasma. Blood is circulated around the body through blood vessels by the pumping action of the heart. This essential fluid carries out the critical functions of transporting oxygen and nutrients to our cells and getting rid of carbon dioxide and other waste products. In addition, it plays a vital role in our immune system and in maintaining a relatively constant body temperature. Blood is a highly specialized tissue composed of many different kinds of components produced in bone marrow. All humans produce these blood components--there are no populational or regional differences. Red cells, or erythrocytes, are relatively large microscopic cells without nuclei. These cells normally make up 40-50% of the total blood volume. They transport oxygen from the lungs to all of the living tissues of the body and carry away carbon dioxide.
The red cells remain viable for only about 120 days before they are removed from the blood and their components recycled in the spleen. White cells, or leukocytes, exist in variable numbers and types but make up a very small part of blood's volume--normally only about 1%. Most are produced in our bone marrow from the same kind of stem cells that produce red cells. Some white cells (called lymphocytes) are a major part of the immune system. Individual white cells usually only last 18-36 hours before they are also removed from the system. Platelets or thrombocytes are cell fragments without nuclei that work with blood clotting chemicals at the site of wounds. They do this by adhering to the walls of blood vessels, thereby plugging the rupture in the vascular wall. They also can release coagulating chemicals which cause clots to form in the blood that can plug up narrowed blood vessels. Plasma is the relatively clear liquid protein and salt solution, which carries the red cells, white cells, and platelets. Normally, 55% of our blood's volume is made up of plasma. About 95% of it consists of water. As the heart pumps blood to cells throughout the body, the plasma brings them nourishment and removes the waste products of metabolism. Plasma also contains blood clotting factors, sugars, lipids, vitamins, minerals, hormones, enzymes, antibodies, and other proteins. Sometimes when the blood of two people is mixed together, it clumps or forms visible islands in the liquid plasma--the red cells become attached to one another and this is known as agglutination. When different types of blood are mixed within the body, the reaction can be a bursting of the red cells as well as agglutination. The compositional difference between blood types is in the specific kinds of antigens found on the surface of the red cells. Antigens are relatively large protein molecules that
provide the biological signature of an individual's blood type. Within blood there are substances called antibodies which distinguish particular antigens from others, causing bursting or agglutination of the red cells when alien antigens are found. The antibodies bind to the antigens. In the case of agglutination, the antibodies glue together the antigens from different red cells thereby sticking the red cells together. ABO blood group system On the basis of this agglutination factors many blood groups have been identified. One such blood group system, having medical importance is ABO blood group system discovered in 1900 and 1901 at the University of Vienna by Karl Landsteiner, comprising A, B and O type. Decastello and Sturli (1902) discovered the fourth group, AB of the system. Subsequent discovery of of subdivision of A as A 1 and A 2 (Dubgren and Hirzfeld 1911) and A 3 (Freidenreich, 1936) have been discovered. All humans can be typed for the ABO blood group. There are four principal types: A, B, AB, and O. There are two antigens and two antibodies that are mostly responsible for the ABO types. The specific combination of these four components determines an individual's type in most cases. For ABO blood group the nomenclature had been designated as the presence of either A antigen or B antigen as A blood group and B blood group respectively. On the other hand, both the antigens are present termed as AB blood group, while absences of both antigens are known as O blood group. Therefore, for ABO blood group system there are two antigens are A and B, along with two antibodies Anti A and Anti B.
ABO Blood Type Antigen Antigen A B Antibody Antibody anti-a Anti-B A yes no no yes B no yes yes no O no no yes yes AB yes yes no no ABO blood types are inherited through genes on chromosome 9, and they do not change as a result of environmental influences during life. The mode of inheritance An individual's ABO type is determined by the inheritance of 1 of 3 alleles (A, B, or O) from each parent. The possible outcomes are Parent Alleles A B O A AA (A) AB (AB) AO (A) B AB (AB) BB (B) BO (B) O AO (A) BO (B) OO (O) The mode of inheritance of ABO blood group (Bernstein, 1924) demonstrated both A and B alleles are dominant over O. As a result, individuals who have an AO genotype will have an A phenotype. People who are type O have OO genotypes. In other words, they inherited a recessive O allele from both parents. The A and B alleles are co-dominant. Therefore, if an A is inherited from one parent and a B from the other,
the phenotype will be AB. Agglutination tests will show that these individuals have the characteristics of both type A and type B blood. Interesting observation on Bombay Phenotype (Oh) observed (Bhende et al., 1952) have provided valuable insight into genetical pathways involved in the synthesis of the of the ABO blood group antigens. Several associations between ABO blood groups and various diseases have been reported in literature. Worldwide distribution of ABO blood group (Mourant et al., 1976) revealed cliner distribution in terms of high frequency of A blood group in the Western part of the world and progressive increase of B blood group in Eastern sector of the world and O blood group being features in North America. In Indian context average value of B blood group is higher than A blood group but overall frequency of O is highest. Rh Blood Types Rh blood types were discovered in 1940 by Karl Landsteiner and Alexander Wiener. This was 40 years after Landsteiner had discovered the ABO blood groups. Over the last half century, we have learned far more about the processes responsible for Rh types. This blood group may be the most complex genetically of all blood type systems since it involves 45 different antigens on the surface of red cells that are controlled by 2 closely linked genes on chromosome 1. The Rh system was named after rhesus monkeys, since they were initially used in the research to make the antiserum for typing blood samples. If the antiserum agglutinates with individual s red cells, then that individual is Rh+. If it does not, then Rh-. Despite its actual genetic complexity, the inheritance of this trait usually can be predicted by a simple conceptual model in which there are two alleles, D and d. Individuals who are homozygous dominant (DD) or heterozygous (Dd) are Rh+. Those who are homozygous recessive (dd) are Rh- (i.e., they do not have the key Rh antigens). The role of this blood group system in Hemolytic Disease of the New Born
(HDN) (erythroblastosis fetalis) is one of the greatest advancements (Levine et al., 1941) in medical genetics in human serology. Over the last half century, we have learned far more about the processes responsible for Rh types. Subsequent development of Rhesus blood group demonstrated apart from D antigen, there are two closely linked i.e. C and E antigens and becomes as CDE system which present combinations of haplotypes (haploid genotype) on chromosome 1. Inheritance pattern revealed that C, D and E antigens are dominant over c, d and e antigens respectively. Therefore, anthropological interest of this blood group system widens the scope of effective polymorphism study towards selection and maintenance of polymorphism. Distribution of Rhd alleles (RhD negative) ranges rather high frequency in Europe, while towards Asian population it is found to be very nominal. In Indian context RhD alleles (Rh positive) seems to be in very high frequency (almost over 80%), while Rhd alleles (RhD negative) is found to be less than 30% in South, West and North India. On the other hand, East India represent about less than 15% of Rhd alleles (RhD negative). CONCLUSION Blood is an important connective tissue. Apart from its universal nature regarding the components, antigenic determination is related with inheritance pattern and thereby very useful polymorphic trait for population classification.