Blood group - The importance of antigens and antibodies | meer-bezoekers.info
The study of such reactions is known as serology. In this reaction, the epitopes of antigen reacts with paratopes of antibody forming antigen-antibody complex. Soluble antigens combine with antibodies in presence of electrolyte at suitable temperature and pH to form insoluble. The association between an antigen and antibody involves various .. The main difference between these two reactions is the size of antigens.
The combination of pregnancy and transfusion is a particularly potent stimulus. Individual blood group antigens vary in their antigenic potential; for example, some of the antigens belonging to the Rh and ABO systems are strongly immunogenic i. The blood group antigens are not restricted solely to red cells or even to hematopoietic tissues.
The antigens of the ABO system are widely distributed throughout the tissues and have been unequivocally identified on platelets and white cells both lymphocytes and polymorphonuclear leukocytes and in skin, the epithelial lining cells of the gastrointestinal tractthe kidney, the urinary tract, and the lining of the blood vessels.
Evidence for the presence of the antigens of other blood group systems on cells other than red cells is less well substantiated. Among the red cell antigens, only those of the ABO system are regarded as tissue antigens and therefore need to be considered in organ transplantation. Chemistry of the blood group substances The exact chemical structure of some blood groups has been identified, as have the gene products i.
Blood group antigens are present on glycolipid and glycoprotein molecules of the red cell membrane. The carbohydrate chains of the membrane glycolipids are oriented toward the external surface of the red cell membrane and carry antigens of the ABOHh, Ii, and P systems. Glycoproteinswhich traverse the red cell membrane, have a polypeptide backbone to which carbohydrates are attached.
Another integral membrane glycoprotein, glycophorin Acontains large numbers of sialic acid molecules and MN blood group structures; another, glycophorin Bcontains Ss and U antigens. The genes responsible for inheritance of ABH and Lewis antigens are glycosyltransferases a group of enzymes that catalyze the addition of specific sugar residues to the core precursor substance. For example, the H gene codes for the production of a specific glycosyltransferase that adds l-fucose to a core precursor substance, resulting in the H antigen; the Le gene codes for the production of a specific glycosyltransferase that adds l-fucose to the same core precursor substance, but in a different place, forming the Lewis antigen; the A gene adds N-acetyl-d-galactosamine H must be presentforming the A antigen; and the B gene adds d-galactose H must be presentforming the B antigen.
The P system is analogous to the ABH and Lewis blood groups in the sense that the P antigens are built by the addition of sugars to precursor globoside and paragloboside glycolipids, and the genes responsible for these antigens must produce glycosyltransferase enzymes.
The genes that code for MNSs glycoproteins change two amino acids in the sequence of the glycoprotein to account for different antigen specificities. Additional analysis of red cell membrane glycoproteins has shown that in some cases the absence of blood group antigens is associated with an absence of minor membrane glycoproteins that are present normally in antigen-positive persons.
Methods of blood grouping Identification of blood groups The basic technique in identification of the antigens and antibodies of blood groups is the agglutination test. Agglutination of red cells results from antibody cross-linkages established when different specific combining sites of one antibody react with antigen on two different red cells. By mixing red cells antigen and serum antibodyeither the type of antigen or the type of antibody can be determined depending on whether a cell of known antigen composition or a serum with known antibody specificity is used.
In its simplest form, a volume of serum containing antibody is added to a thin suspension 2—5 percent of red cells suspended in physiological saline solution in a small tube with a narrow diameter.
After incubation at the appropriate temperature, the red cells will have settled to the bottom of the tube. IgG antibodies are the most common and the most important. They circulate in the blood and other body fluids, defending against invading bacteria and viruses. The binding of IgG antibodies with bacterial or viral antigens activates other immune cells that engulf and destroy the antigens. The smallest of the antibodies, IgG moves easily across cell membranes.
In humans, this mobility allows the IgG in a pregnant woman to pass through the placenta to her fetus, providing a temporary defense to her unborn child. IgA antibodies are present in tears, saliva, and mucus, as well as in secretions of the respiratory, reproductive, digestive, and urinary tracts. IgA functions to neutralize bacteria and viruses and prevent them from entering the body or reaching the internal organs.
Antibody and antigen
IgM is present in the blood and is the largest of the antibodies, combining five Y-shaped units. It functions similarly to IgG in defending against antigens but cannot cross membranes because of its size.
- Antigen-antibody interaction
IgM is the main antibody produced in an initial attack by a specific bacterial or viral antigen, while IgG is usually produced in later infections caused by the same agent. Words to Know Allergen: A foreign substance that causes an allergic reaction in the body. Cells produced in bone marrow that secrete antibodies. The production of antibodies in response to foreign substances in the body.
The condition of being able to resist the effects of a particular disease.
The process of making a person able to resist the effects of specific foreign antigens. To introduce a foreign antigen into the body in order to stimulate the production of antibodies against it. Identical antibodies produced by cells cloned from a single cell. Large molecules that are essential to the structure and functioning of all living cells. Preparation of a live weakened or killed microorganism of a particular disease administered to stimulate antibody production.
IgD is present in small amounts in the blood. This class of antibodies is found mostly on the surface of B cells—cells that produce and release antibodies. IgD assists B cells in recognizing specific antigens. IgE antibodies are present in tiny amounts in serum the watery part of body fluids and are responsible for allergic reactions.
IgE can bind to the surface of certain cells called mast cells, which contain strong chemicals, including histamine. Histamines are substances released during an allergic reaction. They cause capillaries to dilate, muscles to contract, and gastric juices to be secreted. When an allergen such as pollen binds with its specific IgE antibody, it stimulates the release of histamine from the mast cell.
The irritating histamine causes the symptoms of an allergic reaction, such as runny nose, sneezing, and swollen tissues. Tests that detect the presence of specific antibodies in the blood can be used to diagnose certain diseases. Antibodies are present whenever antigens provoke an immune reaction in the test serum.
The immune response When a foreign substance enters the body for the first time, symptoms of disease may appear while the immune system is making antibodies to fight it. Subsequent attacks by the same antigen stimulate the immune memory to immediately produce large amounts of the antibody originally created. Because of this rapid response, there may be no symptoms of disease, and a person may not even be aware of exposure to the antigen.
Antigen-antibody interaction - Wikipedia
They have developed an immunity to it. This explains how people usually avoid getting certain diseases—such as chicken pox—more than once. Immunization Immunization is the process of making a person immune to a disease by inoculating them against it.