Blood groups such as A, B, AB and O are identified by cell surface antigens.There are four major blood groups determined by the presence or absence of two antigens – A and B – on the surface of red blood cells: Since some antigens can trigger a patient's immune system to attack the transfused blood, safe blood transfusions depend on careful blood typing and cross-matching. Neutralisation of viruses and bacteria – Antibodies can bind to the surface of viruses, preventing them from entering host cells.īlood types are determined by the presence or absence of certain antigens – substances that can trigger an immune response if they are foreign to the body.Antibodies bound to the surface of a pathogen activate a complement cascade which leads to the formation of a “membrane attack complex” that forms a pore in the membrane of the pathogen allowing water and ions to enter into the cell, causing the cell to lyse. Complement activation – The complement system is a collection of proteins which ultimately lead to the perforation of the membranes of pathogens.Neutralisatio n of toxins – Antibodies bind to toxins produced by pathogens in the blood plasma preventing them from affecting susceptible cells.Opsonisation – Antibodies make pathogens recognizable by binding to them and linking them to phagocytes.The large agglutinated mass can be filtered by the lymphatic system and then phagocytised. These clumped masses of pathogens are then easily ingested and destroyed by phagocytes. Agglutination – Antibodies cause the sticking together of pathogens by attaching to the antigens on the surface.These light chain types are identified as kappa and lambda chains. The light chains found in immunoglobulins exist in two major forms. The differences in subclasses are based on small variations in the heavy chain units of antibodies in the same class. There are also a few subclasses of immunoglobulins in humans. The heavy chain type in IgE is an epsilon chain. IgE: Found mostly in saliva and mucus, these antibodies are involved in allergic responses to antigens.The heavy chain type in IgD is a delta chain. IgD molecules are located on the surface membranes of mature B cells. IgD: The role of these antibodies in the immune response is currently unknown.The heavy chain type in IgA is an alpha chain. IgA: Located mainly in body fluids such as sweat, saliva, and mucus, these antibodies prevent antigens from infecting cells and entering the circulatory system.The heavy chain type in IgM is a mu chain. IgM molecules play a major role in the primary immune response as the initial respondents to new antigens in the body. Each Y-shaped section is attached to a joining unit called a J chain. They contain five Y-shaped sections each with two light chains and two heavy chains. IgM: Of all of the immunoglobulins, these are the most massive.The heavy chain type in IgG is a gamma chain. They can cross blood vessels and even the placenta to provide protection to a fetus. IgG: These molecules are the most plentiful in circulation.Immunoglobulin classes differ in the structure of the heavy chains in each molecule. These classes are identified as IgG, IgM, IgA, IgD, and IgE. Five primary classes of antibodies exist with each class playing a distinct role in the human immune response.
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