UNIT I

Historical introduction to Transfusion medicine (blood banking). Definition and Classification of antigen and antibody.

Classification of antigens and antibodies.

1.1 Historical introduction to Transfusion medicine (blood banking)

Blood transfusion has been in practice since ancient times. Scientific understanding and safe practice of blood transfusion and blood banking were developed over centuries. The following are the brief overviews of the key milestones

• 1. 17th century: Indian, Egyptian, and Greek civilizations are ancient civilizations using blood transfusion practices. They have strong feelings about the power of blood to heal. They used animal blood and human blood in the rituals.

• 2. The first recorded human blood transfusion was attempted by Dr Andreas Libavius in the 15th century. He transfused the blood of one person to another person using animal bladders as containers. This caused an adverse reaction and was unsuccessful. It was mainly due to no knowledge of blood groups, blood clotting mechanisms, and prevention of blood clotting.

• 3. Discovery of blood groups and blood coagulation: In 1628, William Harvey discovered blood circulation. In 1901, Karl Landsteiner identified the ABO blood group. This was the main breakthrough in blood transfusion. It explains mismatch transfusion to cause blood reaction. Karl Landsteiner's work opened the safe blood transfusion. It explained matching of blood groups of blood donors and blood recipients is a must to avoid blood reaction.

• 4. World War and blood transfusion services: Demand for blood transfusion increased during World War I and II. This leads to the establishment of the first blood transfusion service. This blood transfusion service focused on blood collection, blood storage, and blood distribution for blood transfusion to treat soldiers. This leads to the development of blood storage techniques, anticoagulants, and refrigeration to improve the availability of blood for blood transfusion.

• 5. Creation of blood bank: In 1937, Dr Barnard Fantus established the first hospital blood bank in Cook County Hospital, Chicago USA. The main aim of the blood bank was to collect blood and store blood for regular use. This reduced the need for immediate donors in emergency cases. Blood banks became feasible with an increased understanding of blood group compatibility, blood preservation, and refrigeration.

• 6. Advancement in blood screening and Component therapy:

  • The Discovery of the Rh blood group further increases knowledge of blood compatibility.

  • The development of cross-matching techniques helped to ensure compatibility between blood donors and blood recipients. This minimized the risk of complications.

  • Techniques developed to separate blood components like RBCs, WBCs, platelets, plasma, and serum. This developed more targeted blood transfusion. This further reduced the complications after blood transfusion.

• 7. Modern transfusion medicines:

  • Advancements in blood typing, compatibility testing, and improved safety measures led to a new field of medicine modern transfusion medicines.

  • The establishment of standardized protocols advanced screening techniques for infection and enhanced quality control further made blood transfusion safe.

  • In recent years, the development of artificial blood substitutes and techniques has reduced the need of blood donors. But it is an experimental stage.

1.2 Definition of antigen and antibody

Antigen definition

“Antigen is a foreign substance that stimulates an immune response to produce specific antibodies”. Chemically most antigens are protein but some may be carbohydrates, lipids, or nucleic acids. Antigen is present on the surface of foreign cells, pathogens, or molecules entering the human body.

• · Certain cells derived from the inner side of the human body also act as antigens such as tumour cells or transplanted organs.

• · Antigenicity is the antigen's capacity to produce antibodies.

• · Immunogens are the molecules that stimulate the immune system to produce antibodies. Immunogen and antigen are two different components. Antigen stimulates the immune system to produce antibodies. Antigen combines with antibody. Immunogen stimulates the immune system to produce antibodies. However, immunogens do not combine with antibodies.

• · Antigen and antibodies are specific in nature. This means one antigen combines with the specific antibody.

Antibody definition

• · Antibody is also called immunoglobulins “Antibody is specialized protein produced by the immune system upon stimulation by antigen”. Antibody identifies the antigen and neutralizes the antigen.

• · Each antigen is highly specific to a particular antigen. Antibodies circulate in the blood circulation and other body fluids to search for antigens and neutralize antigens.

• · Antibody combines with antigen to form antigen-antibody complex.

1.3 Classification of antigens and antibodies.

Classification of antigens

There are several criteria to classify antigens. The following are some common criteria to classify antigens.

· Classification of antigens based on origin

• 1. Self-antigen (Auto-antigen): These antigens are derived from the individual’s own body. An individual’s immune system develops antibodies to neutralize self-antigen. This develops disease in the individual’s body called autoimmune disease.

• 2. Foreign antigen (Hetero antigen): Antigens enter the human body from outside the environment. The human body's immune system recognizes it to produce antibodies. There are two types of foreign antigens.

  • Ø Nonmicrobial antigen: Non-microbial molecules such as pollen grains, dust, drugs, and chemicals act as antigens and are called non-microbial antigen

  • Ø Microbial antigen: Pathogens such as bacteria, viruses, fungi, or parasites that act as antigens are called microbial antigens.

· Classification of antigens based on structure

• 1. Protein antigens: Surface protein on bacterial cells, viral particles, and protein produced by cancer cells that act as antigens are called protein antigens.

• 2. Polysaccharides antigen: Polysaccharides present on the surface of capsulated bacteria act as antigens and are called polysaccharide antigens.

• 3. Lipid antigens: Lipids associated with certain bacterial cells or fungi cells that act as antigens are called lipid antigens.

• 4. Nucleic acid antigens: Viruses RNA and DNA act as antigens are called nucleic acid antigens.

· Classification of antigens on the basis of immunogenicity

• 1. Immunogens: Large and complex molecules that stimulate the immune system to produce antibodies are called immunogens.

• 2. Haptenes: Small molecules not immunogenic but become immunogenic after combining with larger career molecules are called haptenes.

· Classification of antigens on the basis of blood group

• 1. ABO Antigens: These antigens determine the ABO blood group. They are antigen A and antigen B. They are present on red blood cells' surface.

• 2. Rh Antigen: The Rh system blood group consists of several antigens. Rh antigen present on red blood cell surface is called the Rh+ (positive) blood group and Rh antigen absent on red blood cells is called Rh – (negative blood group). Both ABO antigen and Rh antigen are also called inherited antigens.

· Classification of antigens based on tissues

• Histocompatibility antigen: These antigens are also called human leukocyte antigens (HLAs). They are recognized by the immune system as self-antigen and non-self antigens during organ transplants.

Classification of Antibody (Immunoglobulins)

Antibodies (Immunoglobulins) are classified based on their structure and function. There are five classes of antibodies. These are IgM, IgG, IgA, IgD and IgE.

• 1. IgM: IgM antibody consists of five subunits. It is the first antibody produced by the body in response to infection. It is highly effective to agglutinate with antigens. It helps the body to eliminate pathogens.

• 2. IgG: IgG antibody is the most abundant antibody in blood circulation It is produced by the body in response to primary and secondary infection. It can cross the placental barrier to enter the fetus. It develops passive immunity in the fetus. It has a long half-life. It protects the human body for a longer duration from infection.

• 3. IgA: IgA antibody is found in the breast milk, tears, and mucosal lining of the respiratory tract and digestive system. It is resistant to degradation in the digestive system. It prevents pathogen entry through these surfaces.

• 4. IgD: IgD antibody is present in low concentrations in the blood. Its exact function is not known. It is believed, that it activates B-cells.

• 5. IgE: IgE antibody is involved in allergic reactions and hypersensitivity reactions. It binds with allergens and stimulates the release of histamine. It also protects the body from parasitic infection.

• Author: Dr Pramila Singh