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SubsidizedEternity

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Institute of Health Technology, Dhaka

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immunology antigens immunogens biology

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This document provides a quick overview regarding antigens and immunogens. It explores the factors that affect immunogenicity, including foreignness, molecular weight, chemical composition, route, dosage, and degradability. Also included are several types of antigens based on reaction and origin.

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9/11/24 ANTIGEN Substances recognized as foreign by the body and have the capabi...

9/11/24 ANTIGEN Substances recognized as foreign by the body and have the capability to react with a complementary antibody or cell receptor. It can be capsules, cell walls, toxins, viral capsids, and flagella. They can also be non-microbes such as pollen, red blood cell 4 antigen surface molecules, serum proteins, as well as surface molecules from transplanted tissue. IMMUNOGEN macromolecules that are capable of inducing an immune response or stimulating antibody production. immunogenic substances are always antigenic whereas, antigens are not necessarily immunogenic. "ALl IMMUNOGENS are ANTIGENS but not all ANTIGENS are IMMUNOGENS." 1 2 2 PROPERTIES FACTORS AFFECTING IMMUNOGENICITY 1. IMMUNOGENICITY FOREIGNNESS Induce immune response for antibody production MOLECULAR WEIGHT Inherent ability of a substance to induce an immune CHEMICAL COMPOSITION, AND COMPLEXITY ROUTE, DOSAGE, AND TIMING response resulting in the formation of antibodies or DEGRADABILITY immune lymphocytes for antibody production 2. ANTIGENICITY Property of a substance to react specifically with the antibody 3 4 1 9/11/24 1. FOREIGNNESS B. SYNGENEIC ANTIGEN antigens and immunogens must be recognized by the body as non-self. found in individuals of an inbred strain or between The higher the difference, the greater the immune response. identical twins. It can be found in genetically identical individuals. A. AUTOLOGOUS ANTIGEN also referred to as auto antigens. These antigens are not foreign to the body, they are found within the same individual. Sequestered antigens aka hidden antigen Do not usually come in contact with C. ALLOGENEIC ANTIGEN antibody producing cells since they are inaccessible to antibody forming tissues Homologous antigen also referred to as a homologous antigen or alloantigen. Tissue-specific antigens These antigens are found within the same species but Thyroglobulin different individuals. ⚬ thyroid antigen Basic protein ⚬ brain tissue 5 6 d. XENOGENEIC ANTIGEN Graft Heterologous; found across special boundaries Heterogenetic or heterophile antigens transplantation Antigens found across species boundaries. is the act of transferring cells, tissues, or organs from one site to another, typically between different individuals Same individual AUTOGRAFT transplantation of cells, tissues, or organs between sites within the same individual. Example: skin graft. ISOGRAFT aka Syngraft; identical individuals graft taken from a donor, genetically identical to the recipient. Different individuals but same species ALLOGRAFT Transplantation of organs or tissues from a donor to a non- genetically identical individual of the same species. Most common XENOGRAFT Different species 7 8 2 9/11/24 2. MOLECULAR WEIGHT 3. CHEMICAL COMPOSITION AND COMPLEXITY the higher the molecular weight, the better or the more immunogenic the higher the complexity, the more complex the molecules below 5,000 Daltons are non-immunogenic organism is, the greater the immune response The number of epitopes increases proportionately with the size of the antigen that it can induce or initiate PROTEIN EPITOPE majority of immunogens are proteins strongest immunogens among the an epitope is the determinant site on an antigen different biochemical unit of life considered as the most immunogenic GLYCOPROTEINS CATEGORY MOL. WT. EXAMPLE RBC blood group antigen A, B and Rh POTENTIAL IMMUNOGEN > 10,000 Daltons Serum albumin antigens GOOD IMMUNOGEN > 40,000 Daltons Gamma globulin comprised of protein and carbohydrate chains EXCELLENT IMMUNOGEN > 1,000,000 Daltons Hemocyanin 9 10 POLYSACCHARIDES most are incomplete immunogens because they do 3. route, dosage and timing not possess sufficient chemical diversity Generally, intravenous and intraperitoneal routes are effective 2 Forms: Intradermal routes offer the strongest stimulus than the subcutaneous and ⚬ Pure polysaccharide substances ⚬ Lipopolysaccharides intramuscular route The smaller the dose, the less likely the immune response ■ constituent of the outer membrane of the gram-negative bacteria ■ aka endotoxin 4. DEGRADABILITY The immunogen needs to be degraded and presented to the cells of the immune NUCLEIC ACIDS system ⚬ T-dependent antigens – include proteins non-immunogenic because of relative simplicity & ⚬ T-independent antigens – carbohydrates and other polysaccharides rapid degradation LIPIDS non-immunogenic; few can act as haptens relatively simple and lack structural ability 11 12 3 9/11/24 HAPTEN PHYSICAL NATURE OF ANTIGEN Low molecular weight compound which by itself Foreignness degree to which antigenic determinants are recognize as non-self by an individual’s cannot elicit the formation of antibodies immune system Incomplete/partial antigen Has the chemical configuration which gives the Degradability For an antigen to be recognized as foreign by an individual’s immune system, antigen its antibody-provoking ability sufficient antigens to stimulate immune response must be present. BASIC CHARACTERISTICS OF ANTIGENS Molecular weight The higher the molecular weight, the better the molecule will function as an antigen It must be foreign structural stability is mandatory because if a structure is unstable, we say that the It must have a high molecular weight Structural stability molecule will be poor antigen. It must gain entrance into the body It is usually a protein or a complex Complexity the more complex the antigen the greater is its effectiveness polysaccharide in nature It must possess a high order of specificity 13 14 parts of an antigen PARTS OF THE ANTIGEN a. carrier CARRIER DETERMINANT GROUP represents the greater bulk of the antigen. It is almost always protein in nature and has the ability to Reactive portion of an antigen which compresses induce an immune response. Great bulk of antigen about five to seven amino acids residue or its equivalent monosaccharide residue B. epitope High molecular weight Low molecular weight Small part of an antigen that interacts with an antibody Almost always protein in nature Variable in nature; carbohydrate, lipid or amino acids Any given antigen may have several epitopes Each epitope is recognized by a different antibody Cannot invoke antibody production but can react with Can cause production of antibody its homologous antibody 15 16 4 9/11/24 classification of antigen B. Based on Reaction a. Based on Structure and Function AGGLUTINOGEN acted upon by a specific agglutinin or antibodies; agglutination PRECIPITINOGEN acted upon soluble precipitins; precipitation COMPLETE: ⚬ all attributes of immunogenicity VIRUS acted upon by neutralizing antibodies TOXIN poisonous substance elaborated by certain organisms. HAPTEN: They are neutralized by antitoxins in antitoxin neutralization reactions. ⚬ SIMPLE: ALLERGEN induce allergy. Acted upon by antibodies in allergic reaction ■ It has a single determinant or combining site ■ It is considered monovalent ANAPHYLACTOGEN allergens that participate in anaphylactic reactions. Capable of stimulating antibody formation ■ The reaction is not visible in-vitro ⚬ COMPLEX: ■ they have 2 or more combining sites ■ considered as multivalent/polyvalent ■ reactions of complex reactions are visible in vitro 17 18 Isosensitization C. Based on Origin or Source refers to the antibody production by an AUTOLOGOUS antigen found in the same individual individual following introduction of an SYNGENEIC found between genetically identical individuals antigen from another member of the same species ALLOGENIC also known as homologous antigen. Different individuals, same species XENOGENEIC heterologous antigens. different individuals, different species Heterosensitization antigens that are not exposed to antibody producing cells and become immunogenic refers to the production of antibodies SEQUESTERED when exposed to antibody forming tissues when antigens from one species is aka hidden antigens introduced to another HETEROGENETIC occur in unrelated animal/plant species /HETEROPHILIC capable of cross-reaction due to their identical or closely related structures autosensitization this is the production of antibodies by an individual against an antigen that he himself possesses. self-antigens 19 20 5 9/11/24 superantigens IMMUNOLOGIC ADJUVANT CLASS OF ANTIGENS THAT CAUSE NONSPECIFIC ADJUVANTS ARE SUBSTANCES THAT ENHANCE T-CELL ACTIVATION AND EXPRESSION OF COSTIMULATORS ACTIVATION OF T-CELLS, RESULTING IN POLYCLONAL AN ADJUVANT IS NOT IMMUNOGENIC, AND IT CANNOT INDUCE AN ANTIBODY RESPONSE ON ITS OWN. T-CELLS ACTIVATION AND MASSIVE CYTOKINE THESE ARE SUBSTANCES THAT ARE ADDED TO VACCINES AND LESS IMMUNOGENIC SUBSTANCES TO RELEASE. ENHANCE IMMUNE RESPONSE. SUPERANTIGENS ARE PRODUCED BY SOME PATHOGENIC VIRUSES AND BACTERIA MOST LIKELY AS A DEFENSE MECHANISM AGAINST THE IMMUNE SYSTEM examples: Staphylococcal enterotoxins Staphylococcal toxic shock toxin Staphylococcal exfoliating toxins Streptococcal pyrogenic exotoxins 21 22 How do these adjuvants enhance immune responses? Types of adjuvants Complete Freund’s adjuvant Alum adjuvant THEY INCREASE THE NUMBER OF CELLS INVOLVED IN THE IMMUNE RESPONSE.. contain light mineral oil, an emulsifying aluminum hydroxide with absorbed antigen THEY PROVIDE MORE EFFICIENT ANTIGEN PROCESSING agent, and 0.5mg/mL of killed mycobacteria (Mycobacterium butyricum or Mycobacterium tuberculosis) Synthetic Muramyl Peptide THEY PROLONG THE PRESENCE OF THE IMMUNOGEN OR ANTIGEN will induce granuloma formation at the site stimulates both B-cells and T-cells of injection which slows immunogen THEY INCREASE THE RATE OF SYNTHESIS AND RELEASE OF release ANTIBODIES Incomplete Freund’s adjuvant light mineral oil and an emulsifying agent only Lipopolysaccharide and Endotoxin enhance humoral immunity by stimulating B-cells. They enhance the release if IgM and they induce high fever 23 24 6

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