IS WEEK-04.pdf

4 antigen 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 surface molec...

4 antigen 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 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." 2 PROPERTIES 1. IMMUNOGENICITY Induce immune response for antibody production Inherent ability of a substance to induce an immune response resulting in the formation of antibodies or immune lymphocytes for antibody production 2. ANTIGENICITY Property of a substance to react specifically with the antibody FACTORS AFFECTING IMMUNOGENICITY FOREIGNNESS MOLECULAR WEIGHT CHEMICAL COMPOSITION, AND COMPLEXITY ROUTE, DOSAGE, AND TIMING DEGRADABILITY 1. FOREIGNNESS antigens and immunogens must be recognized by the body as non-self. The higher the difference, the greater the immune response. 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 antibody producing cells since they are inaccessible to antibody forming tissues Tissue-specific antigens Thyroglobulin thyroid antigen Basic protein brain tissue B. SYNGENEIC ANTIGEN found in individuals of an inbred strain or between identical twins. It can be found in genetically identical individuals. C. ALLOGENEIC ANTIGEN Homologous antigen also referred to as a homologous antigen or alloantigen. These antigens are found within the same species but different individuals. d. XENOGENEIC ANTIGEN Heterologous; found across special boundaries Heterogenetic or heterophile antigens Antigens found across species boundaries. Graft transplantation 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 2. MOLECULAR WEIGHT the higher the molecular weight, the better or the more immunogenic molecules below 5,000 Daltons are non-immunogenic The number of epitopes increases proportionately with the size of the antigen EPITOPE an epitope is the determinant site on an antigen CATEGORY MOL. WT. EXAMPLE POTENTIAL IMMUNOGEN > 10,000 Daltons Serum albumin GOOD IMMUNOGEN > 40,000 Daltons Gamma globulin EXCELLENT IMMUNOGEN > 1,000,000 Daltons Hemocyanin 3. CHEMICAL COMPOSITION AND COMPLEXITY the higher the complexity, the more complex the organism is, the greater the immune response that it can induce or initiate PROTEIN majority of immunogens are proteins strongest immunogens among the different biochemical unit of life considered as the most immunogenic GLYCOPROTEINS RBC blood group antigen A, B and Rh antigens comprised of protein and carbohydrate chains  POLYSACCHARIDES most are incomplete immunogens because they do not possess sufficient chemical diversity 2 Forms: Pure polysaccharide substances Lipopolysaccharides constituent of the outer membrane of the gram-negative bacteria aka endotoxin NUCLEIC ACIDS non-immunogenic because of relative simplicity & rapid degradation LIPIDS non-immunogenic; few can act as haptens relatively simple and lack structural ability 3. route, dosage and timing Generally, intravenous and intraperitoneal routes are effective Intradermal routes offer the strongest stimulus than the subcutaneous and intramuscular route The smaller the dose, the less likely the immune response 4. DEGRADABILITY The immunogen needs to be degraded and presented to the cells of the immune system T-dependent antigens – include proteins T-independent antigens – carbohydrates and other polysaccharides HAPTEN Low molecular weight compound which by itself cannot elicit the formation of antibodies Incomplete/partial antigen Has the chemical configuration which gives the antigen its antibody-provoking ability BASIC CHARACTERISTICS OF ANTIGENS It must be foreign It must have a high molecular weight It must gain entrance into the body It is usually a protein or a complex polysaccharide in nature It must possess a high order of specificity PHYSICAL NATURE OF ANTIGEN Foreignness degree to which antigenic determinants are recognize as non-self by an individual’s immune system Degradability For an antigen to be recognized as foreign by an individual’s immune system, sufficient antigens to stimulate immune response must be present. Molecular weight The higher the molecular weight, the better the molecule will function as an antigen Structural stability structural stability is mandatory because if a structure is unstable, we say that the molecule will be poor antigen. Complexity the more complex the antigen the greater is its effectiveness parts of an antigen a. carrier represents the greater bulk of the antigen. It is almost always protein in nature and has the ability to induce an immune response. B. epitope Small part of an antigen that interacts with an antibody Any given antigen may have several epitopes Each epitope is recognized by a different antibody PARTS OF THE ANTIGEN CARRIER DETERMINANT GROUP Reactive portion of an antigen which compresses about Great bulk of antigen five to seven amino acids residue or its equivalent monosaccharide residue High molecular weight Low molecular weight Almost always protein in nature Variable in nature; carbohydrate, lipid or amino acids Can cause production of antibody Cannot invoke antibody production but can react with its homologous antibody classification of antigen a. Based on Structure and Function COMPLETE: all attributes of immunogenicity HAPTEN: Simple: It has a single determinant or combining site. It is considered monovalent. the reaction not visible in vitro. Complex: they have 2 or more combining sites considered as multivalent/polyvalent reactions of complex reactions are visible in vitro B. Based on Reaction AGGLUTINOGEN acted upon by a specific agglutinin or antibodies; agglutination PRECIPITINOGEN acted upon soluble precipitins; precipitation VIRUS acted upon by neutralizing antibodies TOXIN poisonous substance elaborated by certain organisms. They are neutralized by antitoxins in antitoxin neutralization reactions. ALLERGEN induce allergy. Acted upon by antibodies in allergic reaction ANAPHYLACTOGEN allergens that participate in anaphylactic reactions. Capable of stimulating antibody formation C. Based on Origin or Source AUTOLOGOUS antigen found in the same individual SYNGENEIC found between genetically identical individuals ALLOGENIC also known as homologous antigen. Different individuals, same species XENOGENEIC heterologous antigens. different individuals, different species antigens that are not exposed to antibody producing cells and become immunogenic when SEQUESTERED exposed to antibody forming tissues aka hidden antigens HETEROGENETIC/ occur in unrelated animal/plant species HETEROPHILIC capable of cross-reaction due to their identical or closely related structures  Isosensitization refers to the antibody production by an individual following introduction of an antigen from another member of the same species Heterosensitization refers to the production of antibodies when antigens from one species is introduced to another autosensitization this is the production of antibodies by an individual against an antigen that he himself possesses. self-antigens superantigens class of antigens that cause nonspecific activation of T- cells, resulting in polyclonal T-cells activation and massive cytokine release. 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 IMMUNOLOGIC ADJUVANT adjuvants are substances that enhance T-cell activation and expression of costimulators An adjuvant is not immunogenic, and it cannot induce an antibody response on its own. These are substances that are added to vaccines and less immunogenic substances to enhance immune response. How do these adjuvants enhance immune responses? They increase the number of cells involved in the immune response.. They provide more efficient antigen processing They prolong the presence of the immunogen or antigen They increase the rate of synthesis and release of antibodies Types of adjuvants Complete Freund’s adjuvant Alum adjuvant contain light mineral oil, an emulsifying agent, aluminum hydroxide with absorbed antigen and 0.5mg/mL of killed mycobacteria (Mycobacterium butyricum or Mycobacterium tuberculosis) Synthetic Muramyl Peptide will induce granuloma formation at the site of stimulates both B-cells and T-cells injection which slows immunogen release 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