Antigens.lecture note immunology theoretical pptx

lecture note of immunology

1. The Antigens Ahmed KH Hamza Al Aflwky M C S Medical Microbiology and Immunity

2. Antigens INTRODUCTION -The term antigen orginally refered to a substance that is an antibody genereter . Antigen is a substsnce ( usually protein ) in nature and some times polysaccharide, that generater a specific immune response and induces the formation of a specific antibody or specially sensitized T cells or both . Antigens are recoginized by antigen receptor, (including antibodies and T-cell receptor).

3. Immunogen vs Antigen -IMMUNOGEN. -A stimulate that produces a humoral or cell mediated immune response ( I R ) -ANTIGEN. - Antigen is a molecules that can bind to an antibody , B cell receptor or T cell receptor

4. Immunogen vs Antigen Anything that induces specific immune response Substance that reacts with product of immune system (antibody or TCR) protein epitope

5. Immunogen vs Antigen - An immunogen refers to a molecule that is capable of eliciting an immune response by an immune system, whereas an antigen refers to a molecule that is capable of binding to the product of that immune response. - So, an immunogen is necessarily an antigen, but an antigen may not necessarily be an immunogen.

6. Overview of the immune system

7. Epitopes (Antigenic Determinant Sites)

8. Epitopes..continue

9. Epitopes..continue - Site on antigen recognized by an antibody. - Also known as an antigenic determinant . - Epitope is the region on the antigen which is actually responsible for the antigenic properties of the antigen. - An epitope is approximately five or six amino acids in length -Paratope is the corresponding region on the antibody which will bind with epitopes to neutralize it.

10. Haptens (Incomplete antigen) - Hapten is a molecule that reacts with specific antibody but is not immunogenic by itself, it can be made immunogenic by conjugation to a suitable carrier. Many drugs like penicillins are  HAPTEN . - A hapten is essentially an incomplete antigen. These small molecules can elicit an immune response only when attached to a large carrier such as a protein; the carrier typically does not elicit an immune response by itself

11. Hapten .

12. Adjuvant Adjuvant. An adjuvant is a pharmacological or immunological agent that modifies the effect of other agents. Directly immunizing most antigens will lead to a poor immune response and rapid removal of the antigen from the body. To prevent this, the antigen is first combined with an adjuvant, which is a material that helps stimulate and enhance the immune response against the antigen through the creation of a depot effect. 

13. Adjuvant

14. Types of Antigens ( according to sources) - Exogenous antigen These antigen comes from environment and enters the body or system and begin circulating in the body fluids and trapped by the APCs (Antigen presenting cell )such as macrophage , dendritic cells,etc . - Example of exoantigen: - Microbes: cell wall , capsules , toxins viral capsids -non microbes : pollen , egg white ,

15. Types of Antigens - Autoantigen : is usually a self-protein or protein complex (and sometimes DNA or RNA) that recognized by immune system of patients suffering from autoimmune disease. - Alloantigen (Allogeneic): are found in different members of the same species (the red blood cell antigen A and B are example also kidney transplant from mother to daughter). - Xenogeneic ( Heterogeneic ) antigens : are found in different species (e .g a transplant of monkey kidney to human).

16. Types of Antigens - T Cell dependent antigens : - More common, typically protein structure - A help from T helper cells is necessary for specific humoral immune response generating , the response is not so effective . - The help comes in form of cytokines secreted by the T cell. - T Cell independent antigens : - Antibody production can be induced directly , without help from T cell. - Bacterial lipopolysaccharides LPS

17. Superantigens - A type of antigens that cause non-specific activation of T cells, resulting in of polyclonal T cell activation and massive amount of cytokine release . - Antigenic structures, capable to induce response of T cell by external binding to MHC ( major histocompatibility complex ) molecules (out side of the usual binding site) . - Example : Staphylococcal enterotoxins Staphylococcal toxic shock toxin Staphylococcal exfoliating toxin Streptococcal pyrogenic exotoxins

18. Superantigens Definition Polyclonal T cell response Examples Staphlycoccal enterotoxins Toxic shock toxin T cell TCR T cell TCR APC MHC APC MHC Ag SuperAg Monoclonal/Oligoclonal(normal A g) T cell response Polyclonal T cell response(Superantigen)

19. Factors Affecting antigenicity 1- chemical structure and composition - When antigen is more complex the substance is chemically the more immunogenic it will be . A- Protein - Proteins are usually very good immunogens . These may be pure protein or they may be glycoprotein or lipoprotein . B- polysaccharides - Pure polysaccharides and lipopolysaccharides are good immunogens . C-Nucleic Acids are usually poorly immunogens but may become immunogens when single strand or when complexed with protein. D - Lipids in general lipids are non immunoges , although they may be haptens .

20. Factors Affecting antigenicity Immunogenicity Tyr NO 2 NO 2 H 3 N + -C-H COO- H Amino acids Haptens Lipids Steroids Carbohydrates Proteins Increasing immunogenicity O OH

21. Factors Affecting antigenicity 2- Molecular Weight - Molecular Weight of 10.000 KDa or higher is a good antigen - Molecules small than 5 KDa are not able to induce immune response. 3- Physical Form - In general particulate antigen are more immunogenic than soluble ones . - Denatured antigen are more immunogenic than the native form

22. Factors Affecting antigenicity 4- Route and Dose of Administration - In general ,the subcutenaous route is better than the intravenous or intragastric routes. -There is a dose of antigen above or below which the immune response will not be optimal. 5- Age - Age can also influence immunogenicity. Very young and the very old have diminished ability to elicit and immune response. 6-Genetic Factors . Some substances are immunogenic in one species but not in another and also different from person to another ( responders and non responders) . - The species or individual may lack or have altered genes that code for the receptors for antigen on B cells and T cell

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