Lec. 8 .ppt.pdf

ANTIGENS Definition of pathogens and types of antigens and antigenic determinants Dr. Sultan Alsharif & Dr. Iman Thabet  Pathogen & antigen? Pathogen: A biological infectious agent that c...

ANTIGENS Definition of pathogens and types of antigens and antigenic determinants Dr. Sultan Alsharif & Dr. Iman Thabet  Pathogen & antigen? Pathogen: A biological infectious agent that causes disease or illness to its host. Ags can be: 1. Foreign substances like micro organisms & its products, toxins etc. 2. Body’s own proteins, expressed in an inappropriate manner like tumor cells, transfused blood or the cells of transplanted organs Immunogenicity – Induction of immune response Dr. Sultan Alsharif & Dr. Iman Thabet Dr. Sultan Alsharif & Dr. Iman Thabet0  Recognition of an Antigen Bacteria or viruses contain Ags both on their surface and inside the cell. Ags are recognized by 1. T cells 2. B cells The T cells require the protein to be ingested, degraded and presented on the surface of a special cell called Antigen Presenting Cell (APC). The processed Ags are presented along with MHC Dr. Sultan Alsharif & Dr. Iman Thabet Dr. Sultan Alsharif & Dr. Iman Thabet0 Dr. Sultan Alsharif & Dr. Iman Thabet 0 Dr. Sultan Alsharif & Dr. Iman Thabet  Classification of Antigens Based on 1. Immunogenicity 2. Origin 3. Source 4. Biological classification Dr. Sultan Alsharif & Dr. Iman Thabet Dr. Sultan Alsharif & Dr. Iman Thabet0  1. Immunogenicity Complete Ag - Able to induce Ab formation. Hence called as IMMUNOGENS. Haptens / Incomplete Ag - small molecule that stimulates the production of antibody molecules only when conjugated to a larger molecule hapten + carrier complete antigen (Immunogen) Dr. Sultan Alsharif & Dr. Iman Thabet Dr. Sultan Alsharif & Dr. Iman Thabet0  2. Origin of Antigens Exogenous Ags – from outside enter the body by inhalation, ingestion or injection. these are taken by the APCs and degraded into small peptides. APCs then present them to helper T cells by using MHC type II molecules. Endogenous Ags – generated within the cell as a result of normal cell metabolism, or because of viral or intracellular pathogenic infection. The fragments are presented along with MHC type I molecules to cytotoxic T cells. Dr. Sultan Alsharif & Dr. Iman Thabet Dr. Sultan Alsharif & Dr. Iman Thabet0  Epitope or Antigenic determinant Small area/ part on the Ag which combines with the specific Ab or T cell receptor. Dr. Sultan Alsharif & Dr. Iman Thabet Dr. Sultan Alsharif & Dr. Iman Thabet0  Determinants of Antigenicity Properties which make a substance antigenic, some of them: 1. Size 2. Nature of Ag 3. Foreignness 4. Susceptibility to tissue enzymes. 5. Exposure to the Ag 6. Adjuvants 7. Antigenic Specificity Dr. Sultan Alsharif & Dr. Iman Thabet Dr. Sultan Alsharif & Dr. Iman Thabet0  1. Size Large molecules are highly antigenic. Low mol.wt. (