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ANTIGENS

ANTIGENS. Antigen: Any substance reacting with the products of any specific immune response (Ig or T cells) Immunogen: Any substance capable to induce a specific immune response All antigens are NOT Immunogenic. For immunogenicity: foreign substance Cemically more complex Larger molecules

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ANTIGENS

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  1. ANTIGENS • Antigen: Any substance reacting with the products of any specific immune response (Ig or T cells) • Immunogen: Any substance capable to induce a specific immune response • All antigens are NOT Immunogenic.

  2. For immunogenicity: • foreign substance • Cemically more complex • Larger molecules are better immunogens (no limit but usually > 6000 Da)

  3. Particulate antigens are better immunogens than soluble antigens • Denaturated antigenes are more immunogenic than the native forms • Easly degradable and phagocytosed antigens are more immonogenic

  4. Host genetic factors influence the immunogenceity. • The age of the hosts influence also the immune response • The dose and route of antigen administration also influence the immune response

  5. Antigens can bind to • B cell receptors • T cell receptors • MHC molecules • Haptens: Small molecules, which are not immunogenic but they induce an immune response when they are attached to a carrier molecule.

  6. Chemically Antigens Can Be • Protein (pure, lipoprotein or glycoproteins) • CH (polysaccharides and lipopolysaccharides) • Nucleic acids * Lipids are not immunogenic but some phospholipids or glycolipids may stimulate T cells

  7. Antigenic determinant or epitope: the portion of the antigen which binds to the the products of a specific immune response

  8. T dependent antigens • They stimulate antibody production with the aid of T cells. - Proteins

  9. T independent antigens • They can directly stimulate B cells without the help of T cells • Pollysaccharides (repeated same antigenic sites) • Type 1 T independent antigenes may activate B cells polyclonally, type 2 NOT

  10. Adjuvants: Enhance the biological effects o an antigen, nonspecifically.

  11. Antigenic determinants recognized by B cells • Linear epitopes: 4-8 amino acid or sugar residues • Conformotional epitopes T cells recognise only amino acid sequences in a protein T cells recognize peptides asscoiated with MHC Antigenic determinants are usually 12-22 amino acids long

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