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Antigens; chemical and molecular nature; haptens :

Antigens; chemical and molecular nature; haptens


Antigens Substances - BCR - TCR when complexed with MHC Immunogenicity - capable of eliciting HI or CMI response or both B cells – 1) Effector B cells ( Plasma cells ) 2) Memory B cells T cells – 1) Effector T cells ( CTL, T H ) 2) Memory T cells Immunogen instead of antigen


Antigens Antigenicity - Combine with the final products (CSR or Abs) “All immunogens are antigens but not all antigens are immunogens” Haptens are antigenic - Not immunogenic


Immunogenicity Infectious agents - Macromolecules - Proteins - Polysaccharides CMI response - Proteins, lipids and glycolipids - Proteins – peptides + MHC Not an intrinsic property Nature of the immunogen Nature of the biological system

Nature of the immunogen:

Nature of the immunogen Foreignness Molecular size Chemical composition & heterogeneity Susceptibility to antigen processing and presentation

Nature of the biological system:

Nature of the biological system i. Genotype of the recipient animal ii. Immunogen dosage & route of administration iii. Adjuvants


Epitope Immune cells - entire molecule Discrete sites on the molecule - antigenic determinants or epitopes Immunologically active sites - CSR on lymphocytes & antibodies Protein immunogens - Elements of I, II, III, IV structures Polysaccharide - branched chains - multiple chains - conformation

Antigen recognition:

Antigen recognition

Antigen recognition:

Antigen recognition

Carbohydrate antigen:

Carbohydrate antigen Glycolipids – Bacterial cell wall component Capsular polysaccharide - T cell independent (can not be boosted) - T cell dependent (Carrier protein) - improved immunogenicity - boosted antibody titers Glycoconjugate vaccine Glycoproteins – Blood group antigen


Hapten Molecule - < 5 KDa size Poorly immunogenic Immunogenic by covalent linking Carrier proteins – BSA, HSA, KLH, Thyroglobulin, Tetanus toxoid, Diphtheria toxoid Hapten – Carrier conjugate Immune response - Hapten & carrier protein “Drugs, peptide hormones and steroids”

Hapten – carrier conjugate:

Hapten – carrier conjugate