Covers the definitions of antigens and immunogens and the idea of immunogenicity, then the chemical nature of antigens and the blood-group example of ABO and Rh. It goes on to factors that make a substance immunogenic, linear and conformational epitopes, and exogenous versus endogenous antigens with their MHC presentation. The note also classifies alloantigens, autoantigens and tumour antigens, and closes with adjuvants, including Freund's adjuvant and its complete and incomplete forms.
Topic 37 of 63 in the MU Pleven syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 10 sections, about 439 words (3 min of reading), with 14 flashcards.
In this note
Immunogens and antigens – characteristics.
Functions & Nature of Antigens
Factors Influencing Immunogenicity
Epitopes & Antigen Specificity
Classification of Antigens
Alloantigens
Autoantigens
Tumor Antigens
Vaccines & Adjuvants
Adjuvants
Immunogens and antigens – characteristics.
An antigen is any substance that can be specifically recognized and bound by components of the immune system such as antibodies or lymphocytes.
An immunogen is an antigen capable of inducing a humoral and/or cell-mediated immune response (rather than tolerance).
→ This ability is called immunogenicity.
Functions & Nature of Antigens
Antigens are usually proteins or polysaccharides. They bind to specific antibodies, allowing the immune system to detect and neutralize harmful foreign substances.
In human blood groups, the letter (A, B, AB, O) reflects the specific antigen on RBC surfaces.
All groups contain the basic O antigen.
A antigen carries N-acetylgalactosamine.
B antigen carries galactose.
AB expresses both.
The enzymes responsible for modifying the oligosaccharide chains differ slightly, demonstrating antigen specificity.
Rh factor (+/–) is due to the presence or absence of additional antigens.
Factors Influencing Immunogenicity
Foreignness: Antigens must be non-self, since self-reactive lymphocytes are deleted during development.
