Antigens (Ags)

An antigen is any substance/molecule that can induce/provoke a specific immune response

Complete antigens have two functional properties:
1) Immunogenicity – the ability to stimulate the proliferation of specific lymphocytes and the formation of specific antibodies
2) Reactivity – the ability to react with these lymphocytes and antibodies

Many foreign molecules can act as antigens – proteins, nucleic acids, lipids, polysaccharides, pollen, grains, micro-organisms

Hapten/incomplete antigen:
• reactive but not immunogenic

Antigenic determinants:
• ability of molecule to act as an antigen depends on size and complexity –only specific parts of an entire antigen are immunogenic – this site is the antigenic determinant

Self antigens:
• outside of cells are coated with large protein molecule – these self antigens are not recognised as foreign or antigenic
• some of these are specific proteins are called MHC proteins (coded for by the major histocompatibility complex)

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