Antigens

From DrugPedia: A Wikipedia for Drug discovery

Revision as of 06:12, 18 August 2008

Antigen (antibody generating) is a substance that prompts the generation of antibodies that can cause an immune response. Antigens can be

• proteins
• polysaccharides
• conjugates of lipids with

  * proteins (lipoproteins) and
  * polysaccharides (glycolipids)

Antigens that enter the body from the environment would include

• inhaled macromolecules (e.g., proteins on cat hairs that can trigger an attack of asthma in susceptible people) • ingested macromolecules (e.g., shellfish proteins that trigger an allergic response in susceptible people) • molecules that are introduced beneath the skin (e.g., on a splinter or in an injected vaccine)

Antigens that are generated within the cells of the body would include

• proteins encoded by the genes of viruses that have infected a cell • aberrant proteins that are encoded by mutant genes; such as mutated genes in cancer cells

Immunogen

Any substance that can elicit an immune response

• All immunogens are antigens
• Not all antigens are immunogens, i.e. haptens

Immunogenicity of Antigens

Factors determining immunogenicity

• Foreignness
• Molecular Size
• Chemical Composition
• Degradability

Factors influencing immunogenicity

• Host genotype
• Dose and route of administration
• Presence of adjuvants

EPITOPES

• Discrete sites on immunogens recognized by antibodies or T cell receptors
• Macromolecules contain many epitopes with different immunogenicities
• Immunogenicity can vary between individuals and populations.
• Some epitopes are immunodominant