Immunogen
Definition
A molecule that is both immunogenic (triggers antibody production) and antigenic (binds those antibodies). Used interchangeably with 'complete antigen'. Most protein antigens and polysaccharide antigens above a molecular weight threshold of roughly 5,000 to 10,000 Da qualify as immunogens.
- Synonym
- Complete antigen
- Requires
- Immunogenicity and antigenicity both
- Typical MW threshold
- Roughly 5,000 to 10,000 Da
- Contrast
- Hapten, antigenic but not immunogenic alone
Common questions
How is an immunogen different from a hapten?+
A hapten is small and antigenic, meaning it can bind antibodies, but cannot trigger antibody production on its own; it must be conjugated to a larger carrier protein to become immunogenic, whereas a full immunogen does both jobs unaided.
Why does molecular weight matter for whether something is an immunogen?+
Below roughly 5,000 to 10,000 Da, most molecules are too small for the immune system to process and present effectively, so they tend to function as haptens rather than complete immunogens.
Related terms
- Antigen
- A molecule recognised by the adaptive immune system through specific binding to an antibody or T-cell receptor. Defined by immunogenicity (capacity to...
- Cross-Reactivity
- The capacity of an antibody raised against one analyte to bind structurally related compounds. In RIA, cross-reactivity is the main driver of...
- Epitope
- The specific region of an antigen that makes physical contact with an antibody's binding site (paratope). Also called the antigenic determinant. A...
- Hapten
- A small molecule with antigenicity but no immunogenicity on its own. Haptens must be conjugated to a carrier protein to raise antibodies....
- Secretor Status
- A genetic trait that determines whether a person expresses their ABO blood group antigens in secreted body fluids such as saliva, semen,...