Factors:
- Nature of the Immunogen,
- Foreignness ,
- Molecular size,
- Chemical composition and heterogencity
The biological system that the antigen encounters,
The genotype of the recipient animal,
Dosage and route of administration.
1 . Foreignness
Antigens must be recognized as non-self by the biological system.
The degree of immunogenicity depends on the degree of foreignness i.e. The greater the phylogenetic distances between two species, the greater the structural (and therefore the antigenic) disparity between them.
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2. Molecular Size: A correlation exists between the size of the macromolecule and its immunogenicity.
3 . Chemical Composition and Heterogeneity:
Chemical complexity contributes to immunogenicity.
Co-polymers composed of different amino acids or sugars are usually more immunogenic than homopolymers of their constituents.
All four levels of protein organization contribute to the structural complexity of a protein and hence affect its immunogenicity.