A substance most possess the following three characteristics to be immunologic.
2) High Molecular weight
3) Chemical Complexity
4) Solubility (biodegradability)
Animals normally do not respond immunologically to “self”, for example, if a RABBIT is injected with its own serum albumin, it will not mount an immune response. It recognizes the albumin as self. In contrast, if rabbit serum albumin as “foreign” and mount an immune response against it. To prove that the rabbit, which did not respond to its own serum albumin because it recognizes the substance as foreign. Thus, the first requirement for a compound to be immunogenic is foreignness. The substance as foreign. Thus, the first requirement for a compound to be immunogenic is foreignness. The more foreign the substance the more immunogenic it is.
2) High Molecular Weight:
- Compounds that have a molecular weight of less than 1000 daltons are not immunogenic (e.g: Penicillin, Progesterone, Aspirin)
- Compounds that have molecular weight between 1000 and 6000 daltons may (or) may not be immunogenic. (e.g: Insulin, Adrenocorticotropic Hormone (ACTH))
- Compounds that have molecular weight greater than 6000 daltons are generally immunogenic. (e.g: Albumin, Tetanus toxin)
3) Chemical Complexity:
It is necessary for compound to be immunogenic is a certain degree of physiological complexity.
Eg: Homopolymer of Amino Acids, such as
- Polymer of Lysine (mol.wt. 30,000dt)- Seldom is good immunogen
- Poly D-Glutamate (mol.wt. 50,000dt)- It is not immunogen
If the complexity is increased by the attachment of various such as “Dinitrophenol” or other low molecular weight compounds which by themselves are not immunogenic, to be epsilon amino group of polylysine, the entire macromolecule becomes immunogenic.
In general, an increase in the chemical complexity of a compound is accompanied by an increase in its immunogenicity. Thus copolymers of several amino acids such as “polyglutamic acid, Alanine and lysine” are highly immunogenic.
4) Solubility (biodegradability):
Intact antigens must be broken down into immunogenic pieces. Cells must interact with antigens before acquired immunity can induce. Antigen presenting cells (APC) degrade the substances in a manner that enhances the immunogenecity of the antigenic substances, this is called antigenic processing.