Antigen and Factors Affecting Immunogenicity

By Acharya Tankeshwar •  Updated: 05/22/22 •  5 min read

The substance that induces a specific immune response and subsequently reacts with the products of a specific immune response is called an antigen (it is more appropriately called an immunogen). In the case of infectious diseases, antigens are components of invading microorganism structures that are usually composed of proteins or polysaccharides.

Ag has to be recognized by the

Among the biological macromolecules, protein is the most potent immunogen followed by the polysaccharide. Other macromolecules such as lipids and nucleic acids do not serve as immunogens.

For cell-mediated immunity only proteins and some lipids/glycolipids serve as immunogen.

Properties of an Immunogen

Immunogenicity: Ability to induce a humoral and/or cell-mediated immune response.

Antigenicity: The ability to combine/react specifically with the final products of the above responses (i.e., antibodies and/or cell-surface receptors).

All molecules that have the property of immunogenicity also have the property of antigenicity but Reverse not true. Remember: All Immunogen are Antigen but all Antigen are not Immunogen e.g. Hapten.

A hapten is antigenic but incapable by itself of inducing a specific immune response, i.e., it lacks immunogenicity

Epitopes

Hapten

Factors influencing Immunogenicity

Nature of the Immunogen

  1. Foreignness
  2. Molecular size
  3. Chemical composition and heterogeneity
  4. Ability to be  processed and presented with an MHC molecule on the surface of Antigen Presenting Cells (APCs) or altered self-cell

The biological system that the antigen encounters

  1. The genotype of the recipient animal
  2. Dosage and route of administration

Ⅰ. 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.

e.g. If Bovine serum albumin (BSA) is injected into cow, rabbit, and chicken, the order of Immunogenicity will be:

        Cow < Rabbit < Chicken (least for cow and most for chicken)

This property is governed by Tolerance to self (specific unresponsiveness to self-antigens)

Ⅱ.  Molecular Size

A correlation exists between the size of the macromolecule and its immunogenicity

1.Molecular Mass  ≥ 1,00,000 Da:  Active Immunogens
2. Molecular Mass 5000-10,000 Da: Poor immunogen

Exceptions: Few substances with molecular mass less than 1000 Da have proven to be immunogenic.

III. Chemical Composition and Heterogeneity

IV. Susceptibility to Ag Processing and Presentation

The development of both humoral and cell-mediated immune responses requires the interaction of T cells with Ag that has been processed and presented together with MHC molecules.

Contribution of the Biological System

  1. Age: Usually the very young and the very old have a diminished ability to mount an immune response in response to an immunogen.

2. Genotype of the recipient animal

Immunogen Dosage and Route of Administration

A: Amount of Immunogen 

B: Times

Primary Vs. Secondary Immune Response

C. Routes of Administration

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

2 responses to “Antigen and Factors Affecting Immunogenicity”

  1. Pham Khan says:

    Hello Assistance professor ! I need you to allow me to print this Note for due reason to Down load and print out , why is not printable ?

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