Immunology for Dummies: Antigens and Antigen Receptors

Part 2: Antigens and Antigen Receptors

What is an antigen?

An antigen is a substance that stimulates the production of antibodies and can be recognised by a B cell receptor or antibody, or a T cell receptor. As mentioned before, the part of the antigen which comes into contact with the antigen receptor is called the epitope or antigenic determinant.

Antibody - A protein that fights infection.

2 types of Epitopes

A linear or a sequential epitope is an epitope that is recognized by antibodies by its linear sequence of amino acids, or primary structure.

In contrast, most antibodies recognize a conformational epitope that has a specific three-dimensional shape and its protein structure. Conformational epitopes are recognised by antibodies. When the molecule is denatured, the epitope is destroyed due to hanges in its 3-dimensional configuration.

Do B and T cell receptors recognise the same antigen?

B cell receptors (antibodies) can recognise both linear and conformational epitopes. Take note that B cell receptors which recognises conformational epitopes (on native molecules) will not recognise the denatured protein.

T cell receptors recognise short linear peptides presented by MHC molecules.

MHC stands for Major Histocompatibility Complex. It is a complex of genes coding for a large family of cell-surface proteins that bind peptide fragments of foreign proteins and present them to T cells to induce an immune response.