Antigen and Antibody Interaction

Antibodies produced by B cells bind specifically and non-covalently to their exclusive antigens that induced their production.

The substance that has been formed as a result of antigen antibody interaction is known as “immune complex” or “antigen antibody complex”.

Various reversible, non covalent interactions between antigenic determinants and antibody variable regions are responsible for the formation of immune complex. Intermolecular interactions between side chains of epitope subunits and those of the paratope include these nop covalent interactions. Immune complex formation is the basis for humoral immunity or antibody mediated immune response.


Chemical Basis of Antigen Antibody Interaction

When an antibody and its specific antigen come close to each other they interact through the chemical groups established on the surface of epitope and paratope.

The bond between them is exclusively noncovalent. The major bonds formed between antigen and antibody is hydrophobic in nature. Many of the nonpolar side chains of proteins are hydrophobic in nature. When antigen antibody molecules come close to each other, these side chains interact and exclude water molecules from the area of interaction.

Displacement of water molecules increases the binding force of interacting Ag – Ab molecules and the complex becomes energetically stable. If the non covalent bond between antigen and antibody is mediated through hydrogen bonds, both epitope and paratope share hydrogen. Major hydrogen bonds formed in Ag and Ab interaction are


O-H-O, N-H-N and O-H-N.

Even though Van der Waals force between two atoms is very weak, it may become collectively important in immune complex formation.