An antibody-antigen complex is a chemical interaction betweenantibodiesandantigens. This complex is also called an immune complex. The chemical interaction takes place between theepitopeon the antigen and the抗体结合部位on the antibody. Weak, noncovalent bonds such aselectrostatic interactions, Van der Waals forces, hydrophobic interactions and hydrogen bondsare involved in the formation of the antibody-antigen complex. The strength of this complex is characterized by two parameters:affinity and avidity.

Figure 1:Antibodies binding to their corresponding antigen on the surface of a pathogen.