Antigen and antibody interaction

The reaction between antigen and antibody is the molecular basis of humoral (antibody-mediated) immunity, and it proceeds in three stages: first, the antigen and antibody physically combine to form an antigen-antibody complex; next, this complex produces a visible event such as precipitation or agglutination; finally, the antigen is destroyed or neutralised. The strength of this binding — called antibody affinity — depends on three factors: how closely the antigen and antibody fit together, the sum of the non-covalent intermolecular forces holding them (hydrogen bonds, electrostatic attraction, Van der Waals forces and hydrophobic interactions — notably, no covalent bonds are involved), and the intrinsic affinity of the particular antibody for that particular antigenic determinant. A close, well-matched fit produces strong binding; a poor fit produces weak binding. …