Stages Involved in Antigen-antibody Reactions
The reaction between antigen and antibody occurs in three stages.
The primary stage is the initial reaction between the two, without any visible effects. This reaction is rapid, occurs even at low tempera-tures and obeys the general law of physical chemistry and thermody-namics. The reaction is reversible, the combination between antigen and antibody molecules being effected by the weaker intramolecular forces such as vander waals forces, ionic bonds and hydrogen bonding rather than by the firmer covalent bonding. The primary reaction can be detected by estimating free and bound antigen or antibody sepa-rately in the reaction mixture.
The secondary stage leads to demonstrable events such as pre-cipitation, agglutination, lysis of cells, killing of live antigens, neutral-ization reactions, complement fixation and enhancement of phagocy-tosis.
Thus the antigen causing Agglutination was called agglutinin that causing precipitation precipitin.Thus the antibody causing agglutination was called Agglutinogen, that causing precipitin precipitinogen.
Some antigen-antibody reactions occurring in vivo initiate chain reactions that lead to neutralization or destruction of injurious antigens, or to tissue damage. These are the tertiary reactions and include hu-moral immunity against infectious disease as well as clinical allergy and other immunological diseases.