Agglutinin
From Wikipedia, the free encyclopedia
An agglutinin is a substance in the blood that causes particles to coagulate and aggregate; that is, to change from fluid-like state to a thickened-mass (solid) state.[1]
Agglutinins can be antibodies that cause antigens to aggregate by binding to the antigen-binding sites of antibodies. Agglutinins can also be any substance other than antibodies, such as sugar-binding protein lectins.
When an agglutinin is added to a uniform suspension of particles, such as bacteria or blood, in a test tube (in vitro), agglutinin binds to the agglutinin-specific structure on the particle causing the particles to aggregate and fall to the bottom, leaving a clear suspension. This phenomenon known as agglutination is of great importance in medicine, as it serves as a diagnostic tool.[2]
Reaction of particles with agglutinin is used to indicate present or past host contact with a pathogen. A host infected with a pathogen produces antibodies to neutralize the pathogen. As a result, the blood of a host applied to a diagnostic kit causes the aggregation of the pathogenic particles due to the antigen-agglutinin interaction. Conversely, agglutination can also be used to identify new bacteria or cells with a specific antigen by exposing them to serum containing known agglutinins.[citation needed]
Agglutination, using blood agglutinins known as hemagglutinins, is used diagnostically to identify blood types of human beings based on the reaction between the erythrocyte (red blood cell) antigens and agglutinins.[2] Human erythrocytes have two main types of antigens (Antigen A and B) expressed in different combinations to give either erythrocytes that express only antigen A, antigen B, antigen A and B together or no antigen at all. When erythrocytes are exposed to hemagglutinins (anti-A and Anti-B antibodies), those expressing antigen A or B coagulate upon contacting anti-A and anti-B hemagglutinins respectively. Erythrocytes expressing both antigens coagulate upon contacting either anti-A or anti-B hemagglutinins while those not expressing any antigen do not coagulate upon contact with any hemagglutinin.[3] This technique serves as a quick and effective method for identifying the blood type of a person and it is essential when blood transfusion has to be performed quickly to replenish lost blood.
