Agglutinins

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. 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.