Agglutination (biology)

Agglutination is the clumping of particles. The word agglutination comes from the Latin agglutinare, meaning "to glue."

This occurs in biology in three main examples:
 * 1) The clumping of cells such as bacteria or red blood cells in the presence of an antibody. The antibody or other molecule binds multiple particles and joins them, creating a large complex.
 * 2) The coalescing of small particles that are suspended in a solution; these larger masses are then (usually) precipitated.
 * 3) An allergic reaction type occurrence where cells become more compacted together to prevent foreign materials entering them. This is usually the result of an antigen in the vicinity of the cells.

Hemagglutination
Hemagglutination is when the particles involved are red blood cells. The agglutin is called hemagglutinin.

In cross-matching, agglutination occurring when donor red blood cells and recipient's serum or plasma are incubated together indicates that the donor blood is incompatible for that particular recipient.

Leukoagglutination
Leukoagglutination is when the particles involved are white blood cells.

An example is the PH-L form of phytohaemagglutinin.

Agglutination in microbiology
Agglutination is commonly used as a method of identifying specific bacterial antigens, and in turn, the identity of such bacteria. Because the clumping reaction occurs quickly and is easy to produce, agglutination is an important technique in diagnosis.

History of discoveries
Two bacteriologists, Herbert Edward Durham (-1945) and Max von Gruber (1853–1927), discovered specific agglutination in 1896. The clumping became known as Gruber-Durham reaction. Gruber introduced the term agglutinin (from the Latin) for any substance that caused agglutination of cells.

French physician Fernand Widal (1862–1929) put Gruber and Durham's discovery to practical use later in 1896, using the reaction as the basis for a test for typhoid fever. Widal found that blood serum from a typhoid carrier caused a culture of typhoid bacteria to clump, whereas serum from a typhoid-free person did not. This Widal test was the first example of serum diagnosis.

Austrian physician Karl Landsteiner found another important practical application of the agglutination reaction in 1900. Landsteiner's agglutination tests and his discovery of ABO blood groups was the start of the science of blood transfusion and serology which had made transfusion possible and safe after a while.