Agglutination - Introduction, History, Principle, Purpose
Introduction to Agglutination
The word agglutination is derived from the Latin word agglutinare which means glueing to. Hence, in simple terms, agglutination is the clumping of particles. The agglutination reaction includes particles (bacteria or red blood cells) that have been suspended in liquid clumping together to form visible precipitation.
In microbiology, agglutination is used for identification of specific bacterial antigens and subsequent identification of microorganisms. Therefore, agglutination is a vital immune response from the host.
History of agglutination
Bacteriologists Herbert Edward Durham and Max von Gruber are credited for the discovery of specific agglutination in 1896 and the clumping became known as Gruber-Durham reaction. Later on, Gruber derived the word agglutinare from Latin and coined the term agglutinin.
The same year in 1896, French physician Fernand Widal applied the Gruber-Durham’s agglutination test as a test for Typhoid fever. This test is now known as the Widal test.
In 1900 Austrian physician Karl Landsteiner used Gruber-Durham’s agglutination test to discover ABO blood groups. This made blood transfusion safer and provided insight into serology.
Principle of agglutination
Biologically, agglutination is the clumping of particles i.e. an antigen-antibody reaction which occurs when an antigen comes in contact with a corresponding antibody at a suitable pH and temperature.
These antigens are molecules capable of triggering the adaptive immune system. On the other hand, antibodies (also called agglutinins) bind multiple antigens together to form a lattice-like structure that forms clumps by the naked eye. Binding occurs when antibodies bind to the epitomes of one or more bacteria simultaneously.
Antibody and agglutination
The process of agglutination occurs when a specific antibody attaches to the corresponding antigen.
The IgM antibodies are called “cold agglutinins” as they react best at cold temperatures (4 to 22ºC) while IgG antibodies react best at warm temperatures (around 37ºC) and hence are called “warm agglutinins.” Both immunoglobulins bind strongly with complementary antigens.
IgM antibodies, which are large in size are efficiently able to bridge between RBCs to create agglutination. Meanwhile, the IgG antibodies are smaller and require assistance to bridge and form visual agglutination. Such assistance in the detection of IgG is achieved with the help of potentiators.
RBCs have zeta potential i.e. net negative change which causes them to repulse each other. Potentiators function by reducing RBC's zeta potentials. Commonly used potentiators include low ionic strength solution (LISS), albumin, polyethylene glycol (PEG), and proteolytic enzymes.
The ratio of antibodies to antigen must be in proportion for a successful agglutination. If an excess amount of antigens is present, it is called the prozone effect and if antibodies are present in excess amount, it is known as the postzone effect.
In some cases, antibody-antigen complexes are formed but agglutination does not occur. It is due to block antibodies that inhibit agglutination by the complete antibodies added subsequently. Eg: Anti-Rh, anti-brucella antibodies.
Purpose of agglutination
The application/purpose of agglutination is wide and is mostly used in serology and blood typing.
Detect specific antibodies or antigens in samples (blood, saliva, cerebrospinal fluid). Rapid assays use agglutination as a diagnosis for bacterial or viral infections. E.g. – Widal test.
Haemagglutination is used in hemagglutination assay (HA) and the hemagglutination inhibition assay (HI).
Levels of viruses, bacteria, or antibodies in the samples can be measured.
Identification of stains of microorganisms in microbial cultures/isolates.
It is crucial is rapid blood typing where the donor and recipient’s blood is typed and crossmatched to prevent hemolytic transfusion reaction, which is fatal. The antibodies react with incorrectly transfused blood groups resulting in red blood cells clumping together. Each small particle coalesces suspended in the liquid to form larger masses and precipitation occurs.
Determines the presence of Rh factor on the surface of RBC which further classifies blood types into Rh positive or Rh negative.
In sperm quality evaluation and cryopreservation by testing for antibody coating of spermatozoa.
Biological types of agglutination
In biology, agglutination is mainly of two types:
Presence of antibodies, complement
This includes agglutination reaction of cells such as red blood cells or bacteria in the presence of complement or antibody. The host immune system, such as antibodies, binds multiple foreign particles together creating a large complex.
This action increases the efficiency of microbial eliminations by the process of phagocytosis since large clumps of foreign particles can be eliminated at once in comparison to the elimination of individual foreign agents.
Blood typing
Agglutination also occurs in cases of blood transfusion of the wrong blood group. The antibodies react with incorrectly transfused blood groups resulting in red blood cells clumping together. Each small particle coalesces suspended in the liquid to form larger masses and precipitation occurs.