Types of agglutination - Principle, Active, Direct, Indirect Hemagglutination
Introduction to 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.
The precipitation occurs when antibodies act as a bridge to form a lattice network of antibodies and cells that carry the antigen on their surface.
Principle of agglutination
Agglutination occurs when particulate test antigens conjugate to a carrier and react with patient serum which contains specific antibodies to form visible clumps from the formation of antigen-antibody complex. Carriers can be artificial such as charcoal or latex particles or biological such as red blood cells (RBCs).
The quality of agglutination is based on environmental conditions (temperature, pH, and protein concentrations), time of incubation with the antibody source, and amount of antigen conjugated to the carrier.
Types of agglutination
Agglutination tests are easy to perform, have high sensitivity and test results are easily visible to read.
Agglutination reactions can be divided into three groups:
Active/Direct agglutination
Passive Agglutination
Hemagglutination
Active/Direct agglutination
In active agglutination, antigens are found naturally on a particle with which agglutination with specific antibodies occurs. It uses whole pathogens as a source of antigen and also measures antibody levels in a host infected with the specific pathogen. The binding of surface antigens on the bacteria results in visible clumps.
Active agglutination is of the following types.
Slide/Tile agglutination
Tube agglutination-introduction-and-applications
Heterophile agglutination test
Antiglobulin (Coombs) test
Passive agglutination
In passive agglutination, carrier particles are coated with soluble antigens and either antibody or antigen is attached to the specific inert carrier. When antigen or antibody reacts, cells or particles get agglutinated. Inert carriers can be bentonite, latex particles, or carbon particles.
One of the most commonly used passive agglutination is the latex agglutination.
If the antibody is adsorbed on the carrier instead of the antigen, it is called reverse passive agglutination.
Eg: ASO test
Hemagglutination test
Hemagglutination is the process in which red blood cells agglutinate. It is caused by a group of agglutinins called hemagglutinins (receptor-binding membrane fusion glycoproteins) and causes RBC to stick together.
In the hemagglutination test, RBCs of sheep, chicks, or humans are used as biological carrier particles. Purified polysaccharides and proteins can also be used to determine the presence of corresponding antibodies.
In indirect Hemagglutination assay (IHA), RBCs are coated with antigen to detect antibodies in the serum.
If antibodies are attached to RBCs for the detection of microbial antigens, it is called reverse passive hemagglutination (RPHA).
Hemagglutination test includes viral hemagglutination and coagulation test.
Haemagglutination can also occur in the presence of certain dietary lectins such as Phytohemagglutinin (PHA).
Leukoagglutination
Agglutination in which white blood cells are involved is called leukoagglutination. They are found in legumes - highest concentrations in uncooked red kidney beans and white kidney beans. If consumed raw or improperly cooked, its toxicity can cause poisoning in monogastric animals including humans.