An agglutination reaction occurs when an immune complex is formed by cross-linking cells or particles with specific antibodies.
Agglutination results when insoluble antigens (such as viral or bacterial cells) are cross-linked by antibody
Agglutination reactions usually creates visible clumps or aggregates, called agglutinates, that can be seen with the help of naked eye.
For the diagnosis of certain diseases direct agglutination reaction is very useful.
For example, the Widal test is a reaction that involvs agglutination of typhoid bacilli when they are mixed with serum that contains typhoid antibodies from an individual who has typhoid fever.
Uses and application of Agglutination Reaction
Techniques have also been developed that employ microscopic synthetic latex spheres coated with antigens.
These coated microspheres bind antibodies in a patient’s serum specimen to identify viral disease rapidly when cultures are not feasible (e.g., HIV).
Latex agglutination tests are also used to detect antibodies that develop during certain mycotic (fungal), helminthic (worm), and bacterial infections, as well as in drug testing.
Microspheres can also be coated with monoclonal antibodies so as to capture antigens from patient specimens.
Hemagglutination Reaction
Hemagglutination results from antibodies cross linking red blood cells through the attachment to surface antigens and is routinely used in blood typing.
In addition, some viruses can accomplish viral hemagglutination. For example, if a person has a certain viral disease, such as measles, antibodies will be present in the serum to react with the measles virus particles and neutralize them.
Normally hemagglutination occurs when measles virus particles and red blood cells are mixed.
However, a person’s serum may be mixed first with virions, followed by the addition of red blood cells. If no hemagglutination occurs, the serum antibodies have neutralized the measles viruses. This is considered a positive test result for the presence of virus-specific antibodies.
(a) The virions of few viruses can bind to red blood cells, causes hemagglutination.(b) If serum containing specific antibodies to the virus is mixed with the red blood cells, the antibodies will neutralize the virus and inhibit hemagglutination (a positive test).(c)Reovirus hemagglutination test results.
Hemagglutination inhibition tests are widely used to diagnose influenza, measles, mumps, mononucleosis, and other viral infections.
The most routinely used techniques for identification of the mycoplasmas are hemagglutinin reactions, antigen-antibody reactions using the patient’s serum, and PCR.
These microorganisms are slow growing; therefore, positive results from isolation procedures are rarely available before 30 days-a long delay that may put a patient’s life at risk.
Fungal serology is developed to detect the serum antibody but is limited to very few fungi.
For the direct detection of cryptococccus neoformans cryptococcal latex antigen test is used.
fofr the detection of yeasts in the clinical laboratory automated and non-automated methods for rapid identification is used.
Any serological method used to detect fungi is best go with morphological studies examining for chlamydospores, pseudohyphae and yeast cell structure, and so on.
Agglutination tests are also used to measure antibody titer.
In tube or well agglutination tests, a specific amount of antigen is added to a series of tubes or shallow wells in a microtiter plate.
(a)Tube agglutination test for determining antibody titer. The titer in this example is 160 because there is no agglutination in the next tube in the dilution series (1/320). The blue in the dilution tubes indicates the presence of the patient’s serum.(b) A microtiter plate illustrating hemagglutination. The antibody is kept in the wells (rows 1-10). Positive (row 11) and negative controls (row 12) are also kept. Red blood cells are added to each well. If antibody is present to agglutinate the cells, they sink as a mat to the bottom of the well. If insufficient antibody is present, they form a pellet at the bottom.
Serial dilutions of serum (1/20, 1/40, 1/80, 1/160, etc.) containing the antibody are then added to each tube or well.
The greatest dilution of serum showing an agglutination reaction is determined, and the reciprocal of this dilution is the serum antibody titer.
