An agglutination reaction occurs when specific antibodies cross-link cells or particles to form an immune complex.
Agglutination results when insoluble antigens (such as viral or bacterial cells) are cross-linked by antibody
Agglutination reactions usually create visible clumps or aggregates, called agglutinates, that the naked eye can see.
For the diagnosis of certain diseases direct agglutination reaction is very useful.
For example, the Widal test involves a reaction that agglutinates typhoid bacilli when an individual who has typhoid fever mixes serum containing typhoid antibodies with them.
Uses and application of Agglutination Reaction
Researchers have also developed techniques 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).
Researchers also use latex agglutination tests to detect antibodies that develop during certain mycotic (fungal), helminthic (worm), and bacterial infections, as well as in drug testing.
Researchers can also coat microspheres with monoclonal antibodies to capture antigens from patient specimens.
Hemagglutination Reaction
Antibodies attach to surface antigens, cross-link red blood cells, and result in hemagglutination, which researchers routinely use 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, when researchers mix measles virus particles and red blood cells, hemagglutination occurs.
However, researchers may first mix a person’s serum with virions, followed by adding red blood cells. If no hemagglutination occurs, the serum antibodies have neutralized the measles viruses. Researchers consider this 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.
Researchers widely use hemagglutination inhibition tests 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.
Researchers develop fungal serology to detect the serum antibody, but they limit it to very few fungi.
Researchers use the cryptococcal latex antigen test for the direct detection of Cryptococcus neoformans.
The clinical laboratory uses automated and non-automated methods for the rapid identification of yeasts.
Any serological method used to detect fungi is best go with morphological studies examining for chlamydospores, pseudohyphae and yeast cell structure, and so on.
Researchers also use agglutination tests to measure antibody titer.
In tube or well agglutination tests, a technician adds a specific amount of antigen 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.
Researchers then add serial dilutions of serum (1/20, 1/40, 1/80, 1/160, etc.) containing the antibody to each tube or well.
We determine the greatest dilution of serum showing an agglutination reaction, and the reciprocal of this dilution is the serum antibody titer.
