Agglutination vs Precipitation- Definition, 14 Differences, Examples

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Agglutination Definition

Agglutination is the process of clumping of antigens with their respective antibodies.

• Agglutination reactions are used to particulate test antigens that are usually conjugated to a carrier.
• The carrier can either be artificial (such as latex or charcoal particles) or biological (such as red blood cells).
• The agglutination process involving red blood cells is termed hemagglutination, and the process with white blood cells is termed leukoagglutination.
• These conjugated particles then react with the patient’s serum which might or might not contain antibodies.
• The result of this test can be collected based on the observation of clumps resulting from that antigen-antibody complex formation.
• The sensitivity and accuracy of the result depend on a number of factors like the duration of incubation with the antibody, amount and strength of the antigen conjugated to the carrier, and test conditions like the pH and protein concentration.
• Different forms of agglutination are used in diagnostic tests which include latex agglutination, flocculation tests, direct bacterial agglutination, and hemagglutination.
• Because the process is quick and straightforward, these diagnostic tests are preferred over other sophisticated tests.
• Agglutination has been used for the detection of antigens in bacteria which ultimately helps in the identification of those bacteria.
• A modified and more sensitive technique associated with agglutination is agglutination-PCR.
• In this technique, the antibodies bind and agglutinate with antigen-DNA conjugates which enables the DNA strands to ligate with the antibodies.
• The agglutination formed is then used to quantify the DNA strands by q-PCR.

Precipitation Definition

Precipitation is a process where soluble antigens bind with their specific antibody at an optimum temperature and pH, resulting in the formation of an insoluble precipitate.

• The interaction between the soluble antigen and antibody results in the formation of insoluble lattice that forms precipitate out of the solution.
• The process of precipitation has some requirements involving the valency of both the antigen and the antibody.
• For precipitation to take place, the antibody must be bivalent, and the antigen must be either bivalent or polyvalent.
• Precipitation takes place in the zone of equivalence, where the concentration of antigen and antibody is equal. On either side of equivalence, precipitation doesn’t occur if the concentration of either antigen or antibody is in excess or deficient.
• Immunological techniques like immunodiffusion and electroimmunodiffusion utilize the principle of precipitation reactions.
• The principle of precipitation is also applied in analytical chemistry for the detection of various functional groups of chemical substances.
• If a lighter precipitate is formed, another process, termed flocculation, takes place. In flocculation, the precipitate floats instead of sedimenting.
• Precipitation reactions are commonly performed on semi-solid surfaces like agar media or non-gel support media like cellulose acetate.
• The precipitate formed in the reaction remains suspended until enough force of gravity can settle the precipitate towards the bottom of the surface.

Key Differences (Agglutination vs Precipitation)

Examples of Agglutination

Haemagglutination assay

• Haemagglutination assay is a diagnostic technique used for the detection of viruses, bacteria, and antibodies.
• The antigens present in various viruses or bacteria bind with the sialic acid receptors present on the surface of red blood cells, creating a network of RBCs and viral particles.
• The formation of these lattices depends on the concentration of viruses/ bacteria and RBCs.
• When the concentration of the antigen is too low, the RBCs are not arranged in lattices but settle down at the bottom of the container.
• Haemagglutination is based on the same principle as the one used by viruses during infection.
• Control is placed in one of the wells to compare the concentration of antigen present in the sample.
• Based on the amount of agglutination formed in the well, the concentration of the antigen can be determined. The antigen concentration can then be used to determine the concentration of the organism present in the sample.

Examples of Precipitation

Immunodiffusion precipitation test

• Immunodiffusion is an immunological technique used for the detection and quantification of antibodies and antigens, which are mostly immunoglobulins and nuclear antigens.
• In this technique, antigen and antibodies are applied simultaneously in two adjacent wells.
• As the antigen and antibody diffuse towards each other, precipitates are seen in the form of lines as the antigen and antibodies interact with each other.
• It is also possible to compare the concentration of different antigens by placing multiple antigens in multiple wells.
• Based on the formation of precipitation lines, the presence of different antigens and, in turn, the presence of viruses or bacteria can be detected.

References and Sources

• Judith A. Owen, Jenni Punt, Sharon A. Stranford (2013). Kuby Immunology. Seventh Edition. H. Freeman and Company.
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