Definitions

viral hemagglutination

Hemagglutination

[hee-muh-gloot-n-ey-shuhn, hem-uh-]
Hemagglutination (also haemagglutination) is a specific form of agglutination that involves red blood cells. It has two common uses in the laboratory: blood typing and the quantification of virus dilutions.

Blood Typing

Using antibodies that bind to the A or B blood group in a sample of blood, one can determine the blood type of the individual being tested.

For example, if antibodies that bound to the A blood group were added and agglutination occurred, it could be concluded that the blood was either type A or type AB. Then if antibodies that bound the B group were added and agglutination did not occur, it could be concluded that the blood was type A.

In blood grouping the patient's serum is tested against RBCs of known blood groups and also the patient's RBCs are tested against known serum types. In this way the patient's blood group is confirmed from both RBCs and serum. A direct Coombs test is also done on the patient's blood sample in case there are any confounding antibodies.

Viral Hemagglutination Assay

Many viruses attach to molecules present on the surface of red blood cells. A consequence of this is that - at certain concentrations - a viral suspension may bind together (agglutinate) the red blood cells thus preventing them from settling out of suspension. Usefully, agglutination is rarely linked to infectivity, attenuated viruses can therefore be used in assays.

By serially diluting a virus suspension into an assay tray (a series of wells of uniform volume) and adding a standard amount of blood cells an estimation of the number of virus particles can be made. While less accurate than a plaque assay, it is cheaper and quicker (taking just 30 minutes).

This assay may be modified to include the addition of an antiserum. By using a standard amount of virus, a standard amount of blood cells and serially diluting the antiserum, one can identify the minimum inhibitory concentration of the antiserum (the greatest dilution which inhibits hemagglutination).

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