Question

What is Hemagglutination Assay?

Answer 1

In the presence of some enveloped viruses, such as the influenza virus, hemagglutination is a reaction that causes red blood cells to clump together. Hemagglutinin, a glycoprotein on the viral surface, interacts with red blood cells, causing red blood cells to clump together and form a lattice.

Complete answer:
Red blood cells precipitate at the bottom of a container in the absence of an enveloped virus, forming a red-colored dot. Red blood cell clumps, on the other hand, disperse in the presence of a virus, leaving no red-colored dot. A hemagglutination assay works on this principle.
It is the most widely used indirect method of virus particle counting. Viruses bind to the surface of RBCs in a variety of ways (red blood cells). When the virus to cell ratio is high, virus particles can attach to red blood cells and form a network that settles out of suspension or agglutinates. RBCs are mixed with a variety of virus preparation dilutions, and each mixture is tested separately.
Hemagglutination is a widely used influenza virus detection and titration assay. One of the major advantages of this assay is that it does not necessitate the use of specialized equipment. Although it has a lower sensitivity, the assay can be used to detect viruses reliably and quickly.
Antibodies developed against a virus are detected and titrated using the hemagglutination inhibition assay (HIA). To detect the presence of antibodies in a given sample, HIA looks for the absence of hemagglutination.
Thus, Hemagglutination Assay is, In the presence of some enveloped viruses, such as the influenza virus, hemagglutination causes red blood cells to clump together. Hemagglutinin, a glycoprotein on the viral surface, interacts with red blood cells, causing them to clump together and form a lattice.

Note:
Red blood cells from sheep, chicks, or humans are coated with antigen and incubated with biological samples to detect the presence of corresponding antibodies in a passive hemagglutination assay.