hemagglutinationsinhibition

Hemagglutination inhibition, often abbreviated as HI, is a serological assay used to detect and quantify antibodies against a specific antigen, particularly in the context of viruses. The principle of the test relies on the ability of certain viruses, such as influenza viruses, to agglutinate red blood cells (RBCs). Agglutination is the clumping of RBCs.

In a standard HI assay, a known concentration of virus is incubated with a serial dilution of serum suspected to contain antibodies against that virus. If antibodies are present, they will bind to the viral particles, forming antigen-antibody complexes. These complexes are no longer capable of binding to and agglutinating red blood cells.

Following the incubation of the virus and serum, a suspension of red blood cells is added to each well of a microplate. If antibodies are present in a particular serum dilution, the virus will be neutralized, and the RBCs will remain dispersed in the bottom of the well, forming a uniform layer. However, if the antibodies are absent or present at too low a concentration, the virus will bind to the RBCs, causing them to clump together and settle in a pattern across the bottom of the well.

The hemagglutination inhibition titer is defined as the reciprocal of the highest dilution of serum that completely inhibits hemagglutination. This titer is a measure of the antibody level against the specific virus. HI assays are widely used in virology for diagnosing viral infections, studying viral evolution, and assessing vaccine efficacy.