Final answer:
The hemagglutination assay and indirect hemagglutination inhibition assay are methods used to quantify viruses and detect specific antiviral antibodies in the serum, key for assessing viral infections and immunity.
Step-by-step explanation:
The hemagglutination assay (HA) is a biological technique used to estimate the amount of virus present in a sample, typically for purposes such as measuring viral titer in cell culture or for vaccine production. An indirect assay, specifically the hemagglutination inhibition assay (HIA), is used to determine the presence of antiviral antibodies in a patient's serum. During an HA, a serial dilution of the virus-rich sample is made, and the highest dilution causing visible agglutination of red blood cells indicates the viral titer. If antiviral antibodies are present, as in the HIA, they will prevent the virus from agglutinating the red blood cells, demonstrating the antibody titer based on the highest dilution that inhibits agglutination.
Furthermore, this method is often utilized for detecting pathogenic viruses such as influenza, mumps, and rubella. Viruses produce hemagglutinins that can cause agglutination of erythrocytes, which is visible and indicative of their presence. However, this technique doesn't always distinguish between infectious and noninfectious viral particles, as both can cause hemagglutination.
The direct Coombs' test, another variation of the direct assay, involves using a Coombs' reagent to detect antibodies that facilitate red blood cell agglutination in the presence of certain viruses and bacteria.