There is a freely reversible equilibrium between dissociation and reformation of the Ab-virion complex.decreasing the concentration of the reactants diminishes the rate of complex formation but not the rate of dissociation. With time the antibody virus complexes become more stable. If the assay is made several hours after the virus has been mixed with the antibody, neutralization persists even after dilution. Whereas reversible complexes form readily at 0 c,with little temperature dependence,the formation of irreversible complexes occur at 37, suggesting the need for configurational changes. Specific for viruses that hemagglutinate.
Antibody blocks specific antigen on the virus surface that is responsible for hemmaglutination.
In influenza note two proteins on the surface,hemagglutinin and neuraminidase. The test is done exactly as hemagglutination except add 560C inactivated immune serum, then virus, then red blood cells, with dilution of the serum. Simple, inexpensive test, used clinically. 3 .Gel immunodiffusion and Immunoelectrophoresis. Antibody and soluble antigen diffuse toward one another through agar and produce visible lines of precipitate where homologous antibody and antigen meet in the gel.