VMC 221: Veterinary Immunology and Serology (1+1)

Viral haemagglutination (HA) and haemagglutination inhibition (HI)

VIRAL HAEMAGGLUTINATION AND HAEMAGGLUTINATION INHIBITION

• Some viruses can bind and agglutinate mammalian and avian species of RBCs. This assists in characterization of unknown viruses. 
• Specific antibodies against the virus inhibit haemagglutination. This is called haemagglutination inhibition (HI). Hence HI can be used for accurate identification of different haemagglutinating viruses and also to determine levels of antibodies to haemagglutinating viruses. Examples of haemagglutinating viruses are Newcastle Disease virus, Egg Drop Syndrome virus, canine parvo virus, rabies virus etc.
• Bifunctional antibodies: It is made by breaking the bonds between the two heavy chains so that two identical halves are formed. Then two halves from different immunoglobulins are joined to produce a molecule that can cross link two different epitopes. Eg: when a bifunctional antibody, one half of which is directed against dog RBCs and other half against adult heart worm (Dirofilaria immitis) is mixed with whole blood from a heartworm infected dog, it cross links the heartworm antigen to RBCs resulting in visible haemagglutination in a few minutes.