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

PASSIVE HAEMAGGLUTINATION

• Since agglutination is a much more sensitive technique than precipitation, it is sometimes useful to convert a precipitating system to an agglutinating one.
• In passive haemagglutination, antigen coated red blood cells are prepared by mixing a soluble antigen with RBCs that have been treated with tannic acid or chromium chloride, both of which promote adsorption of antigen to the surface of the cells.
• The antigen coated RBCs are agglutinated by specific antibody to the adsorbed soluble antigen.
• In the actual test, serum containing antibody is serially diluted into microtitre plate wells and the antigen coated RBCs are than added to each well.
• Wells showing a layer of uniformly agglutinated cells on the bottom of the well are positive.
• In negative reaction, compact sharply demarcated discs of sedimented cells are seen at the bottom of the well.
• Passive haemagglutination is used for assessing the antibody titre in vaccination against Pasteurellosis.