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

COMPLEMENT FIXATION TEST

• The activation of the complement system by antiserum bound to antigen results in the generation of membrane attack complexes that can disrupt cell membranes.If the antibody is bound to RBC, then hemolysis occurs. This phenomenon can be used to measure serum antibody levels in a test called the complement fixation test.
• First the antigen and serum under the test (heated to 56°C for 30 minutes to inactivate complement) are incubated in the presence of normal guinea pig serum (it acts as the source of complement).
• After the antigen - antibody - complement mixture reacts, the amount of free complement is measured by adding an indicator system consisting of antibody coated sheep RBCs.
• Lysis of these cells (seen as a transparent red solution) is a negative result since it indicates that complement was not activated and that antibody was absent from the test serum.
• Absence of lysis indicated by a cloudy RBC suspension or button formation indicates that complement was consumed or fixed. This is a positive test.
• This test is applied for the diagnosis of many viral and bacterial diseases. Ex. FMD in animals, Japanese encephalitis in man etc.