Page 350 - The Veterinary Laboratory and Field Manual 3rd Edition

Serology and immunology 319

complement fixation test Guinea pig serum is commonly used as the
source of complement for the haemolytic CFT
The fact that antibody, once it combines with as it has a strong ability to lyse RBCs. Activated
antigen, activates complement can be used for (antibody coated) sheep RBCs are usually used
diagnostic purposes. The standard CFT uses as the ‘indicator system’ in this test. In the
sheep RBCs sensitized with rabbit anti-sheep CFT, if specific antibody is present in the test
RBC antibody as an indicator system. In the serum sample, the sheep RBCs do not lyse as
body, the complement cascade is a chain of the antibody interferes with the action of the
chemical reactions which is involved in the con- added guinea pig complement. If antibody is not
trol of inflammation and the immune response. present then the guinea pig complement is avail-
The CFT has the disadvantage that it is difficult able to cause cell lysis. The basis for this test is
to perform. This is largely because it is difficult illustrated in Figure 6.10. The advantage of the
to obtain and standardize the reagents used. test is that it is usually very easy to read the

Figure 6.10 Principle of the CFT. In a positive sample the antigen–antibody reaction binds with the comple-
ment and inhibits the lysis of RBCs in the test sample. Source: M. Sarjoon Abdul-Cader, University of
Calgary, Canada.

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