the indicator system. • However, if there is antibody in the patient’s serum, there will be no antigen-antibody complex, and therefore, complement will be present free or unfixed in the mixture. • This unfixed complement will now react with the antibody-coated sheep red blood cells to bring about their lysis. • Thus, no lysis of sheep red blood cells (positive CFT) indicates the presence of antibody in the presence of antibody in the test serum, while lysis of sheep red blood cells (Negative CFT) indicates the absence of antibody in the serum.
Positive Test At 37°C Complement gets fixed Step 1: Antigen + Antibody + Complement (from serum) 1 Hour At 37°C Step 2: Fixed Complement complex + Haemolytic system 1 Hour No Haemolysis (Test Positive)
Negative Test Step 1: At 37°C Antigen + Antibody absent + Complement Complement not fixed 1 Hour At 37°C Step 2: Free Complement + Haemolytic system 1 Hour Haemolysis (Test Negative)
Results and Interpretations: No haemolysis is considered as a positive test . haemolysis of erythrocytes indicative of a negative test . 1 2 3 4 A B Microtiter plate showing Haemolysis (Well A3, A4 and B4) and No Haemolysis (Well)
Serum Neutralization Test
Principle of serum neutralization test Neutralization : A procedure in which biological activity of toxin or a living organism is inhibited, usually by a specific neutralizing antibody. In vitro neutralization test: The serum sample or solution of antibody to be tested is diluted and mixed with a viral suspension or toxin. This is incubated to allow the antibody to react with the virus or toxin.
- Fall '15
- antigen-antibody complex