1. BY:
DR. NEHAL AHMED NOUH

2.  The complement system helps or “complements” the
ability of antibodies and phagocytic cells to clear
pathogens from an organism.
 Thecomplement system consists of a number of small
proteins found in the blood.
 They are generally synthesized by the liver, and
normally circulating as inactive precursors (pro-
proteins) that need stimulation.

3.  The complement fixation test:
Is an immunological medical test that can be
used to detect the presence of either specific
antibody or specific antigen in a patient's serum.
 It was widely used to diagnose infections,
particularly with microbes that are not easily
detected by culture methods, and in rheumatic
diseases.
 Complement fixation is still used to diagnose
some viral, fungal, and rickettsial diseases.

4.  There are two steps:
1- The complement fixation step.
2- The indicator step.
1- Complement Fixation Step:
 Add antigen and complement to serum.
 If the serum contains antibodies against the antigen
they will bind to the antigen and fix the complement.
 This ties up all the free complement so it can't
participate in the next step, the indicator step.

5. 2- Indicator Step:
 Add sheep red blood cells and anti-sheep red blood
cell antibodies to the serum.
 Antibodies to the sheep red blood cells bind and can
fix complement, if any is available.
 The test is considered negative if the solution turns
pink at this point and positive otherwise.

6.  If complement is available it will be fixed by the sheep
red blood cell antigen-antibody complex and the sheep red
blood cells will be lysed.
 This indicates that the serum did not contain antibodies
against the antigen added in the complement fixation step
and complement remained free.
 If no complement is available the sheep red blood cells
will not be lysed.
 This indicates there were antibodies against the antigen
added in the complement fixation step and all the
complement was tied up when it was fixed by the original
antigen-antibody complex.

8.  Anti-streptolysin O is the antibody made against
streptolysin O.
 Streptolysin O: is an immunogenic, hemolytic toxin
produced by most strains of group A and many strains
of groups C and G streptococci.
 The O in the name stands for oxygen-labile.
 The main function of streptolysin O is to cause
hemolysis (the breaking open of red blood cells) in
particular, beta-hemolysis.

9.  Procedure:
 The reagent and sample are both allowed to reach room
temperature.
 On two separate slides, a drop of sample is placed. To one
slide, positive control is added and to the other, negative
control is added.
 Next, a drop of the latex reagent should be added to the
sample that has to be tested.
 Rotate the card for proper mixing for 1-2 minutes and then
observe agglutination i.e. small clumps formation.
 Agglutination indicates a positive ASO test.

11.  In neutralization reactions, the harmful effects of
a bacterial exotoxin or virus are eliminated by a
specific antibody.
 An antitoxin is an antibody produced in response
to a bacterial exotoxin or a toxoid that neutralizes
the exotoxin.

12.  In a virus neutralization test, the presence of
antibodies against a virus can be detected by the
antibodies’ ability to prevent cytopathic effects of
viruses in cell cultures.
 Antibodies against certain viruses can be detected
by their ability to interfere with viral
hemagglutination in viral hemagglutination
inhibition tests.