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complement deviation 188 complement inhibitor
of interest are revealed by the uptake of dye by the fatally
injured cells.
complement deviation (Neisser–Wechsberg phenomenon)
Blocking of complement fixation or of complement-induced
lysis when excess antibody is present. There is deviation of
the complement by the antibody.
complement fixation assay
A serologic test based on the fixation of complement by
antigen–antibody complexes. It has been applied to many
antigen–antibody systems and was widely used earlier as a
serologic test for syphilis.
complement fixation inhibition test
An assay in which a known substance prevents interaction
of antibody and antigen, thereby preventing complement
uptake and fixation.
RBC
Sheep RBC
with attached
hemolysin
Patient serum +
+
heated to 56°C Antigen
No antibody
C
RBC C
Complement fixation.
RBC
C
+ Unbound
complement
LYSIS
Negative reaction
Complement
Antibody present
NO LYSIS
Positive reaction
Complement fixation.
complement fixation reaction
The primary union of an antigen with an antibody in the
complement fixation reaction takes place almost instantaneously
and is invisible. A measured amount of complement
Ab
C
Complement
RBC
Complement activation.
All
complement
consumed
present in the reaction mixture is taken up by complexes of
antigen and antibody. The consumption or binding of complement
by antigen–antibody complexes serves as the basis for
a serologic assay in which antigen is combined with a serum
specimen suspected of containing the homologous antibody.
Following the addition of a measured amount of complement,
which is fixed or consumed only if antibody is present in the
serum and has formed a complex with the antigen, sheep red
blood cells sensitized (coated) with specific antibody are added
to determine whether or not complement has been fixed in the
first phase of the reaction. Failure of the sensitized sheep red
blood cells to lyse constitutes a positive test, as no complement
is available. However, sheep red blood cell lysis indicates that
complement was not consumed during the first phase of the
reaction, implying that homologous antibody was not present
in the serum and complement remains free to lyse the sheep
red blood cells sensitized with antibody. Hemolysis constitutes
a negative reaction. The sensitivity of the complement fixation
test falls between that of agglutination and precipitation.
Complement fixation tests may be carried out in microtiter
plates, which are designed for the use of relatively small volumes
of reagents. The lysis of sheep red blood cells sensitized
with rabbit antibody is measured either in a spectrophotometer
at 413 nm or by the release of 51 Cr from red cells that have
been previously labeled with the isotope. Complement fixation
can detect either soluble or insoluble antigen. Its ability to
detect virus antigens in impure tissue preparations makes the
test still useful in diagnosis of virus infections.
complement fixing antibody
An antibody of the immunoglobulin G (IgG) or IgM class
that binds complement after reacting with its homologous
antigen. It represents complement fixation by the classic
pathway. Nonantibody mechanisms and IgA fix complement
by the alternative pathway.
complement inhibitor
Protein inhibitor that occurs naturally and blocks the action
of complement components; the group includes factor H,
factor I, C1 inhibitor, and C4-binding protein (C4BP). Also
included among complement inhibitors are heating to 56°C
to inactivate C1 and C2; combining with hydrazine and