Immunological Tests
1
• A harmful agent can be detected
– Toxins, viruses, hard to culture bacteria
– Takes advantage of the specific nature of antibodies
• Rise in amount of antibody is an indicator
– An increase in specific antibody is an indicator of
exposure, can confirm a diagnosis.
• Antibodies bind, precipitate, and agglutinate.
Precipitation tests
2
• When sufficient antigen and antibody molecules
interact, they precipitate out of solution
– Too few antigen molecules, little ppt.
– Too many, agn-aby cross links not made.
• Examples
– immunodiffusion: antibody and antigen react in agar
to make ppt band or ring.
– Immunoelectrophoresis: complex mixture of
antigens separated, then reacted with antibody.
Immunoelectrophoresis
http://www.bio.txstate.edu/~micro/IEP%20%2204.jpg
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Agglutination
• Measuring about of antibody in
patient’s serum
– Dilute serum serially (usually
1:2)
– Mix with known antigen.
Clumping will be visible if
antibody is present. When
antibody is too dilute, clumping
no longer seen.
– The amount of dilution to
Blood typing: yes/no
produce a negative test:
example of
• Titer.
agglutination
classes.midlandstech.com/.../chap18/lecture3.htm
4
Agglutination-2
5
• Identifying pathogens
– Known antibody
against the pathogen is
attached to latex
beads.
– Mixing latex with
bacterium produces
clumping
http://www.medicine.uiowa.edu/cme/clia/i
mages/testID11/Figure01.jpg
Commonly used for quick tests to identify staph, strep,
many others.
Fluorescent antibody tests
• Specific antibody attached
to fluorescent dye.
antibody binds to antigens,
Use of fluorescent scope
reveals positive cells.
6
https:/.../Web_Version/chapters/c
hapter_23.htm
Very valuable tool in specific identification of pathogenic
microbes of all kinds. This is DFA (direct fluor. Aby.).
In IFA, a fluorescent antibody against another antibody
is used.
Enzyme linked immuno sorbent assay
http://www.biosystemdevelopment.com/site_graphics/elisa.jpg
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ELISA-2
8
• This technique can be used to detect antibody
or antigen.
• Attach antigen to the plastic
– Add serum from patient; antibodies attach.
– Antibodies detected with an enzyme-linked antibody
against human antibodies.
• Attach known antibody to plastic
– antigen added, binds to antibody.
– Second, enzyme-linked antibody binds to antigen.