1Immunological Tests

• 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.

2Precipitation tests

• 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.

3Immunoelectrophoresis

http://www.bio.txstate.edu/~micro/IEP%20%2204.jpg

4Agglutination

• 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 produce a negative test:• Titer.

Blood typing: yes/no example of agglutination

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5Agglutination-2

• 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/images/testID11/Figure01.jpg

Commonly used for quick tests to identify staph, strep, many others.

6Fluorescent antibody tests

• Specific antibody attached

to fluorescent dye.

antibody binds to antigens,

Use of fluorescent scope

reveals positive cells.

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.

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7Enzyme linked immuno sorbent assay

http://www.biosystemdevelopment.com/site_graphics/elisa.jpg

8ELISA-2

• 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.