Immunological Tests

Immunological Tests

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• 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

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• 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

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Agglutination-2

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• 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.

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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

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• 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.