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Precipitation tests

Precipitation tests. Agar immunodiffusion Lab 5. Serological Tests. Precipitation tests Antigen/Ab conjugation Neutralisation tests Agglutination tests ELISA tests Complement Fixation Tests (CF). Precipitation tests.

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Precipitation tests

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  1. Precipitation tests Agar immunodiffusion Lab 5

  2. Serological Tests • Precipitation tests • Antigen/Ab conjugation • Neutralisation tests • Agglutination tests • ELISA tests • Complement Fixation Tests (CF)

  3. Precipitation tests • One of the properties of some antibody classes is the ability to precipitate from solution when combined with multivalent antigens; such reactions can be visualized • This behavior is called precipitation

  4. Agglutination tests • Antibodies can agglutinate multivalent particulate antigens, such as red blood cells or bacteria • This behavior is called agglutination. • Serological tests based on agglutination are usually more sensitive than those based on precipitation

  5. Neutralisation tests • Usually used for viral or bacterial/toxin identification • Antibody neutralises the toxin and prevents its action (antitoxins) • Requires an indicator system e.g. lab animals, tissue culture, etc

  6. Antigen/Ab conjugation • Antigens (or immunoglobulins) can be conjugated with other molecules (radioisotopes, enzymes or fluorescent dyes) so that antigen-antibody binding can be detected at extremely low concentrations. • Examples are radioimmunoassay or enzyme-immunoassay, Fluorescent antibody tests (FAT).

  7. Guide to the use of Serological Tests Which test? Consider : • the organism • the most accurate test (sensitivity/specificity) • quantitative vs qualitative • the legal status of the test • the material (sample) submitted

  8. Precipitation Tests • Used for soluble antigen • When soluble antigen reacts with its specific antibody in solution, the antigen-antibody complex may become insoluble and precipitate • Relatively less sensitive • Examples • Ring precipitation test • Lancefield grouping • Agar gel immunodiffusion (AGID) • Optimal proportions of antigen and antibody causes precipitation • Excess antibody or antigen → no precipitation

  9. Ring precipitation test

  10. Lancefield grouping

  11. Agar Gel Immunodiffusion • Agar gel in plates or on microscope slides • Make wells in agar for both antigen and antibody • Two reactants diffuse into agar and form immunoprecipitates where optimal proportions occur

  12. Reaction of identity

  13. Reaction of partial identity

  14. Reaction of non-identity

  15. Radial Immunodiffusion Antigen Antiserum Decreasing Antigen Concentration

  16. Log Ag conc. Diameter of the precipitation ring • Prepare a standard curve • Allows exact quantification of antigen

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