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Immunology vs. Serology

Immunology vs. Serology. Immunology Study of immune system Serology Detecting/measuring elements of humoral immune system (I.e., antibodies) Help diagnose infectious disease & immunologic disorders Determine immune status. When to Use Serology. Unable to culture infectious agent

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Immunology vs. Serology

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  1. Immunology vs. Serology • Immunology • Study of immune system • Serology • Detecting/measuring elements of humoral immune system (I.e., antibodies) • Help diagnose infectious disease & immunologic disorders • Determine immune status

  2. When to Use Serology • Unable to culture infectious agent • Confirmation of etiologic agent ID • Diagnosis of immunologically-related disorders (ex. autoimmune disorders) • Determine immune status(ex. immunity to Rubella, Hepatitis B)

  3. Antigens • Molecular weight • Foreignness • Complexity • Structural stability • Degradability

  4. Antibodies • IgM • IgG • IgA • IgD • IgE

  5. Primary Antibody ResponseIn vivo • First antibody formed? IgM • IgM & IgG

  6. Secondary Antibody ResponseIn vivo • IgG predominates (IgM also formed) • Antibody concentration compared to 1°? Greater in secondary response

  7. Antibody – Antigen InteractionsIn vitro • Two steps in the detection of in vitro antigen/antibody reactions • Sensitization(initial attraction) • Lattice formation(committed, long-lasting relationship)

  8. Affinity = Dissociation Sensitization • Due to affinity • Initial attraction • Reversible

  9. Lattice Formation • Ab >1 binding site • Ab binds to multiple Ag sites • Avidity (sum of all attractive forces) • Stronger bond than sensitization • “lock a door”

  10. Test Condition Influenceson Lattice Formation • Ratio of available Ab and Ag Prozone Postzone

  11. Test Condition Influenceson Lattice Formation • Prozone • No visible reaction • If patient antibody is what is being tested for, then false _______ result negative

  12. Test Condition Influenceson Lattice Formation • Postzone • No visible reaction • If patient antigen is what is being tested for, then false ________ result negative

  13. Test Condition Influenceson Lattice Formation • pH – usually 7.0 • Temperature of Incubation • Warm reactive, 37°C = • Cold reactive, 4-22°C = IgG IgM • Length of reaction • Immunoglobulin class • Strength of Ab-Ag reaction

  14. Test Condition Influenceson Lattice Formation • Which antibody is the best agglutinator? IgM 750x better agglutinator than IgG

  15. Test Condition Influenceson Lattice Formation • Ionic strength Ab- Ab- Ag- Ag- Ab- Ab- Ab- Ag- Ag- Ag- Ab- Ab- Ag- Ab- Like charges repel each other

  16. Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Test Condition Influenceson Lattice Formation • Buffer solutions supply Na+ and Cl- Ag- Ag- Ab- Ab- Ab- Ab- Ag- Ag- Ag- Ag- Ab- Ab- Sodium ions neutralize negative charges Sensitization & lattice formation can occur

  17. Test Condition Influenceson Lattice Formation • Steric Hindrance • Physical or mechanical blocks • Different antibodies directed at separate antigenic determinants on one antigen…may get in the way of each other • IgG Ab block sites for IgM Ab • Lack of space around Ag due to complement, etc.

  18. Specificity vs. Sensitivity • A test with a high degree of _______ will have a low number of false positives. • A test with a high degree of _______ will have a low number of false negatives. • The difference between specificity & sensitivity is…

  19. Sensitivity & Specificity • Sensitive = detect small amount of antigen or antibody • If it is there, I’ll find it • Specific = will only be positive or react with particular antigen or antibody • If the test is positive, you can be sure it is a true positive

  20. Sensitivity & Specificity specificity • A test with a high degree of __________ will have a low number of false positives. sensitivity • A test with a high degree of _________ will have a low number of false negatives.

  21. Sensitivity & Specificity • Antibodies made in response to an exposure to the bacteria Brucella sp. (causes a person to develop fevers and become lethargic) also react with the bacteria Francisella tularensis. • The Brucella antibody ___________ with the Francisella organism. cross-reacts is not • The Brucella antibody a specific antibody.

  22. Titer • Relative concentration of specific antibody or antigen • Reciprocal of the highest dilution in which a positive reaction occurs • When testing acute and convalescent sera, a 4-fold rise in titer is considered evidence of a recent infection

  23. Evidence of Recent Infection • See example on page 26 of your notes • Acute titer = 1:20 (last dilution tested w/ + rxn) • Convalescent titer = 1:80 • This exhibits a 4-fold rise in titer or a 2-tube difference (using serial 2-fold dilutions) • The acute and convalescent titers should be tested at same time • Not practical • Often a high single titer determines recent infection

  24. Heat Inactivate Serum • Removes complement or other substances in serum that are known to interfere with certain serologic tests • Procedure • 56°C, for 30 minutes • >4 hrs since last inactivation • Re-inactivate 56°C, for 10 minutes

  25. Summary • Immunology versus Serology • Antigens & Antibodies • Antibody Response • Antigen-Antibody Interactions • Other key terms

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