Chapter 17:

1. Chapter 17: Immunization and Immune Testing

2. Immunology • Based on adaptive (specific) immunity • Humoral or antibody mediated • B cells produce antibodies • Cellular • T cells can directly attack pathogens

3. Immunization • Two Artificial Methods of Immunity • Active immunization • administration of a vaccine • patient actively produces antibodies • Passive immunization • individual acquires immunity through direct transfer of antibodies

4. Brief History of Immunization • 12th century Chinese and variolation • Spread to England and America • 1796 – Edward Jenner discovered process of vaccination • Smallpox • 1879 – Louis Pasteur developed vaccine • Avirulence of Pasteurella multocida • Anthrax and rabies vaccines • Discovery that vaccines protected through the action of antibodies lead to practice of transferring antibodies directly

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6. Vaccination Development Issues • Socioeconomic and political problems prevent nations from receiving vaccines • Effective vaccines unavailable for some pathogens • Vaccine-associated risks discourage investment in developing new vaccines

7. Active Immunization • Vaccine types • Attenuated (live) vaccines • Contain active pathogens with reduced virulence • stimulate a strong immune response due to the large number of antigen molecules • Can result in mild infections but no serious disease

8. Inactivated (killed) vaccines • Whole agent vaccines –deactivated but whole microbes • Subunit vaccines –antigenic fragments of microbes • Both types are safer than live vaccines because they cannot replicate or mutate to a virulent form • Antigenically weak so contain adjuvants

9. Toxoid vaccines • Modified toxins used to stimulate immunity • Stimulate antibody-mediated immunity • Require multiple doses because they possess few antigenic determinants

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12. Problems with existing active immunizations: • Mild toxicity most common • Risk of anaphylactic shock • Residual virulence from attenuated viruses • Allegations that certain vaccines cause or trigger autism or other diseases • Research has not substantiated these allegations

13. Passive Immunization (Immunotherapy) • Antiserum • Contains preformed antibodies • Provides immediate protection • Limitations: • Contains antibodies against many antigens • Can trigger serum sickness (allergic reaction) • May be contaminated with viral pathogens • Antibodies are degraded relatively quickly

14. Many limitations overcome through development of hybridomas

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16. Immune Testing • Serology • study of antigen-antibody interactions in blood serum • Diagnostic uses • Use known antibodies to detect antigens associated with an infectious agent • Use antigens to detect specific antibodies in a patient’s blood to determine exposure to a specific pathogen

17. Tests are chosen based on: • suspected diagnosis • cost to perform the test • speed with which results can be obtained

18. Precipitation Tests • Antigens and antibodies mixed • Form large macromolecular complexes called precipitates • Correct proportions are vital to create precipitation

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20. Agglutination Tests • Clumping due to cross-linking of antibodies with antigens • Hemagglutination used to determine blood type

21. Labeled Antibody Tests • Antibody molecules are linked to some molecular “label” that enables them to be easily detected • Radioactive or florescent • Used to detect either antigens or antibodies

22. ELISA (enzyme-linked immunosorbent assay) • Uses enzyme as label • Reaction of the enzyme with its substrate produces a colored product • Most commonly used to detect antibodies in serum

23. Antibody sandwich ELISA • Modification ELISA technique • Commonly used to detect antigen • Antigen being tested for is “sandwiched” between two antibody molecules

24. Advantages of the ELISA • Can detect either antibody or antigen • Can quantify amounts of antigen or antibody • Easy to perform, inexpensive, and can test many samples quickly