Download Chapter 17: Immunization and Immune Testing

Chapter 17:
Immunization and Immune Testing
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Immunology
• Based on adaptive (specific) immunity
– Humoral or antibody mediated
– B cells produce antibodies
– Cellular
– T cells can directly attack pathogens
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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
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• 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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• 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
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• 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
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– 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
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– 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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• 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
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• 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
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Many limitations overcome
through development of
hybridomas
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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
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• Tests are chosen based on:
– suspected diagnosis
– cost to perform the test
– speed with which results can be obtained
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• Precipitation Tests
– Antigens and antibodies mixed
– Form large macromolecular complexes called precipitates
– Correct proportions are vital to create precipitation
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• Agglutination Tests
– Clumping due to cross-linking of antibodies
with antigens
– Hemagglutination used to determine blood type
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• 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
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• 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
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• Antibody sandwich ELISA
– Modification ELISA technique
– Commonly used to detect antigen
– Antigen being tested for is “sandwiched”
between two antibody molecules
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• 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
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