Immunization and Applications of the Immune Response 18

Immunization CH18

Vaccine Types

Vaccines are biological preparations that provide acquired immunity to specific infectious diseases. They can be classified based on their composition and method of preparation.

• Attenuated (Modified Live) Vaccines:

  • Use pathogens with reduced virulence.

  • Process of reducing virulence is called attenuation.

  • Can result in mild infections but usually do not cause disease in healthy individuals.

  • Active microbes stimulate a strong immune response.

  • Can provide contact immunity (immunity passed to others).

  • Not recommended for immunocompromised individuals.

• Inactivated (Killed) Vaccines:

  • Whole agent vaccines: Contain deactivated but whole microbes.

  • Subunit vaccines: Contain antigenic fragments of microbes.

  • Often require multiple doses to achieve full immunity.

  • May include adjuvants to increase effectiveness (adjuvants are substances that enhance the body's immune response to an antigen).

  • Cannot replicate, so they are safer but may be less effective than live vaccines.

• Toxoid Vaccines:

  • Contain inactivated toxins (toxoids) produced by pathogens.

  • Stimulate antibody-mediated immunity against the toxin rather than the microbe itself.

  • Require multiple doses and boosters.

• Combination Vaccines:

  • Combine antigens from several pathogens into one vaccine (e.g., DTaP).

• Recombinant Vaccines:

  • Use genetically engineered microbes or microbial antigens.

  • Can include vaccines that use recombinant DNA technology.

Applications of the Immune Response

Serology

Serology is the study and diagnostic identification of antibodies or antigens in blood serum. It is widely used to detect exposure to pathogens and to diagnose diseases.

• Antibody Titer: The concentration of antibodies in a sample. Determined by serially diluting serum and testing for the presence of antibodies using agglutination or other assays.

• Agglutination Tests:

  • Based on the clumping of antigen-antibody complexes.

  • Can be used to determine blood type and to detect the presence of specific antigens or antibodies.

  • Types:

    • Direct Agglutination: Antibodies react with antigens on the surface of cells (e.g., red blood cells).

    • Indirect (Passive) Agglutination: Antibodies or antigens are attached to particles (e.g., latex beads) to enhance visibility of agglutination.

• Precipitation Tests:

  • Involve the formation of insoluble antigen-antibody complexes.

  • Used to detect the presence of specific antibodies or antigens in a sample.

• Neutralization Tests:

  • Assess the ability of antibodies to neutralize the biological activity of pathogens or toxins.

  • Commonly used for viruses (e.g., viral neutralization test, viral hemagglutination inhibition test).

• Complement Fixation Test:

  • Detects the presence of specific antibodies by measuring the consumption of complement proteins during antigen-antibody reactions.

• ELISA (Enzyme-Linked Immunosorbent Assay):

  • Highly sensitive and specific immunoassay.

  • Can detect either antigen or antibody.

  • Enzyme-substrate reaction produces a colored product, indicating a positive result.

  • Commonly used for diagnostic purposes (e.g., HIV testing, pregnancy tests).

  • Advantages:

    • Can quantify amounts of antigen or antibody.

    • Easy to perform and can test many samples quickly.

    • Relatively inexpensive and sensitive.

    • Plates coated with antigen can be stored for later testing.

• Monoclonal Antibodies:

  • Produced using hybridoma technology (fusion of antibody-producing B cells with myeloma cells).

  • Highly specific for a single epitope.

  • Used in diagnostics and therapeutics.

Recent Developments in Immune Testing

• Rapid, easy-to-read ELISAs: Provide quick results for the presence of antigens or antibodies.

• Immunochromatographic Assays:

  • Antigen solution flows through a porous strip.

  • Visible line forms where antigen-antibody immune complexes accumulate.

  • Used in pregnancy tests and for rapid identification of some infections.

Table: Comparison of Vaccine Types

Vaccine Type	Composition	Advantages	Disadvantages
Attenuated (Live)	Weakened live microbes	Strong, long-lasting immunity; may provide contact immunity	Risk for immunocompromised; possible mild infection
Inactivated (Killed)	Dead microbes or subunits	Safe; cannot cause disease	Weaker immunity; requires boosters
Toxoid	Inactivated toxins	Protects against toxin-mediated diseases	Requires multiple doses
Recombinant	Genetically engineered antigens	Safe; targeted immunity	May be less immunogenic

Key Terms

• Adjuvant: Substance added to vaccines to enhance the immune response.

• Antigen: Any substance that can induce an immune response.

• Antibody: Protein produced by B cells that binds specifically to an antigen.

• Serum: The liquid portion of blood after clotting, containing antibodies.

• Hybridoma: Cell produced by fusing a B cell with a myeloma cell, used to produce monoclonal antibodies.

Example: ELISA in Disease Diagnosis

ELISA is commonly used to detect HIV antibodies in patient serum. A positive result indicates exposure to the virus and the presence of an immune response.

Additional info: Expanded explanations and definitions were added for clarity and completeness.