Applications of Immunology

Applications of Immunology

• Vaccinations

  • Used to immunize individuals against diseases.

• Types of Vaccines:

  • Live attenuated vaccines:
  • Pathogen is weakened through chemical treatments or culturing in unsuitable environments.
  • These vaccines multiply in the host body and provoke an immune response.
  • Inactivated vaccines:
  • Pathogens are killed by heat or chemicals.
  • Vaccine components still promote an immune response.
  • Toxoids:
  • Inactivated toxins used to immunize against specific toxins (e.g., tetanus and diphtheria toxoids).
  • Acellular vaccines:
  • Use only fragments of the pathogen to promote an immune response, minimizing potential adverse reactions.
  • Subunit vaccines:
  • Produced by recombinant DNA technology (e.g., Hepatitis B, Recombivax®) by cloning viral proteins into yeast cells to use as vaccines.

Immunization Schedule

• CDC recommendations for childhood and adult vaccinations:
  • Vaccination schedule varies by age from birth to ≥65 years old, with several recommended vaccines:
  • Children: Hepatitis B, DTaP (diphtheria, tetanus, pertussis), MMR (measles, mumps, rubella), IPV (inactivated polio), etc.
  • Adults: Boosters such as Tdap (tetanus, diphtheria, pertussis) and Td (tetanus and diphtheria) recommended every 10 years.
  • There are catch-up immunization schedules for those who miss vaccinations.

Diagnostic Applications

• Serological Testing:

  • Serum from patients is tested for antibodies/antigens to determine exposure, ongoing infection, or vaccination against specific antigens.

• Immunodiagnostics Techniques:

  • Various tests rely on the binding of antibodies to antigens, including:
    • Agglutination
    • Hemagglutination
    • Precipitation
    • Fluorescent antibody methods
    • ELISA assays (Enzyme Linked Immunosorbent Assay)
    • Complement fixation tests

Precipitation Tests

• Patient antibodies bind to specific antigens in solution, leading to visible precipitation, indicating a positive reaction.
• Primarily qualitative (yes/no) assessment.

Agglutination Tests

• Agglutination occurs when viruses agglutinate RBCs if antibodies against the virus are absent; it will not occur if antibodies are present.
• Can also be quantitative to determine antibody titers through serial dilutions of patient serum.

Labeled Antibodies

• Commercially available antibodies labeled with radioactive, fluorescent, or enzyme markers are utilized to identify specific antigens from patient samples.
• UV microscopy is used for viewing the fluorescent antibodies.

Complement Fixation Test

• A classic test for diagnosing diseases (e.g., syphilis).
• Performed in vitro by adding patient serum to an antigen, and complement fixation is detected using sheep erythrocytes.

ELISA (Enzyme Linked Immunosorbent Assay)

• Utilizes plastic microtiter plates for detecting either antibodies (indirect ELISA) or antigens (direct ELISA).
• Steps for Indirect ELISA:
  1. Antigen is attached to the well in a plate.
  2. Blocking protein (gelatin) is added to prevent uncoated surfaces from binding.
  3. Patient serum is added, allowing antibodies to bind to the antigen.
  4. Enzyme-linked anti-antibody is added to bind to the bound antibody.
  5. A substrate for the enzyme is added, leading to a color change indicating a reaction.

Monoclonal Antibodies

• Key for many diagnostic tests; made by fusing sensitized mouse B-cells with myeloma cells in vitro to form hybridomas, producing specific antibodies continuously in culture.

Western Blotting

• Technique used to identify antigens in patient samples (e.g., HIV testing).
• Involves separating proteins via electrophoresis, transferring them to a nitrocellulose membrane, and probing with a specific solution to check for the presence of HIV antigens.

Immunochromatographic Tests

• Uses dipstick techniques where antibodies are linked to colloidal metals; visible color change indicates the presence of specific antigens (e.g., Strep A test).

Summary Table of Immunological Tests

• Test Types and Uses:
  • Immunodiffusion, agglutination, viral neutralization, complement fixation, ELISA, and Western blot, each serving specific diagnostic purposes related to various infections and conditions.