Applications of Immune Responses

1. Applications of Immune Responses • Chapter 17

2. Smallpox • Smallpox virus (or plague bacteria [Yersina pestis]) has killed more people than any other infectious disease • In the first half of the 1900s, smallpox was killing 4 million people worldwide each year • In 1958, the Soviet Union proposed the global eradication of smallpox by using a concerted vaccination program • Smallpox infects only humans, thus it could be eradicated • The program was started in the late 1960s • The last case of smallpox was in 1977

3. Representation of the Effects of Smallpox Vaccination

4. 17.1 Principles of Immunizations • Vaccines safely elicit an adaptive (T cell and B cell) immune response to pathogenic microbes • In the process, they stimulate: • High-affinity antibodies • Class switching of antibodies (e.g., IgG, IgA) • Memory T cells and B cells • There are two types of vaccines • Inactivated (all bacteria and some viruses) • Attenuated-live (some viruses)

5. 17.1 Principles of Immunizations

6. 17.1 Principles of Immunizations

7. 17.2 Vaccine and Immunization Procedures • Attenuation • Use of a similar virus that is non-pathogenic • Vaccinia virus for smallpox • Relies upon cross-reactive immunity • Serial passage of pathogenic virus in cell culture or embyronated eggs • Since cells and eggs have no immune system, mutant viruses arise that lose virulence • These viruses often retain their antigenic determinants and thus elicit strong immunity

8. 17.2 Vaccine and Immunization Procedures • Inactivation • Formalin (37% formaldehyde) • Cross-links proteins and nucleic acids • Used for toxoid (inactivated toxin) vaccines, such as tetanus • β-propiolactone (BPL) • Nucleic acid mutagen • Breaks down rapidly • After 24 hours, virtually none exists in a vaccine preparation

9. 17.2 Vaccine and Immunization Procedures • Inactivated vaccines • Whole-agent: entire microbe is in the vaccine (inactivated poliovirus) • Toxoid: No cells, just their toxin(s) (tetanus) • Protein subunit vaccine: Only antigenic subunits (acellular pertussis, hepatitis B) • Polysaccharide conjugate vaccines • By conjugating (covalently-linking) polysaccharide antigens to proteins, the antigen becomes T-dependent • Haemophilus influenzae type b (Hib) and Streptococcus pneumonia • Requires an adjuvant (e.g aluminum hydroxide) to stimulate the innate immune response

10. 17.2 Vaccine and Immunization Procedures Advantages/Disadvantages of Attenuation

11. 17.2 Vaccine and Immunization Procedures Advantages/Disadvantages of Inactivation

12. 17.2 Vaccine and Immunization Procedures • The importance of routine immunization in children • Prior to the use of routine immunization, thousands of children died or were disabled by infectious diseases in the U. S. • Globally, measles still kills 700,000 people, mostly children, per year • By immunizing, the incidence of the disease, and consequently the microbe, decrease substantially • For each infectious disease, a target vaccine coverage rate is needed to reduce the incidence of disease to nearly zero • For measles, this rate is 95%

13. 17.2 Vaccine and Immunization Procedures • Vaccine side effects • Risk • The risk of vaccination is not zero • But the risk of not vaccinating is far greater • Those who do not immunize their children take advantage of those who do assume the risks • Vaccines and autism spectrum disorders • Large-scale population studies have shown that the incidence of autism spectrum disorders in vaccinated and unvaccinated populations is virtually the same

14. 17.2 Vaccine and Immunization Procedures • Japan’s experience with pertussis (whooping cough) • 1972: Mandatory vaccination at 3 months reduces the incidence of pertussis to fewer than 300 cases per year • 1973-74: Two children die shortly after vaccination • 1974: Politicians change the first vaccination age to 2 years (instead of 3 months) • 1979: Japan reports more than 13,000 cases of pertussis with 41 deaths. Some surviving have permanent neurological damage (which is what pertussis toxins do) • 1980: Japan returns to their previous vaccine schedule and within a few years the incidence of pertussis returns to 1972 levels • Vaccines are often victims of their own success

15. 17.3 Principles of Immunologic Testing • Antibodies are generated in response to infection • The presence of antibodies in the blood (serum) to a pathogen are highly suggestive of infection • Detection of IgM indicates recent infection • Detection of IgG indicates recent or distant infection • The study of blood antibodies is serology

16. 17.3 Principles of Immunologic Testing • Blood collection • Collect blood without anticoagulants • Allow to stand at room temp 30 min for clot formation, then at 4° C for 1 hour for contraction • Centrifuge the blood to separate clot from serum • Aspirate the serum into a new tube • Dilute for testing (usually 1:20 for IgM or 1:100 for IgG testing)

17. 17.3 Principles of Immunologic Testing • Serological tests • Agglutination (e.g. influenza typing) • Precipitation • Immunofluorescence • Enzyme-linked immunosorbant assay (ELISA) • Western blot

18. 17.5 Using Labeled Antibodies to Detect Antigen-Antibody Interactions • ELISA • Antigen: Coat known protein antigen to a solid-surface • Polyvinyl chloride (PVC) is commonly used because it has a high affinity for proteins • Serum sample: Add patient’s serum and incubate 1 hour • If antibodies to the antigen are present, they will bind to the antigen coated on the plate • Detection antibody: Wash with saline, then add an enzyme-conjugated anti-human IgG antibody • If the patient has antibodies, they will be bound by the detection antibody • Substrate: Wash with saline, then add substrate that turns color in the presence of the enzyme