View
220
Download
1
Embed Size (px)
Citation preview
Applications of Immune Responses
Chapter 17
SmallpoxSmallpox 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
Representation of the Effects of Smallpox Vaccination
Representation of the Effects of Smallpox Vaccination
17.1 Principles of ImmunizationsVaccines 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)
17.1 Principles of Immunizations17.1 Principles of Immunizations
17.1 Principles of Immunizations17.1 Principles of Immunizations
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
17.2 Vaccine and Immunization Procedures
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
17.2 Vaccine and Immunization Procedures
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 vaccinesBy 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
17.2 Vaccine and Immunization Procedures
17.2 Vaccine and Immunization Procedures
Advantages Disadvantages
Stronger antibody response
More expensive
Requires fewer boostersPerishable (live viruses);
requires refrigeration
Longer memoryPathogenic revertants
(rare)
Stimulates MHC I processing (cytotoxic T
cells)
Possible contamination with other viruses
More closely resembles natural infection
Advantages/Disadvantages of Attenuation
17.2 Vaccine and Immunization Procedures
17.2 Vaccine and Immunization Procedures
Advantages Disadvantages
Less ExpensiveWeaker antibody
response
Stable (room temp storage)
Requires mre boosters
No chance of infection Shorter memory
Contaminating viruses will also be inactivated
Does not stimulate MHC I processing (no Tc cells)
Does not resemble natural infection
Advantages/Disadvantages of Inactivation
17.2 Vaccine and Immunization Procedures
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%
17.2 Vaccine and Immunization Procedures
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
17.2 Vaccine and Immunization Procedures
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
17.2 Vaccine and Immunization Procedures
17.2 Vaccine and Immunization Procedures
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
17.3 Principles of Immunologic Testing
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)
17.3 Principles of Immunologic Testing
17.3 Principles of Immunologic Testing
Serological tests
Agglutination (e.g. influenza typing)
Precipitation
Immunofluorescence
Enzyme-linked immunosorbant assay (ELISA)
Western blot
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
17.5 Using Labeled Antibodies to Detect Antigen-Antibody
Interactions
17.5 Using Labeled Antibodies to Detect Antigen-Antibody
Interactions