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