Transcript chapter17

Applications of Immune
Responses
Chapter 17
Smallpox virus (or plague
bacteria
Smallpox
[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
Representation of the Effects of
Smallpox Vaccination
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)
17.1 Principles of Immunizations
17.1 Principles of Immunizations
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
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
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
17.2 Vaccine and Immunization
Procedures
Advantages/Disadvantages of Attenuation
Advantages
Disadvantages
Stronger antibody response
More expensive
Requires fewer boosters
Perishable (live viruses);
requires refrigeration
Longer memory
Pathogenic revertants (rare)
Stimulates MHC I processing
(cytotoxic T cells)
Possible contamination with
other viruses
More closely resembles
natural infection
17.2 Vaccine and Immunization
Procedures
Advantages/Disadvantages of Inactivation
Advantages
Disadvantages
Less Expensive
Weaker 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
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
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
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
17.3 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
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
Serological tests
Agglutination (e.g. influenza typing)
Precipitation
Immunofluorescence
Enzyme-linked immunosorbant assay
(ELISA)
Western blot
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 enzymeconjugated 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