Defense against bacteria Flashcards
What are the properties of a good vaccine?
- Stimulates an effective immune response
- Safe and doesn’t cause adverse reactions
- Inexpensive
- Stable
- Easy to administer
- Simple for manufacturer and regulatory authorities to control
How is vaccine efficacy determined?
- Reducation of incidence of disease among people who received a vaccine in comparison to incidence in non vaccinated people
- Determined during phase 3 trial
- Efficacy is 1-(attack rate in vaccinated/attack rate in placebo)
What is herd immunity?
- Form of immunity that occurs when vaccination of a significant portion of population provides a measure of protection for individuals who have not yet developed immunity
- Stopping transmission to population because organism is not circulating
What are the parts of a vaccine?
- Antigen
- Adjuvant
- enhance and modulate response - Excipients
- buffer, salts, sugars and proteins to maintain vaccine pH, osmolarity and stability
- Also contains preservatives
What are the types of vaccine antigens?
- Complex, multiple antigens
- Live attenuated
- Killed whole - Individual or number of well defined antigens
- Purified component vaccines
- Toxoids
- Polysaccharide conjugates
Why are polysaccharides poorly immunogenic?
- Doesn’t lead to good memory
- Predominantly IgM
- No affinity maturation
What are the benefits of this vaccine?
- Simple to produce
- Relatively pure
- Safe
- High protective efficacy
What is another successive vaccine strategy?
- Pertussis whole cell vaccine
Why was it discontinued?
- Anaphylaxis
- Prolonged crying seizures
- Encephalopathy
- Acellular vaccine now used
What are conjugate vaccines?
- Carbohydrate chemically linked to immunogenic protein
- T cell recognition of protein carriers enhances b cell activation and promotes efficient antibody response to polysaccharide capsule
What are the benefits of conjugate vaccines?
- Effective for humoral (antigen) responses
- Highly purified components
- Safe
- Give specific characteristics which can be used in quality control
What are the problems with conjugate vaccines?
- Sophisticated technology so more expensive
- Can’t always be used e.g meningococcal polysaccharide similar to self
What are some licensed conjugate vaccine:
- Hib
- Pneumococcal conjugate
- MenC conjugates
What are live attenuated vaccine?
- Prepared form live microorganism or functional viruses
- Whole disease producing ability has been weakened but whose immunogenic properties have been not
What live attenuated vaccine are currently used?
- BCG gives some protection in children but ineffective against adult pulmonary disease
- Attenuated mycobacterium bovis - Very effective ones being developed for enteric pathogens
- E.g typhoid vaccine - Cholera
- High risk areas
What are adjuvants?
- Delivery symptoms
- Mineral salts
- Surface active agents - Immune potentiators
- Toxins and lipids
- Nucleic acids
- Peptidoglycan
Should we vaccinate immunocompromised people?
- Better heard immunity
- Protect in close contact
- Decision depends on nature of immunodeficiency and vaccine itself
How do bacteria resist complement
- Thick cell walls (TB)
- Capsule (n.meningitidis)
Diseases for which vaccines can be successfully?
Meningococcal
- Outer membrane vesicle vaccine
- Contain all antigens associated with outer membrane
- Only good protection against homologous vaccine
Pneumococcal
What are the components of the DTP vaccine?
diphtheria, tetanus, pertussis (whooping cough)
- subunit vaccines
- antibodies neutralise toxins and block adhesion
How do bacteria resist phagocytosis?
- Polysaccharide capsule (n.meningitidis)
- Debilitate phagocytes (yersinia pestis)
- Hide inside other cells (chlamydia)
How do bacteria inhibit intracellular killing
- Escape from phagosome (listeria monocytogenes)
- Block phagosome maturation (TB)
How do bacteria resist antibodies?
- IgA protease (strep.pneum)
- antigenic variation (n.gonnorhea)
