11 - Pregnancy and Vaccines

Question 1

What stops the immune system from attacking non-self foetus in pregnancy?

Answer 1

1. Partial and selective suppression of immune functions
2. In some cases, women have too high levels of IgA in vagina meaning that sperm are killed before they can fertilise eggs
   a) To bypass this, taking a sample of sperm and injecting it via tube by inserting it past the cervix to ensure sperm skip immune response
3. Embryo causes inflammation of uterine wall, especially at point of implantation
   a) Immune system of mother is modified by certain hormones released
   b) Implanting cells of trophoblasts do not display MHC “self” protein markers to evade immune system
4. Non-specific defences:
   a) WBC count goes up, especially the neutrophils which are first on scene in inflammation
   b) Local concentrations of placental corticosteroids suppress the activity of phagocytes

Question 2

Describe the non-specific defence suppressed during pregnancy:

Answer 2

1. WBC count goes up, especially the neutrophils which are first on scene in inflammation
2. Local concentrations of placental corticosteroids suppress the activity of phagocytes
3. Trophoblast cells secrete cytokines that suppress IL-2, tumour necrosis factor, interferon, NK cell activity
   a) Natural killer cells are capable of attacking foreign cells without MHC markers (foetus vulnerable) so these must be suppressed
   b) Tumour necrosis factor also needs to be suppressed

Question 3

Describe the specific defence suppressed during pregnancy:

Answer 3

1. T-cell activity is potentially the most dangerous to blastocyst/embryo
   a) T-cells are designed to recognise cell that are non-self and destroy them
   b) However they need to observe MHC, trophoblasts don’t display MHC so evade T cell activity
2. Pregnancy induces Th2 shift
   a) Th1 aborts foetus whereas Th2 protects foetus
   b) This change is likely due to hormonal control of high oestrogen and progesterone
   c) Consequences to this mean mother is more vulnerable to virus infections which could be life-threatening because there is a shift away from Th1 response

Question 4

What is a vaccine?

Answer 4

1. A preparation of a disease-causing agent or its products to induce active immunity
   a) In order to prevent an infection, you need to trigger the adaptive immune response prior to infection, vaccines fool the immune system into thinking it has already seen the pathogen

Question 5

How do vaccines work?

Answer 5

1. They induce a “primed” state in the vaccinated subject so that the following exposure to a pathogen, a rapid secondary immune response is generated
2. Success depends on the generation of memory T and B cells and the presence in the serum of neutralising antibody

Question 6

What is the importance of vaccines?

Answer 6

1. Herd immunity: protection conferred to unvaccinated individuals in a population produced by vaccination of others and reduction in the natural reservoir for infection
   a) Herd immunity effect is seen only at relatively high levels of vaccination within a population

Question 7

What are the requirements for a successful vaccine?

Answer 7

1. Cannot cause illness or death
2. Must protect against illness resulting from exposure to live pathogen
3. Protection against illness must last for several years
4. Neutralising antibody is essential to prevent infection of cells that cannot be replaced
5. Low cost per dose

Question 8

What is passive immunisation vaccination?

Answer 8

1. The injection of purified antibody, antibody-containing serum, or immune cells to provide rapid temporary protection or treatment of a person
   a) Newborns receive natural passive immunity from maternal immunoglobulin that crosses the placenta or is present in the mother’s milk
2. Passive immunisation may be used:
   a) To prevent disease after a known exposure (e.g. needlestick injury with blood that is contaminated with HBV)
   b) To ameliorate the symptoms of an ongoing disease
   c) To protect immunodeficient individuals
   d) To block the action of bacterial toxins or venoms and prevent the diseases they cause

Question 9

What is active immunisation vaccination?

Answer 9

1. Occurs when an immune response is stimulated because of challenge with an immunogen, such as exposure to an infectious agent (natural immunisation) or through exposure to microbes or their antigens in vaccines
   a) On subsequent challenge with the virulent agent, a secondary immune response is activated that is faster and most effective at protecting the individual, or antibody is present to block the spread or virulence of the agent

Question 10

What are live attenuated vaccines?

Answer 10

1. Virus is taken and grown in culture
2. Virus is used to infect monkey cells
3. Virus acquires mutations that allow it to grow well in monkey cells
4. The virus no longer grows well in human cells (it is attenuated) and can be used as a vaccine
5. Attenuation can be achieved more rapidly and reliably with recombinant DNA techniques

Question 11

What are the advantages and disadvantages of live attenuated vaccines?

Answer 11

1. Adv:
   a) They activate all phases of immune system
   b) They raise immune response to all protective antigens
   c) They offer more durable immunity and are more cross-reactive
   d) They cost less to produce because there are less steps involved
   e) Administration is usually easy
   f) These vaccines are easily transported in the field
   g) They can lead to elimination by the wild-type virus from the community
2. Disadvantages:
   a) Mutation can occur and reverse to virulence
   b) Spread to contacts of vaccinees
   c) Live viruses are a problem in immunodeficient patients
   d) Can be less effective in tropical environments due to heat

Question 12

What are the advantages and disadvantages of killed whole organism (inactivated) vaccines?

Answer 12

1. Adv:
   a) They give sufficient humoral immunity if boosters are given
   b) There is no mutation or reversion to virulence
   c) They can be used in immunodeficient patients
   d) They sometimes perform better in the tropics
2. Disadvantages:
   a) Immunity does not last long
   b) Some vacinees do not raise immunity
   c) Boosters tend to be needed
   d) Higher cost

Question 13

What are adjuvant vaccines?

Answer 13

1. An immunological agent that modifies the effect of other agents
2. Adjuvants affect the immune response in various ways:
   a) To increase the immunogenicity of weak antigens
   b) To enhance speed and duration of immune response
   c) To stimulate and modulate humoral responses, including antibody isotype
   d) To stimulate cell-mediated immunity
   e) To improve induction of mucosal immunity
   f) Enhance immune responses in immunologically immature patients, particularly infants
   g) To decrease the dose of antigen required; reducing costs and eliminating inconvenient requirements for booster shots
3. Types of adjuvants:
   a) Inorganic salts
   b) Bacterial products
   c) TLR agonists
   d) Natural mediators (cytokines)