CSIM 1.28 Principles of Immunisation

Question 1

When is MMR given and why?

Answer 1

1st birthday because passive immunity from mother covers this for first year

Question 2

What can be given for passive immunity?

Answer 2

• T cells

* Monoclonal antibodies (An antibody made from a single immortalised B-cell)

Question 3

What are the types of vaccine? How many doses is usually needed for each?

Explain the difference in number of doses

Answer 3

Live attenuated (one dose)
• Weakened
• Must be able to replicate to be effective
• Do not give if pregnant or immunocompromised

Inactivated (3 doses)
• Can be bits of virus or bacteria
• Can be whole-cell
• Cannot replicate

there is no inflammation induced by the inactivated, so the immune response is mostly humoral and so requires more doses

Question 4

What are the common live attenuated vaccines?

Answer 4

Viral
  •  MMR
  •  Vaccinia
  •  Varicella
  •  Yellow fever
  •  Rotavirus
Bacterial 
  •  BCG

Question 5

What are the types of inactivated vaccines?

Answer 5

WHOLE
  •  Polio
  •  Hepatitis A
  •  Flu
  •  Rabies

FRACTIONAL
Subunit
• Hepatitis B

Toxoid
• Diphtheria
• Tetanus

Pure Polysaccharide
• Pneumococcal
• Meningococcal ACWY
• Salmonella

Conjugate Polysaccharide
• HiB
• Pneumococcal 7 and 13
• Meningococcal B and C

Protein

NB: Toxoid = bacterial toxin whose toxicity is inactivated but immunogenicity preserved

Question 6

What are the types of antigen?

Answer 6

• Thymus-dependent antigen

* Thymus-independent antigen

Question 7

Describe thymus-independent antigens:
  •  Interaction with MHC
  •  Use of T cells
  •  Type of molecule/antigen
  •  Antibodies type produced
  •  Class switching

Answer 7

• Not MHC-dependent
  
  • Antibody response occurs without mature T cells help
  • Carbohydrate antigens
  • Antibodies are IgM and IgG2
  • No class switching or memory

Question 8

What do thymus-independent antigens activate and how?

Answer 8

B cells
• 1st signal is delivered by a direct antigen-receptor interaction
• 2nd signal is generated through toll-like receptors (TI-type 1) or through multiple cross-linking of BCRs (TI-type 2)

Question 9

What are the types of thymus-independent antigens? Describe the main features of these

Answer 9

TI-type 1
• Works by directly binding BCR receptors and activating toll-like receptors
• Activates many B cells when at a high concentration, such that all the activated B cells are not antigen specific - polyclonal (IMG 71)
• At low concentrations the B cell activated is monoclonal and specific (IMG 72)

TI-type 2
• Activate B cells that appear late in development (ontogeny)
• Work by cross-linking BCR receptors

Question 10

Which immunoglobulin type is formed by TI-type 2 antigens?

Answer 10

IgM

Question 11

Describe conjugated vaccines and why they are superior to pure polysaccharide vaccines

Answer 11

Pure polysaccharide vaccines are not immunogenic in children under 2. The antibody produced no affinity maturation and there is often hypo-responsiveness which results from anergy

The polysaccharide antigen can be conjugated to an unrelated protein, allowing a thymus-dependent response to occur rather than a thymus-independent response which is seen with pure polysaccharide antigens

This is because the protein can be processed by MHC, but with the polysaccharide antigen still attached

Question 12

What is an adjuvant?

Give a common example.

Answer 12

A substance that is added to a vaccine to increase the body’s immune response to the vaccine
• Provokes a local inflammatory response

Aluminium hydroxide

Question 13

Describe the HPV vaccine

Answer 13

A vaccinia virus is used, with recombinant genes including an HPV 16 L1 gene inserted using plasmids

Question 14

Why is an HIV vaccine difficult to produce?

Answer 14

HIV has a high mutation rate and can easily reverse attenuation, and also means that one vaccine will not protect against all mutations of HIV