Overview of I&I

Question 1

Who is more vulnerable to infectious disease?

Answer 1

Elderly and children (usually)

Question 2

Major groups of pathogenic bacteria

Answer 2

Pyogenic (puss forming)
Enteric
Exotoxin producers
Facultative intracellular parasites (e.g. Shigella) - capable of living and reproducing either inside or outside of cells

Question 3

Examples of eukaryotic parasites

Answer 3

Malaria, leishmaniasis, sleeping sickness

Question 4

Describe viruses

Answer 4

Obligate intracellular parasites which can cause disease by inducing
inflammation, causing cell death, increasing the likelihood that a tumour
will develop.

Question 5

What may fungi cause?

Answer 5

thrush, athletes’ foot, ringworm.

Question 6

Describe the microbiota?

Answer 6

• Non-pathogenic micro-organisms (usually harmless organisms, with a role in protection from
  pathogens)
• May cause disease in immunosuppressed individuals (eg. AIDS sufferers, patients immunosuppressed
  with drugs after transplantation or people with inherited immunodeficiencies)

Question 7

Innate mechanisms of defence against infectious disease

Answer 7

• Can act without help from the specific immune response
• Includes physical barriers to infection: mucus, gastric acid, bile salts, normal flora

Effector functions:

• Respiratory burst → neutrophils, monocytes, macrophages
• Degranulation → mast cell, eosinophils, basophils
• Phagocytosis and phagolysosomal degradation → neutrophils, macrophages
• Opsonin-associated functions → neutrophils and macrophages
• NK cells
• Soluble molecules → complement, interferons and other secreted molecules

Question 8

Example of innate immune evasion strategies

Answer 8

Avoidance of phagocytosis by capsules (e.g. Streptococcus)

Question 9

Describe induction of adaptive immune response

Answer 9

• Depends on T and B lymphocytes
• Involves recognition of an antigen – response is specific for an individual antigen; clonotypic
  distribution of antigen receptors
• The specific response arises by the selection, clonal expansion, and differentiation of lymphocytes that
  recognise the antigen
• Immunological memory for a specific antigen involves:
   The primary response to an antigen
   The secondary response (faster and more effective) to the same antigen

Question 10

What do T cell recognise?

Answer 10

Peptide antigens presented by MHC molecules

Question 11

What do B cells recognise?

Answer 11

A wide variety of native antigens

Question 12

Describe effector mechanisms of adaptive immunity

Answer 12

B cells
- B cells differentiate to antibody-secreting cells (plasma cells)
- Antibodies:
 Prevent entry of pathogens (eg. viruses and mucosal bacteria)
 Neutralise bacterial toxins
 Opsonise bacteria
 Initiate acute inflammation via complement cascade (‘classical pathway’)
T cells
- T cells:
 Help B-cells grow and differentiate to plasma cells
 Kill cells directly (eg. virus-infected cells)
 Secrete cytokines which, for example, activate macrophages and NK cells (so improving the
effectiveness of innate immunity)