Lecture 6 - Bacterial immunity

Question 1

What sort of molecules are recognised by the innate system?

Answer 1

Molecules that are common to bacteria but absent from the host (PAMPS)

Question 2

What is the membrane attack complex?

Answer 2

C9 forms a pore and inserts into bacterial cell membranes. It promotes cell lysis.

Question 3

A deficiency in C1q of the complement cascade, leads to increased susceptibility to what?

Answer 3

Sepsis, meningitis, pneumonia

Question 4

A deficiency in C3 of the complement cascade, leads to increased susceptibility to what?

Answer 4

Respiratory tract infections and meningitis

Question 5

A deficiency in C5 of the complement cascade, leads to increased susceptibility to what?

Answer 5

Meningitis and sepsis

Question 6

A deficiency in C9 of the complement cascade, leads to increased susceptibility to what?

Answer 6

Meningitis and sepsis

Question 7

What is involved in the process of indirect bacterial recognition?

Answer 7

Bacteria coated with antibodies are recognised by AB receptors (e.g. Fc receptors)
*Bacteria coated with C3b are recognised by C3b receptors

Question 8

What is involved in the process of direct bacterial recognition?

Answer 8

PAMPs are recognised by PRRs e.g. TLRs

Question 9

Describe the rough structure of a TLR (toll like receptor)

Answer 9

They have an extracellular domain required for ligand recognition and an intracellular domain for signalling.

*dimerisation is also essential for signalling

Question 10

What are the consequences of binding to phagocytes?

Answer 10

Activation of pathways leading to cytokine and chemokine production
Ingestion and killing

Question 11

What is the action of IL-1?

Answer 11

Activates endothelial cells and important in fever

Question 12

What is the action of IL-6?

Answer 12

Proliferation of AB producing B cells

Question 13

What is the action of TNF-a?

Answer 13

Activates endothelial cells, important in fiver and activates neutrophils

Question 14

What is the action of INF a?

Answer 14

Antiviral immunity, promotes CD4 and CD8 T cell responses

Question 15

What is the action of IFN b?

Answer 15

Antiviral immunity, promotes CD4 and CD8 T cell responses

Question 16

What is the name of the process by which bacteria recognised by TLRs are killed?

Answer 16

Phagocytosis

Question 17

What are the 5 steps in the process of phagocytosis?

Answer 17

1. Bacteria recognised by phagocyte via its TLR
2. Recognition triggers uptake of bacteria into phagosome, where bacterial killing takes place.
3. This phagosome fuses with a lysosome to form the phagolysosome
4. The internalised bacteria is broken down in the phagolysosome
5. Soluble debris are released via exocytosis

Question 18

What does the adaptive system recognise?

Answer 18

Antigens (motifs) that are unique to an individual pathogen, most commonly proteins and polysaccharides

Question 19

Name 4 bacterial diseases where CD8 T cells play a role in protection

Answer 19

Tuberculosis
Salmonellosis
Listeriosis
Meliodosis

Question 20

What are the downstream affects of CD4+ t helper cell activation?

Answer 20

Il-17 and TNF (amongst others) cause inflammation
IFNg causes macrophage activation which leads to phagocytic bacterial killing
Various cytokines activate B cells/ plasma cells in order to produce an AB response

Question 21

What is agglutination?

Answer 21

Antibodies mark bacterial cells and cause them to stick together (agglutinate) meaning they are more efficiently cleared by phagocytes

Question 22

What is neutralisation?

Answer 22

ABs are capable of binding to and ‘neutralising’ toxins. If toxins are central to the disease process then ABs that neutralise the toxin block the disease

Question 23

What is opsonisation?

Answer 23

Antibodies bind to bacteria and make them more ‘visible’ to phagocytes. ABs bound to bacteria promote their uptake and killing by phagocytosis.