Immunology 2- Phagocytosis and innate responses

Question 1

What is opsonisation?

Answer 1

The coating of pathogens by opsonins to enhance phagocytosis.

Question 2

What is phagocytosis (general)?

Answer 2

The internalisation of particles such as bacteria . It facilitated by opsonisation and is done by innate immune cells including macrophages.

Question 3

Describe phagocytosis.

Answer 3

1. Macrophages’ PPRs bind to PAMPs
2. Formation of a phagocytic cup is stimulated
3. The cup extends around the target and pinches off , forming a phagosome.
4. Phagosome fuses with lysosomes to form a phagolysosome, which kills pathogens and degrades the contents by acidification and lysosomal hydrolases
5. Debris (including antigens) is released into extracellular fluid
6. Pathogen-derived peptides ae expressed on special cell surface receptors called MHC-II molecules

Question 4

Macrophages can only digest one bacteria at a time. True or false?

Answer 4

False.

Question 5

Describe mast cells.

Answer 5

• have PRRs
• contain degrative enzymes
• they recognise pathogens and danger signals
• they perform degranulation ( release of pre-formed pro-inflammatory substances e.g. histamine)
• also perform gene expression- (production of new pro-inflammatory substances e.g. prostaglandins)

Question 6

What do pro-inflammatory mediators do?

Answer 6

Promote localised, acute inflammation.

Question 7

What are physiological signs and symptoms of acute inflammation?

Answer 7

Symptoms:

• redness
• heat, may lead to fever
• swelling
• Pain
• loss of function

Physiological signs:

• vasodilation
• Increased permeability of capillaries
• stimulation of nerve endings

Question 8

What are neutrophils?

Answer 8

They are killer white blood cells which perform phagocytosis. They are attracted to tissues by chemical signals released by pathogens. Also produce pro-inflammatory mediators like TNFa.

Question 9

What is transendothelial migration?

Answer 9

The recruitment and activation of neutrophils.

Question 10

Describe the process of transendothelial migration.

Answer 10

1. Neutrophils are at the endothelium near sites of infected tissue.
2. Neutrophils bind to adhesion molecules (selectins then ICAM-1) on the endothelial cells
3. Neutrophils migrate across the endothelium via diapedesis
4. Movement of neutrophils within the tissue via chemotaxis.
5. Neutrophils activated by PAMPS and TNFa

Question 11

What mechanisms can neutrophils use to kill pathogens?

Answer 11

• phagocytosis
• ROS- dependent killing (produces toxic reactive oxygen species)
• degranulation
• netosis (spew out the contents of the nuclei and also granules etc., forming sticky NETs which trap cells in an extracellular environment )

Question 12

What are macrophages?

Answer 12

Cells which perform phagocytosis and produce pro-inflammatory mediators like TNFa.

Question 13

What is the acute phase response?

Answer 13

A systemic response which involves changes in the plasma concentrations of specific proteins in response to inflammation. It is driven by pro-inflammatory mediators released by activated macrophages. It is mediated by liver hepatocytes which produce a variety of acute phase proteins e.g. C3 and C reactive protein.

Question 14

What is C reactive protein?

Answer 14

An acute phase protein in humans used as a marker for inflammation. It has a short life, and measuring levels of CRP can lead to diagnosis.

Question 15

What do virally infected cells release (hint: detected byNK cells)

Answer 15

Produce and release cytokines called interferons. Slows down viral reproduction. Can also act as signalling cells to neighbouring cells.

Question 16

Describe how Natural Killer (NK) cells kill virally infected/cancer cells and pathogens.

Answer 16

Healthy cells show a ‘don’t kill me’ on their cell surface called MHC I. NK cells will kill any cell it comes across that does not express MHC I.

Question 17

What is TNFalpha?

Answer 17

A type of cytokine/pro-inflammatory mediator which stimulates acute inflammation.