Lecture 11. The Cellular Arm of the Innate Immune Response

Question 1

What are the three major classes of phagocytes?

Answer 1

Neutrophil, Eosinophil, Macrophage

Question 2

What are neutrophils and Eosinophils?

Answer 2

Granulocytes: named because their cytoplasm is granular

Question 3

What do neutrophils do?

Answer 3

They phagocytose and destroy microorganisms, especially bacteria, and thus have a key role in innate immunity to bacterial infection

Question 4

What are properties of neutrophils?

Answer 4

Short-lived cells
Abundant in blood
Not present in normal healthy tissues

Question 5

What are neutrophils rapidly recruited by?

Answer 5

Activated macrophages
Peptide fragments of cleaved complement proteins
And by some PAMPs

Question 6

How do macrophages function?

Answer 6

They recognise and remove senescent, dead, and damaged cells in many tissues, and are able to ingest large microorganisms such as protozoa

Question 7

What do Eosinophils help to do?

Answer 7

Destroy parasites, modulate allergic inflammatory responses

Question 8

What is it called when a phagocyte’s plasma membrane surrounds the pathogen and engulfs and encloses it?

Answer 8

Phagosome

Question 9

What are ‘granules’?

Answer 9

Dense membrane-bound lysosomal derivatives
They fuse with the phagosome membrane and release their contents (lysozyme, acid hydrolases) in an attempt to digest the pathogen’s cell walls

Question 10

What is a respiratory burst?

Answer 10

A transient increase in oxygen consumption

Question 11

What does NADPH oxidase complexes do to phagosomes?

Answer 11

Produce highly toxic oxygen-derived compounds such as superoxide, hypochlorite and hydrogen peroxide after a respiratory burst

Question 12

What do dead neutrophils and pathogens form?

Answer 12

Pus

Question 13

How does inflammation aid in the killing frenzy?

Answer 13

Blood vessels dilate, leading to local swelling and the accumulation of components of the complement cascade

Question 14

What can go wrong with inflammation?

Answer 14

Systemic release of inflammatory cytokines can lead to excessive blood vessel dilation, resulting in sudden lowering of blood pressure (shock)
If widespread inflammation, septic shock can occur

Question 15

What does dsRNA do?

Answer 15

Induces interferon (IFN) production

Question 16

What are interferons?

Answer 16

Interferons are the most important cytokines in the virology context: IFN-α and IFN-β are produced by all cells in response to viral dsRNA

Question 17

What do interferons do?

Answer 17

1. Make the virally-infected cell and its neighbours into much less efficient factories for making new viruses
2. Limit viral spread by promoting apoptosis (programmed cell death – in a couple of slides) of the infected cell
3. Upregulate the display of viral peptides on the outer membrane of the infected cell: this provides signals for recognition by activated T cells
4. Stimulate expression of the immunoproteasome to process and destroy viral proteins
5. They also provide a call for help, attracting natural killer cells and also activating macrophages
6. They also fight cancers

Question 18

What do natural killer cells do?

Answer 18

NK cells recognise their targets by monitoring the level of expression of these molecules at the cell surface
NK cells are also attracted to virally-infected cells by IFNs
NK cells then persuade such cells to commit suicide: the target cells die by apoptosis

Question 19

Process of NK cells persuading apoptosis

Answer 19

Apoptopic signals given
Mild convolution, chromatin compaction, cytoplasmic condensation
Nuclear fragmentation, cell ‘blebbing’, cell fragmentation
Phagocytosis