Innate Response

Question 1

Ways complement system can be activated

Answer 1

Classical pathway, Mannose-binding lectin pathway, alternative pathway

Question 2

Classical pathway

Answer 2

Only occurs when there are antibodies specific to a foreign antigen

Antibody complexes bound by component C19 detects bound antibodies to pathogens

Activates subsequent complement components

Question 3

Mannose-binding lectin

Answer 3

Mannose is a carbohydrate not present on self cells but often on bacteria cells

Activation through mannose-binding lectin binding to mannose on bacteria

Question 4

Alternative pathway

Answer 4

Involves complement component C3 - which spontaneously activates and binds to nearby membranes

Host cells have control proteins on their surface to prevent further complement activation by degrading C3

Bacterial cells do not have control proteins so the complement is activated via further activation of C3 proteins

Question 5

Result of complement activation

Answer 5

Complement lysis

Question 6

Complement lysis

Answer 6

Membrane attack complex MAC forms in membrane of bacteria

Barrel like structure is formed from multiple late complement components (C6-C9)

This disrupts osmotic balance as the semi-permeable membrane is destroyed —> water rushes in, ions rush out, bacteria swells and bursts

Question 7

Complement components

Answer 7

Soluble complement proteins are released on complement activation —> their release helps trigger immune response and amplify inflammation by causing blood vessels to become leaky -> resulting in recruitment of immune cells and activation of mast cells

Question 8

Opsonisation

Answer 8

Activated by membrane bound complement components

Complement component binds to bacteria -> phagocytes have complement receptor which bind membrane bound component -> encourages phagocytosis by switching on killing mechanisms

Question 9

Phagocytes

Answer 9

Neutrophils, macrophages, dendritic cells

Question 10

Neutrophils

Answer 10

Good at killing - kill as much as possible, use so much energy that they then die very quickly

Recruited rapidly to site of infection

Very short lived

Constituent of pus

Question 11

Macrophages

Answer 11

Reside in tissue

Good at killing if activated

Also involved in tissue healing, clearance of dead cells and metabolism

Question 12

Dendritic cells

Answer 12

Initiate adaptive immune responses

Reside in tissues

Poor at killing

Question 13

Extravasion

Answer 13

How neutrophils get to the site of inflammation from the circulation

Endothelium of blood vessel altered by inflammatory cytokines so neutrophil can loosely associate, ROLLING ADHESION —> neutrophil tightly adheres to endothelium TIGHT BINDING —> neutrophil overs through epithelium, only occurs where there is inflammation as creates leaky epithelium DIAPEDESIS ->MIGRATION of neutrophils up the chemokine gradient to the site of infection

Question 14

Phagocytosis

Answer 14

Phagocyte detects pathogen and engulfs it —> forms phagocyte —> Lysosome (contains toxic products) fuses with phagosome to form PHAGOLYSOSOME —> phagolysosome matures as more lysosomes fuse with it —> hydrogen ions are pumped in —> protease, oxygen radicals, nitric oxide degrade pathogen

Question 15

Macrophage Activation

Answer 15

Macrophages can uptake bacteria before activation - but require activation in order to engage in phagocytosis

Macrophages are activated via danger signalling or via cytokines —> especially interferon gamma

Question 16

Neutrophil Extracellular Traps

Answer 16

Neutrophils can extrude their DNA, acting like a net - to stop pathogens spreading through he body by trapping them

Question 17

Antigen presentation

Answer 17

Dendritic cells sense danger —> they mature and upregulate different chemokine receptors —> resulting in migration to the lymphatics and draining lymph node —> Present antigen to T-cells

Question 18

Dendritic cells migrate

Answer 18

Into T-cell area to find the random specific antigen receptor

Question 19

B-cell receptor

Answer 19

Can recognise soluble antigen in its normal form

Question 20

T-cell receptor

Answer 20

Has to have antigen ‘presented to it on Major Histocompatibility Complex (MHC) on another cell

Antigen must be chopped up into peptides as T cells can’t recognise full protein

Question 21

Antigen presentation with no danger signal

Answer 21

Results in no response prevents autoimmunity

Question 22

Antigen presentation with danger stimuli

Answer 22

Needs to have danger stimuli (co-stimulation), cytokine storm and antigen presentation in order to trigger an immune response