Immune cells

Question 1

What are macrophages?

Answer 1

remove cellular debris
defence against microbial infection
monoctyes differentiate into macrophages

Question 2

What happens during phagocytosis?

Answer 2

takes up particles >0.5um
surrounded by plasma membrane-derived membrane
form phagosome
phagolysosome

Question 3

How is phagocytosis receptor mediated?

Answer 3

phagocytosis is triggered by the recognition of microorganisms by receptors on macrophage surface

PRR e.g. CD36, mannose receptor

opsonic receptors e.g. Fc receptors, complement receptors

Question 4

How is phagocytosis initiated?

Answer 4

IgG receptor FcyRIII binds IgG opsonised microorganisms

clustering = phosphorylation of ITAM motifs by Src protein kinases

Syk protein kinase recruited - promote phagocytosis - small GTPases = key downstream targets

Question 5

How is the phagosome formed?

Answer 5

actin cytoskeleton = central role

GTPases interact with WASP = activates Arp2/3 actin filament formation in FcyR receptor = phagocytosis

pseudopods form phagosome

Question 6

How are phagosomes matured?

Answer 6

sequential fusion of early endosomes, late endosome and lysosomes

contents become more acidic

Rab5, Rab7 - recruit other proteins onto membrane

moves to perinuclear location

Question 7

What are the antimicrobial activities of the macrophage phagolysosome?

Answer 7

lactoferrin - nutrient deprivation

defensins - membrane permeable

Hydrolases

Production of ROS an RNS

acidification

Question 8

How does tuberculosis evade macrophage killing

Answer 8

arrests phagosome maturation

Rab5 fails to recruit other proteins onto membrane

SapM hydrolyses

Phos. mannoside promotes fusion of early endosome with M.tub containing phagosomes

Question 9

How do IFN-y promote macrophage killing of M. tuberculosis?

Answer 9

IFN-y releasec by T cells and NK cells

induces macroautophagy of M.tuberculosis arrested phagosomes

delivered to lysosomes

Question 10

How do listeria evade microbial killing?

Answer 10

Listeriolysin O (LLO)
pores in phagosome - H+ and Ca2+ escape = no fusion of phagosome with endosome

Produces phospholipases - breakdown of phagosome membrane

Question 11

What do CTLs do?

Answer 11

kill abnormal cells
T cell receptor on CTLs recognise peptides presented by MHC class I
triggers exocytosis of secretory lysosomes
perforin facilitates entry of granzymes - induce apoptosis

Question 12

What are secretory lysosomes?

Answer 12

dual function organelles

degradative function & capacity for regulated exocytosis

contain lysosomal hydrolases, lysosomal transporters & acidic pH

Question 13

What is the 3 stage CTL secretory lysosome exocytosis process?

Answer 13

1) immunological synapse formed
2) MTOC & secretory lysosomes polarise towards immunological synapse
3) secretory lysosomes dock & fuse with the plasma membrane at immunological synapse & release contents

Question 14

How are SNAREs involved in secretory lysosome fusion?

Answer 14

catalysed by SNAREs

form a trans-SNARE complex - drives fusion of 2 membranes

Question 15

How can impaired CTL cytotoxity cause disorders?

Answer 15

loss of CTL function = inflammatory condition

cannot resolve viral infections

Question 16

What is FHL-2?

Answer 16

mutations in perforin

impairs delivery of granzymes into the target cells

Question 17

What is Griscelli Syndrome type 2?

Answer 17

mutations in GTPase Rab27a
partial albinism due to defects in melanosomes
secretory lysosomes cluster around MTOC at synapse but do NOT fuse
suggests Rab27a is required for docking

Question 18

What is FHL-3?

Answer 18

mutations in Munc13-4
can dock but do not fuse
suggest Munc13-4 has role prior to SNARE mediated fusion

Question 19

What is FHL-4?

Answer 19

mutations in syntaxin 11
dock but cannot fuse
can be restored by treatment with IL-2 which induces expression of another SNARE syntaxin-3