Innate killing Mechanism

Question 1

Secretory molecules

Answer 1

enzymes/proteins that are secreted into lumen of tissue (extracellular) into cornea, saliva, lumen of gut or into skin, and control microbe growth. Can be secreted by cells of the innate immune system or epithelial cells.

Question 2

Lysozyme

Answer 2

secreted in fluids of cornea, saliva and gut (Paneth cells)

– breaks down peptidoglycan, a component of the bacterial cell wall

Question 3

Phospholipase A2

Answer 3

– breaks down phospholipids in cell membrane of bacteria

Question 4

Examples of Antimicrobials peptides

Answer 4

Defensins, Cathelicidins, Histatins, Lecticidins

Question 5

Defensins

Answer 5

(alpha-defensins in Paneth cells of the intestinal tract and beta-defensins in lung and skin) – disturb the cell membrane of bacteria and fungi

Question 6

Cathelicidins

Answer 6

antimicrobial defensins produced by activated neutrophils and epithelial cells

Question 7

Histatins

Answer 7

(oral cavity, active against fungi)

Question 8

Lecticidins

Answer 8

creates a pore in microbial cell membranes)

Question 9

Complement exists in

Answer 9

fluids and blood

Question 10

Roles of complement

Answer 10

– capable of direct killing of pathogens through membrane attack complex (MAC)
– also potentiates phagocytosis and the recruitment of other inflammatory mediators

Question 11

What is complement?

Answer 11

Number of small proteins that are synthesized by the liver, tissue macrophages, blood monocytes, and epithelial cells of the genitourinary system and gastrointestinal tract. These small proteins circulate in the blood as inactive precursors. These circulate in blood and can diffuse into tissues

Question 12

3 Phases of Alternative Complement Cascade

Answer 12

1) Activation
2) Amplification loop
3) Effector functions

Question 13

Overview of Alternative Complement

Answer 13

• Spontaneous low level activation
• If deposited onto pathogen = Activation
• If deposited into host cell = Inhibited

Question 14

Complement cascade membrane attack complex (MAC)

Answer 14

• C5b binds to other components of cascade; c6, c7, c8 and c9
• C9 oligomerises which forms a pore around the membrane forming a channel of consecutive units
• When this occurs on bacterial cell then it has a pore in its membrane, which are visible as rings in the bacterial membrane, if you look at a side view you can see tubes.
• Creating pores and directly killing the pathogens.

Question 15

How to prevent damage of complement?

Answer 15

• activation of complement is highly regulated
• to prevent complement-mediated damage of normal host cells
• The same regulatory mechanisms exist for many other killing mechanisms

Question 16

Intracellular Killing Mechanims = phagocytosis is a very

Answer 16

• ancient process: means eating (or kills an invader)

* Example: Amoeba eats a paramecium

Question 17

Where does phagocytosis mostly occur?

Answer 17

in neutrophils and in monocytes/macrophages/dendritic cells (creates harsh environment for microbes)

Question 18

Phagosome killing

Answer 18

• The phagolysosome is matured through sequential fusion with endosomes and lysosomes and becomes a very specialized intracellular compartment
• very unpleasant environment for microbes

Question 19

Phagocytosis - microbes recognised by phagocytic surface receptors (2 ways)

Answer 19

PAMPS - PRR

and Opsonisation

Question 20

Opsonisation (2 types)

Answer 20

1. Microbe coated with complement = binds CR3-CR4

2. Microbe coated with antibody = antibody binds FcReceptors

Question 21

Recognition via PRR-PAMPS and Opsonisation causes

Answer 21

subsequent signalling which trigger PHAGOCYTOSIS (ingestion process + subsequence maturation of the compartment which is formed in the cell)

Question 22

Phagosomal Maturation

Answer 22

• When cells first ingested a microbe with extra cell or milia
• Host cell will manipulate the phagosome to make a harsh environment:
• Endosomes and lysosomes contain enzymes and proteins that will fuse with phagosome to change its composition to create a harsh environment.
• RAB5 positive endosomes fuse with nascent phagosome (early phagosome)
• Followed by endosomes that have EEA1 fusing to create intermediate phagosome.
• After EEA1 is in the intermediate phagosome, the phagosome loses its RAB5, signaling RAB7 to start merging with a phagosome and is now known as the late Phagosome.
• Lysosomes deliver hydrolytic enzymes which exist in the fibre lysosome.
• At the same time, the endosomes fuse + they deliver components into the lumen into the interior of the vacuole which is the phagosome
• Lots of molecules in the membrane (transporters) which help create this environment i.e.
  o Acidity

Question 23

Acidity in Phagosomal maturation

Answer 23

= the V-ATPase proton channel will start pumping H+ ions into the phagosome to make it acidic, once the lysosomal enzymes, the acidic hydrolyses fuse then they become activated but they only work in acidic pH

Question 24

Overview of phagosomal maturation

Answer 24

Overview:
• The phagolysosome is matured through sequential maturation with lysosomes and becomes a very specialized intracellular compartment with:
• Low pH (pH=4.5): mediated by a V-ATPase proton channel
• Accumulation of reactive oxygen species (NADPH oxidase - subunit gp91 or NOX2, and others)  oxidative stress
• Accumulation of nitric species (iNOS)  nitrosative stress
• Antimicrobial enzymes : cathelicidins, defensins, acid hydrolases, which are secreted into lumen of phagosome.
• Low nutrients: no sugars, no micronutrients (Fe, Cu, Zn, etc), which are pumped out of the phagosome or sequestered (lactoferrin).
• Phagosome maturation to phagolysosome takes 30-60 min.

Question 25

Phagosome killing and more - phagocytosis mostly occur in

Answer 25

neutrophils and in monocytes/macrophages/dendritic cell. Different phagosomes for each of the cell types

Question 26

Phagosome killing and more - what are the major differences between cell types

Answer 26

• In dendritic cells, phagosome is adapted to perform antigen presentation: to degrade antigens and load them to bridge adaptive immunity.
• In neutrophils, due to their specific granules phagosome is basic (pH=8 for about 30 min) to facilitate optimal activity of elastase and cathepsin G.

Question 27

Granules

Answer 27

collections of enzymes which have proteins which don’t necessarily exist in macrophages.