Innate immunity

Question 1

basic overview of innate IS

Answer 1

non-specific

rapid

always active

physical + chemical barriers

Question 2

basic overview of adaptive IS

Answer 2

specific

slower

forms immune memory

cellular and humoral responses

generates Abs

Question 3

first line of defence

Answer 3

innate immunity mechanisms constitutively produced

• physical, chemical and microbiological
• secreted antimicrobial agents

Question 4

second line of defence

Answer 4

innate immunity mechanisms mobilised if pathogens breach first line defences

Question 5

third line of defence

Answer 5

adaptive immune response

- for small minority of infections innate immunity can’t control

Question 6

constitutive epithelial defences

Answer 6

mechanical/chemical barriers
- skin, mucous production, low pH, osmotic stress etc.

constitutive antimicrobial defences
- enzymes e.g. lysozyme, fatty acids, antimicrobial peptides

bacterial/commensal microbial interactions
- niche competition, AB production by commensals

Question 7

constitutive humoral defences

Answer 7

blood clotting
- seals wounds, traps microbes + activates other aspects of immunity

complement system
- labels + kills microbes, activates other aspects of immunity

Question 8

surface epithelia barriers

• mechanical
• chemical
• microbiological

Answer 8

> epithelial cells joined via tight junctions
longitudinal flow of air/ fluid

> fatty acids
antimicrobial peptides

> normal microbiota

Question 9

skin’s defence mechanisms

- epidermis

Answer 9

constant sloughing of keratinocytes

lysozyme + high salt (acidic) in sweat

commensal microbes competitively exclude pathogens by secreting fatty acids

waxy, water resistant coating
- protects against damage + keeps dry

Question 10

skin’s defence mechanisms

- dermis

Answer 10

defensins

RNases + DNases

phagocytes e.g. neutrophils + macrophages

Question 11

peptidoglycan

• structure
• glycan structure

Answer 11

linear glycan strands cross-linked by peptide chains

N-acetylglucosamine
N-acetylmuramic acid
joined by beta 1-4 glycosidic links

Question 12

lysozyme

• what is it?
• mechanism

Answer 12

antimicrobial enzyme
- in tears, saliva, sweat etc

destroys peptidoglycan 
-> exposes lipid bilayer 
-> bacteria lose rigidity of cell wall
-> osmotic stress
= cell bursts

Question 13

microbiome composition

- differences

Answer 13

between individuals

between different parts of body

Question 14

ways into the skin

Answer 14

sweat glands

hair follicles

Question 15

blood clotting and coagulation

Answer 15

seals breaches in blood vessels + prevents blood loss by forming a fibrin clot

physically traps invading microbes
-> inhibits spread of infection

attracts phagocytic cells

has direct antimicrobial activity e.g. beta-lysine

Question 16

gut barriers

• mechanical
• chemical
• microbiological

Answer 16

> epithelial cells joined by tight junctions
longitudinal flow of air or fluid

> low pH
antimicrobial enzymes

> normal microbiota

Question 17

GI tract barriers

Answer 17

low pH in stomach

mucus layer + fluid flow throughout

proteases, lipases + bile released into duodenum

secretion of antimicrobials

competition by commensal microflora

Question 18

low pH in stomach

• pH
• impacts on cell function

Answer 18

pH 2-5

damage proteins/ impair functions

damage nucleic acids

limit nutrient uptake

kills many pathogens rapidly

Question 19

mucosal epithelium

Answer 19

extra protective layer to tight junctions in epithelia
- prevents pathogens adhering to cells

mucocilliary escalator + resident microflora protect against pathogens

all mucosal sites have fluid flow + resident microflora

Question 20

what also happens in the intestine and bladder/urethra?

Answer 20

intestine = peristalsis

bladder + urethra = peristalsis

Question 21

gut microbiome composition

Answer 21

most extensive

varies along the gut
influence by physiological differences
e.g. higher pH, lower O2 + lower antimicrobials = higher bacterial load

Question 22

competition by commensal microbes

Answer 22

~500 species of bacteria reaching 10^13 cells in colon

colonise upper mucous layer

competitively exclude + produce antimicrobial agents to inhibit pathogen growth + prevent the establishing

Question 23

normal outer and inner mucus layers

Answer 23

outer
- habitat for commensals

inner
- impenetrable to bacteria

Question 24

colitis

Answer 24

inner mucus layer penetrable to bacteria

bacteria contacts with intestinal epithelium

Question 25

Gut Paneth cells produce antimicrobial agents

Answer 25

lysozyme
phospholipase
defensins
lectins

Question 26

antimicrobial peptides

Answer 26

e.g. defensins

kill bacteria by entering crypts to protect stem cells + avoid infection

bind strongly to bacterial membranes due to anionic charge
EITHER
1. forms pores in cell membrane + ruptures cell
2. enters cell + inhibits functions within

Question 27

mucus production + antimicrobial agents

Answer 27

work in conjunction to provide a bacterial exclusion zone

-> maintains appropriate control of commensal microbiome
some are opportunistic pathogens

Question 28

mucus production + antimicrobial agents

- e.g. lectin RegIII proteins

Answer 28

form pores in bacterial membranes

secreted into lower mucus layer if bacteria detected
-> maintains exclusion of bacteria