CSIM1.17: Innate and acquired immunity

Question 1

What is a pathogen?

Answer 1

Micro-organisms that cause pathology

Question 2

What’s our first line of defence against pathogens?

Answer 2

Barrier mechanisms like skin, gut, lungs and eyes/nose

Question 3

Describe the barrier mechanisms that we have

Answer 3

Epithelial cells joined by tight junctions
Movement of air/fluid
Movement of mucus by cilia
Enzymes/low pH/acids
'Normal flora'

Question 4

Describe ‘normal flora’ and how it forms a barrier

Answer 4

Non-pathogenic bacteria in the right places, i.e. will be pathogenic in the blood

They compete with pathogens for nutrient and produce antimicrobial substances

Question 5

What happens when our barrier mechanisms are breached?

Answer 5

Our innate immunity takes action and is our 2nd line of defence

Question 6

Macrophage is a type of phagocyte. What are macrophages called in: 1. blood, 2. liver, 3. skin, 4. CNS, 5. lungs?

Answer 6

1. monocytes
2. kupffer cells
3. Langerhans cells
4. microglial cells
5. alveolar macrophages

Question 7

Where do macrophages come from?

Answer 7

They mature from blood monocytes and live in tissues

Question 8

Are neutrophils (polymorphonuclear leukocyte PMN) usually found in healthy tissue? Why?

Answer 8

No; they’re confined to the bloodstream until there is a problem (infection/inflammation) and they will travel to the affected site

Question 9

How do phagocytes distinguish self from non-self?

Answer 9

Microorganisms bear repeating patterns of molecular structure called pathogen-associated molecular patterns (PAMPs) that differ than those of human cells, allowing phagocyte receptors to recognise pathogens directly through pattern-recognition receptors (PRR)

PRR bind to PAMPs

Question 10

What happens in phagocytosis?

Answer 10

1. Pathogen is surrounded by phagocyte membrane
2. Internalised in membrane-bounded vesicle (phagosome or endocyte vacuole)
3. Phagosome then becomes acidified and this kills most pathogens

Question 11

Describe the biochemical mechanism of phagocytosis.

Answer 11

NADPH oxidase -> superoxide anion O2-

With help of enzyme superoxide dismutase:
O2- => H2O2 (hydrogen peroxide)

WIth help of peroxidase enzymes and iron: H2O2 => OCl- and OH radicals

OCl- and OH radicals are highly toxic and they kill the bacteria

Question 12

Describe phagolysosome.

Answer 12

Fusion of phagosome and lysosome creates phagolysosome and lysosome contents destroy pathogen

Question 13

Describe mechanisms that pathogens develop to overcome phagocytes.

Answer 13

1. Having structures not recognised by cell receptors
   e. g. Pneumococcus, meningococcus have polysaccharide structures
2. Hide and grow inside macrophages until host is immunocompromised (latent infection)

Question 14

What do Toll-like receptors do?

Answer 14

Bind to pathogens and activate NF kappa-B protein => controls transcription of DNA for protein and cytokine production => induces secretion of pro-inflammatory cytokines

Recognise elements of MOST microbes