9. GI immune mechanisms

Question 1

describe 3 immune mechanisms of the intestines

Answer 1

1. epithelium forms physical barrier - coated with GLYCOCALYX of mucins and other glycoproteins: trap bacteria in mucus
2. PANETH CELLS at bottom of crypts: secrete anti-microbial peptides, e.g. defensins and lysozyme
3. GALT comprised of:
   - PEYER’S PATCHES: subepithelial domes containing dendritic cells, macrophages, B cell germinal centres and T lymphocytes
   - MESENTERIC LYMPH NODES: drain lymph from PPs and lamina propria of mucosal vili

Question 2

how are Peyer’s patches specialised for antigen sampling

Answer 2

1. much thinner mucosal layer
2. specialised phagocytic cells - M cells - transport material across epithelial barrier via transcytosis
3. denditic cells - send out processes to trap antigen

Question 3

how do Peyer’s patches promote immune quiescence

Answer 3

i. once antigen-loaded, PP DCs migrate to T cell zone of PP…
ii. stimulate T cell maturation into Treg cells…
iii. Treg cells migrate to lamina propria of vili via lymphatics…
iv. secrete IL-10 which suppresses immune cells in lamina propria and epithelium = IMMUNE QUIESCENCE

Question 4

name 4 functions of the gut microbiome

Answer 4

1. compete with pathogens for attachment sites and resources
2. produce antimicrobial chemicals
3. synthesise vitamins - K and B (esp. B12)
4. fermentation of unused energy substrates

Question 5

name the most common cause of viral gastroenteritis - why is it so infectious

Answer 5

NOROVIRUS

• can be transmitted person-to-person (<100 viral particles), faeco-oral route or via fomite contamination of environment
• viral particles shed in stool and vomitus (can aerosolise)
• resist freezing, temps up to 60deg and alcohol disinfection
• immunity short-lived

Question 6

name important bacterial causes of GE

Answer 6

1. Campylobacter jejuni
2. Escherichia coli
3. Salmonella enterica
4. Shigella

Question 7

name 3 protozoa which can cause GE

Answer 7

1. Giardia lamblia
2. Entamoeba histolytica
3. Cryptosporidium spp.