Immunology of gut

Question 1

what is the surface area of the gi tract

Answer 1

200m^2

Question 2

what is the antigen load in gi tract

Answer 2

resident microbiota 10^14 bacteria
dietary antigens
exposure to pathogens

Question 3

what is meant by state of ‘restrained activation’ in gi tract

Answer 3

has to balance tolerance with active immune response
tolerate: food antigens and commensal bacteria
immunoreactivity against: pathogens

Question 4

what is the gut microbiota

Answer 4

considered a virtual organ
4 major phyla of bacteria - bacteroidetes, firmicutes, actinobacteria, proteobacteria, also viruses and fungi
provide traits we have not had to evolve on our own

Question 5

what is dysbiosis

Answer 5

altered microbiota composition

Question 6

what are some causes of dysbiosis

Answer 6

infection and inflammation
diet
xenobiotics
hygiene
genetics

Question 7

what are the physical barriers against pathogens

mucosal defence

Answer 7

anatomical - epithelial barriers and peristalsis

chemical - enzymes and ph

Question 8

how does the epithelial barrier defend against pathogens

Answer 8

mucus layer - goblet cells
epithelial monolayer - tight junctions
paneth cell(small intestine) in bases of crypts of lieberkuhn
- secrete antimicrobial peptides and lysozyme

Question 9

what is commensal bacteria

Answer 9

occupy ecological niche and act as barrier itself

Question 10

what are some immunological defenses following invasion

Answer 10

malt - mucosa associated lymphoid tissue

galt - gut associated lymphoid tissue

Question 11

what is malt

Answer 11

• found in submucosa below epithelium as lymphoid mass containing lymphoid follicles
• follicles are surrounded by HEV postcapillary venules - allowing easy passage of lymphocytes

Question 12

what is galt

Answer 12

responsible for both adaptive and innate immune response through generations of lymphoid cells and antibodies

Question 13

what are some examples of non organised galt

Answer 13

intra epithelial lymphocytes

lamina propria lymphocytes

Question 14

what are some examples of organised galt

Answer 14

peyers patches(si)
caecal patches(li)
isolated lymphoid tissues
mesenteric lymph nodes - encapsulated

Question 15

what are peyers patches

‘immune sensors’

Answer 15

found in submucosa of small intestine - mainly distal ileum
- aggregated lymphoid follicles covered with follicle associated epithelium
fae - no goblet cells, no secretory igA and lack microvilli

Question 16

what is found in peyers patches

Answer 16

collection of naive t cells and b cells

• development requires exposure to bacterial microbiota
• 50 in last trimester foetus and 250 by teens

Question 17

how does antigen uptake via peyers patches take place

Answer 17

via microfold cells within FAE

M cells express igA receptors - facilitating transfer of igA bacteria complex into peyers patches

Question 18

what is the b cell adaptive response

Answer 18

mature naive b cell expresses igM in PPs
on antigen presentation class switches to igA
- t cells and epithelial cells influence b cell maturation via cytokine production
b cells further mature to become igA secreting plasma cells
populate lamina propria

Question 19

what immunoglobulin do upto 90% of gut b cells secrete

Answer 19

igA

secretory IgA binds luminal antigen - preventing its adhesion and consequent invasion

Question 20

why do enterocytes and goblet cells have short life span

Answer 20

can be directly affected by toxic substances in diet

- lesions will be short lived as responded to

Question 21

what is the mechanism of cholera

Answer 21

acute bacterial disease caused by vibrio cholerae serogroups o1 and o139
- bacteria reaches small intestine - contact with epithelium and releases cholera enterotoxin

Question 22

how is cholera transmitted

Answer 22

through faecal oral route

spreads via contaminated water and food

Question 23

what are the main symptoms of cholera

Answer 23

severe dehydration and watery diarrhoea

other symptoms: vomitting, nausea and abdo pain

Question 24

what is the diagnosis for cholera

Answer 24

bacterial culture from stool sample on selective agar is gold standard, rapid dipstick tests also available

Question 25

what is the treatment for cholera

Answer 25

oral rehydration is main management - upto 80% cases can be successfully treated vaccine - dukoral, oral and inactivated globally : 1.3 - 4 mill cases

Question 26

what are some viral causes of diarrhoea

Answer 26

rotavirus | norovirus - winter vomiting bug

Question 27

what are some bacterial causes of diarrhoea

Answer 27

``` campylobacter jejuni escherichia coli salmonella shigella c. diff ```

Question 28

what are some protozoal parasitic casues of diarrhoea

Answer 28

giardia lamlia | entamoeba histolytica

Question 29

what are rota viruses

Answer 29

rna virus - replicates in enterocytes | 5 types: A is most common in human infections

Question 30

what is the treatment for rotaviruses

Answer 30

oral rehydration therapy still causes ~ 200000 deaths/yr vaccine - live attentuated oral vaccine against ype a

Question 31

what is the norovirus

Answer 31

rna virus | incubation period 24-48 hrs

Question 32

how is norovirus transmitted

Answer 32

faecal oral transmission individuals may shed infectious virus for upto 2 wks outbreaks often occur in closed communties

Question 33

what are the symptoms of norovirus

Answer 33

acute gastroenteritis

Question 34

how to diagnose norovirus

Answer 34

sample pcr

Question 35

what are the most common species of campylobacter

Answer 35

c. jejuni and c. coli

Question 36

how is campylobacter spread

Answer 36

undercooked meat esp pultry untreated water unpasteurised milk low infective dose

Question 37

what is treatment for camylobacter

Answer 37

non required usually azithromycin resitance to fluoroquinolones is problematic

Question 38

what is e coli

Answer 38

diverse group of gram neg intestinal bacteria most harmles 6 pathotypes associated with diarrhoea

Question 39

what is the management for c diff

Answer 39

isolate patient stop current antibiotics give metronidazole and vancomycin recurrence rate 15-35%, increasingly hard to treat faecal microbiota transplantation - 98% cure rate