Immunology of the gut Flashcards
SA of the GI tract?
200m2
What is included in the antigen load of the gut?
resident microbiota
dietary antigens
exposure to pathogens
What is restrained activation?
Gut has to balance tolerance vs active immune response
dual immunological role
Features of the gut microbiota
10^14 gut bacteria - most densely populated ecosystem on Earth
4 major phyla of bacteria + viruses/ fungi
Provide traits that we did not have to evolve on our own (defence/ digestion of certain compounds/ contribute to intestinal architecture)
what is dysbiosis
altered microbiota composition
what are symbionts
organisms that lives with hosts (no benefit or harm to either)
what are commensals
organisms that benefits from association but no effects on host
what are pathobionts
symbionts which have the potential to cause inflammation and disease under certain conditions
What affects equilibrium of the gut microbiota
infection/ inflammation diet xenobiotics hygiene genetics
what are the mucosal defence of the gut?
physical barriers:
(anatomical) - epithelial barrier (mucosal layer by goblet cells + tight junctions) + peristalsis
(chemical) - enzymes + acidic pH
how do commensal bacteria protect
occupy ecological niche
immunological barrier
MALT - lymphoid ass containing follicles (surrounded by HEV postcapillary venules which allow easy passage of lymphocytes)
GALT - organised or non-organised and responsible for adaptive and innate immune responses (eg. peyer’s patches)
what does MALT stand for
mucosa associated lymphoid tissue
what does GALT stand for
gut associated lymphoid tissue
What is non organised GALT
Lamina propria - immune cells of intestine found there
lymphocyte dotted between enterocytes
what are peyer’s patches
Immune sensors
Found in submucosa of small intestine - organised collection of naive T and B cells (development requires exposure to bacterial microbiota)
What is FAE
Peyer’s patched covered by follicle associated epithelium (no goblet cells/ microvilli) - job is to transfer things to the patches
what are trans-epithelial dendritic cells
DC which can open tight junctions - sample bacteria and bring them back to mesenteric lymph nodes
what is the B cell adaptive response
B cells express IgM in peyer’s patches and on antigen presentation - switch to IgA (B cells mature to become IgA secreting cells)
- antibodies then populate lamina propria for defence
what is lymphocyte homing
mesenteric lymph node
what is the life span of enterocytes/ goblet cells
36 hrs
Why do GI cells have a short turnover
first line of defence against GI pathogens
So any lesions will be short lived due to high turnover
what is cholera
bacterial infection caused by serogroups O1 and O139
Bacteria reaches small intestine + releases cholera enterotoxin
mechanism of cholera
Severe dehydration + diarrhoea (cholera toxin activated cAMP which causes release of excretion of salts and water follows)
what is rotavirus
RNA virus - replicate in enterocytes
Type A is most common type from A-E
Most common cause of diarrhoea in infants worldwide
what is norovirus
RNA virus
Individuals can remain infectious for up to weeks
Acute gastroenteritis
(cause for outbreaks in closed communities)
How to treat rotavirus
oral rehydration therapy
What is caused by campylobacter ‘curved bacteria’
food poisoning
transmission through undercooked meat/ unpasteurised milk/ untreated water
- treat with erythromycin
what is caused by e.coli
diverse group of gram-neg bacteria (most harmless)
6 pathotypes cause diarrhoea
which type of e.coli causes kidney damage
Shiga toxin-producing E. coli (STEC)
how does C. Diff. cause disease
Taking antibiotics causes dysbiosis
C. Diff. leads to inflammation + disease due to disturbance of gut microbiota
