Immunology of the Gut

Question 1

What does the antigen load in the gut consist of?

Answer 1

Resident microbiota
Dietary antigens
Exposure to pathogens

Question 2

What does homeostasis of the gut involve?

Answer 2

Bacterial microbiota

Question 3

What are the 4 major phyla of the gut microbiota?

Answer 3

Bacteroidetes
Firmicutes
Actinobacteria
Proteobacteria

Question 4

Define dysbiosis

Answer 4

Altered microbiota composition

Question 5

What are symbionts?

Answer 5

Microorganisms that live inside us with no effect, they aren’t gaining anything

Question 6

What are commensals?

Answer 6

Microorganism that live in us and benefit from the host but don’t help the host

Question 7

What are pathobionts?

Answer 7

Microorganisms that have potential to cause dysregulated inflammation

Question 8

What affects the immunological equilibrium?

Answer 8

Symbiont, pathobionts and commensals

Question 9

What are the 2 states in the immunological balance?

Answer 9

Regulation and inflammation

Question 10

What are some causes of dysbiosis?

Answer 10

Infection
Inflammation
Diet
Xenobiotics
Hygiene
Genetics

Question 11

Why is dysbiosis significant?

Answer 11

It can have many effects on the rest of the body

Question 12

What are the physical barriers in the mucosal defence?

Answer 12

Epithelial barrier

Peristalsis

Question 13

What are the chemical barriers in the mucosal defence?

Answer 13

Enzymes

Acidic pH

Question 14

What does the epithelial barrier consist of?

Answer 14

Mucus layer - Goblet cells
Epithelial monolayer - tight junctions
Paneth Cells

Question 15

Where are paneth cells found?

Answer 15

Small intestine, bases of crypts of Lieberkühn

Question 16

What do paneth cells secrete?

Answer 16

Antimicrobial peptides (defensins) & lysozyme.

Question 17

Where is mucosa associated lymphoid tissue (MALT) found?

Answer 17

In the submucosa below the epithelium

Question 18

What is the role of gut associated lymphoid tissue (GALT)?

Answer 18

Responsible for both adaptive & innate immune responses

Question 19

What are non organised aspects of GALT?

Answer 19

Intra-epithelial lymphocytes

Lamina propria lymphocytes

Question 20

What are organised aspects of GALT?

Answer 20

Peyer’s patches (small intestine)
Caecal patches (large intestine)
Isolated lymphoid follicles
Mesenteric lymph nodes (encapsulated)

Question 21

Where are Peyer’s patches mostly found?

Answer 21

Submucosa of the small intestine, mainly distal ileum

Question 22

What are the characteristics of follicle associated epithelium (FAE)?

Answer 22

No goblet cells
No secretory IgA
No microvilli

Question 23

What cells are involved in antigen uptake in FAE?

Answer 23

M cells

Question 24

How do M cells in FAE allow antigen/bacteria uptake?

Answer 24

They express IgA receptors, facilitating transfer of IgA-bacteria complex into the Peyer’s patches

Question 25

What do mature naive B cells express in Peyer's patches? What happens after antigen exposure

Answer 25

``` IgM After antigen exposure the class switches to IgA ```

Question 26

What class of antibodies do gut B cells secrete?

Answer 26

IgA

Question 27

What is the role of IgA secreted by gut B cells?

Answer 27

They bind to luminal antigens preventing adhesion and consequent invasion

Question 28

In the gut where does antigen presentation and activation occur?

Answer 28

Peyer's patches

Question 29

How does antigen presentation in Peyer's patches lead to eventual lymphocyte honing and circulation?

Answer 29

After antigen presentation in Peyer's patches they are - transferred to mesenteric lymph nodes where lymphocytes proliferate Lymphocytes then go into circulation via thoracic duct They can then enter the peripheral immune system and go to skin, tonsils etc via honing cascades

Question 30

What is the lifespan of gut enterocytes and goblet cells?

Answer 30

36 hours

Question 31

Why is the lifespan of gut enterocytes and goblet cells so short?

Answer 31

They are the first line of defense against GI pathogens & may be directly affected by toxic substances in diet

Question 32

Whats the mechanism of cholera infection?

Answer 32

Bacteria reaches small intestine and comes into contact with epithelium & releases cholera enterotoxin This leads to eventual loss of Na+, K+, Cl-, Hco3- and water and diarrhoea

Question 33

How is cholera transmitted?

Answer 33

Faecal-oral (via contaminated water and food)

Question 34

What are the main symptoms of cholera?

Answer 34

Severe dehydration & watery diarrhoea

Question 35

How is cholera diagnosed?

Answer 35

Bacterial culture from stool sample

Question 36

How is cholera treated?

Answer 36

Oral rehydration

Question 37

What are some other causes of infectious diarrhoea besides cholera?

Answer 37

Viral (rotavirus/norovirus) Protozoal parasitic Bacterial (E coli, salmonella, shigella, c diff)

Question 38

What type of virus is rotavirus?

Answer 38

RNA

Question 39

Where does rotavirus replicate?

Answer 39

In enterocytes

Question 40

How is infection by rotavirus treated?

Answer 40

Oral rehydration

Question 41

Is there a vaccine for cholera?

Answer 41

Yes

Question 42

Is there a vaccine for rotavirus?

Answer 42

Yes

Question 43

What type of virus is novovirus?

Answer 43

RNA

Question 44

What is the incubation period for novovirus?

Answer 44

24-48 hours

Question 45

What are symptoms of infection by novovirus?

Answer 45

Acute gastroenteritis with recovery in 1 – 3 days

Question 46

How is infection by novovirus treated?

Answer 46

Treatment isn't usually required

Question 47

How is infection by novovirus diagnosed?

Answer 47

Sample PCR

Question 48

Is E coli gram positive or negative?

Answer 48

Negative

Question 49

How may pathotypes of of E coli are associated with diarrhoea?

Answer 49

6

Question 50

How is c diff managed?

Answer 50

Isolate patient (very contagious) Stop current antibiotics Faecal Microbiota Transplantation (FMT) has a 98% cure rate

Question 51

Why is recurrent infection by c diff possible?

Answer 51

Even in intermediate recovery stages it doesn’t produce toxins but it is still invading so you can return to the previous state