Gastro - Gut immunology

Question 1

What is a symbiont?

Answer 1

Organisms that live with a host without any benefit or harm to either one

Question 2

What is a commensal organism?

Answer 2

Organisms that live with a host which benefit from it but do not harm the host

Question 3

What is a pathobiont?

Answer 3

Organisms that under certain conditions have the potential to cause dysregulated inflammation and disease

Question 4

What is dysbiosis?

Answer 4

An altered microbiota composition

Question 5

What is MALT?

Answer 5

Mucosa associated lymphoid tissue:

• Found in the submucosa below the epithelum, as lymphoid mass containing lymphoid follicles

Question 6

What is GALT?

Answer 6

Gut associated lymphoid tissue:

• Responsible for both adaptive & innate immune responses
• Consists of B&T lymphocytes, macrophages, APC, and specific epithelial & intra-epithelial lymphocytes

Question 7

What are Peyer’s patches?

Answer 7

Aggregated lymphoid follicles covered with follicle associated epithelium
They work with the immune system to prevent pathogens from entering the body during digestion

Question 8

What is special about folicle associated epithelium?

Answer 8

• No globlet cells
• No secretory IgA
• No microvilli

Question 9

What are M (microfold) cells?

Answer 9

• They are antigen up taking cells within the follicle associated epithelium
• They express IgA receptors, which help in the transfer of IgA-bacteria complex to the Peyer’s patches below

Question 10

What is antigen sampling by trans-epithelial dendritic cells?

Answer 10

Some dendritic cells underneath the mucosal epithelium can open up tight junction proteins between epithelial cells and squeeze dendrites through and sample bacteria and bring it back through the dendrite in the gap

Question 11

How does the B cell adaptive response occur?

Answer 11

• Mature naive B cells express IgM in Peyer’s patches
• On antigen presentation the class switches to IgA
• T-cells and epithelial cells influence the B-cell maturation via cytokine production
• B-cells further mature to become IgA secreting plasma cells

Question 12

How do lymphocytes migrate?

Answer 12

• The lymphocyte rolls in the high endothelial venule
• The cell then becomes activated when it binds to the MAdCAM1 receptor
• The lymphocyte then goes through arrest where it squeezes into the lamina propria

Question 13

Explain the mechanism of cholera

Answer 13

• Cholera enters the body and when it reaches the small intestine it comes into contact with epithelium and releases cholera enterotoxin
• This enterotoxin increases the activity of adenylase cyclase with increase the amount of cAMP
• This results in active secretion of salts into the the intestine
• This leads to water following and increasing water loss through faeces, causing diarrhoea

Question 14

What are the viral causes of infectious diarrhoea?

Answer 14

• Rotavirus (children)

- Norovirus