Gut Immunology

Question 1

What does microbiota mean?

Answer 1

A mixture of microorganisms that makes up a community within an anatomical niche

Question 2

What does microbiome mean?

Answer 2

Collective genomes of all microbiota in all the different anatomical niches

Question 3

What host factors stimulate bacterial growth?

Answer 3

• Ingested nutrients
• Secreted nutrients

Question 4

What host factors inhibit bacterial growth?

Answer 4

• Chemical digestive factors → bacterial lysis
• Peristalsis, contractions, defecation → bacterial elimination

Question 5

Define dysbiosis

Answer 5

Altered microbiota composition.

Question 6

What are symbionts in regards to immunology?

Answer 6

Microbiota and humans live with each other but not with benefit or harm to either, they just live

Question 7

What are commensals in regards to immunology?

Answer 7

microorganisms that benefits from associating with host but has no effect on the host

Question 8

What are pathobionts in regards to immunology?

Answer 8

Symbionts that doesn’t normally elicit inflammatory response, but under specific conditions can cause dysregulated inflammatory disease.

Question 9

What causes either equilibrium or dysbiosis (depending on how it is)?

Answer 9

• Infection or inflammation
• Diet
• Xenobiotics
• Hygiene
• Genetics

Question 10

How can dysbiosis negatively affect the rest of the body?

Answer 10

Through producing bacterial metabolites and toxins

Question 11

Give 4 examples of bacterial metabolites and toxins

Answer 11

• TMAO: increases cholesterol deposition in artery walls to cause atherosclerosis

-4-EPS: associated with autism

• SCFA’s: short chain fatty acids, decreased numbers are associated with IBD and increased numbers are associated with neuropsychiatric disorders e.g. stress
• AHR ligands, associated with:
  • MS
  • rheumatoid arthritis
  • asthma

Question 12

What is the first line of defence the body has against pathogens?

Answer 12

Mucosal defence

Question 13

What are the 3 layers of mucosal defence?

Answer 13

1st- Physical barriers
2nd-Commensal bacteria
3rd- Immunological

Question 14

What 2 components make up the physical barriers of mucosal defence.

Answer 14

-Anatomical barriers
-Chemical barriers

Question 15

What is the epithelial barrier of the mucosal defence made up of?

Answer 15

-Mucous layer, made by goblet cells
-Epithelial monolayer with tight junctions
-Paneth cells found in bases of crypts of Lieberkuhn
- Secrete antimicrobial
peptides (defensins) and
lysozyme

Question 16

What are the two types of lymphoid tissue in mucosal defence?

Answer 16

-MALT (Mucosa Associated Lymphoid Tissue)
-GALT (Gut Associated Lymphoid Tissue)

Question 17

Where are Mucosa Associated Lymphoid tissues found and where in the body are they particularly concentrated?

Answer 17

-In submucosa below epithelium, concentrated in the oral cavity-pharyngeal palatine…

Question 18

How big is the GALT?

Answer 18

Largest mass of lymphoid tissue in the body.

Question 19

What types of immune response is the GALT responsible for?

Answer 19

Both adaptive and innate immune response

Question 20

What two types of GALT are there?

Answer 20

-Non organized
-Organized

Question 21

What are peyers patches also known as?

Answer 21

Immune sensors

Question 22

What are peyer’s patches associated with?

Answer 22

Follicle associated epithelium. (FAE)

Question 23

What is special about the structure of FAE (follicle associated epithelium).

Answer 23

No goblet cells, no secretory IgA, no microvilli.

Question 24

What kind cells do peyers patches contain?

Answer 24

Organised collection of Naive T & B cells.

Question 25

What cells within the FAE uptake antigens?

Answer 25

M(microfold) cells

Question 26

What kind of receptors do M cells express and what does this facilitate?

Answer 26

IgA receptors,
facilitates the transfer of IgA-bacteria complex into the Peyer’s patches.

Question 27

Apart from M cells what is the alternative route of bacterial invasion in the gut?

Answer 27

Dendritic cells can directly sample bacteria through tight junctions and transport them back to lymph nodes.

Question 28

How are Dendritic cells able to maintain the integrity of the epithelium barrier once they’ve sampled antigens through the tight junction?

Answer 28

They express tight junction protein, such as occludin and claudin 1.

Question 29

What do mature naïve B-cells express in Peyer’s patches and what does this switch to on antigen presentation?

Answer 29

Express IgM in Peyers patch, class switches to IgA.

Question 30

What do T cells and epithelial cells influence B cell maturation via?

Answer 30

Cytokine production

Question 31

What is the lamina propria?

Answer 31

layer beneath epithelial layer.

Question 32

What do activated B cells further mature into?

Answer 32

IgA secreting plasma cells.

Question 33

What is the main lymphatic vessel for return of lymph from GI to venous system?

Answer 33

Thoracic duct

Question 34

Where do lymphocytes go to undergo proliferation?

Answer 34

Mesenteric lymph nodes

Question 35

How does the cholera enterotoxin get internalised?

Answer 35

Retrograde endocytosis

Question 36

What does the cholera enterotoxin lead to.

Answer 36

Increased cAMP levels which increases active secretion of salts (Na+, K+, Cl-, HCO3-) leading to diarrhoea. (Water folllows)

Question 37

What is the gold standard for cholera diagnosis?

Answer 37

Bacterial culture from stool sample on selective agar

Question 38

What is the most common cause of food poisoning in the UK?

Answer 38

Campylobacter