Immunological Mechanisms and Infections of the GIT

Question 1

State three infections of the GIT.

Answer 1

Oral candidiasis
Helicobacter pylori
Traveller’s Diarrhoea

Question 2

What does H. pylori cause?

Answer 2

Increased acid secretion

Question 3

State three causes of Traveller’s Diarrhoea.

Answer 3

Escherichia coli
Salmonella
Shigella

Question 4

What does Clostridium difficile do?

Answer 4

It takes advantage of antibiotics killing many commensal bacteria - it gains a foothold and then produces toxins to cause mucosal injury.

Treatment may involve FAECAL MICROBIOTA TRANSPLANTATION.

Question 5

What is the treatment for C. difficile?

Answer 5

Metronidazole and Vancomycin

Question 6

What components make up mucosal defence?

Answer 6

Anatomical and chemical barriers
Commensal bacteria
GALT and MALT

Question 7

What makes up the epithelial barrier?

Answer 7

Goblet cells, Paneth cells, antimicrobial peptides, secretory IgA, tight junctions

Question 8

What is GALT and what does it do?

Answer 8

Collections of T and B cells which generate lymphoid cells and antibodies
Produces secretory and interstitial IgA, IgM, IgG and cell mediated immunity

Question 9

What do Peyer’s Patches consist of?

Answer 9

Naïve T and B cells

Sub-epithelial dome above the Peyer’s patch which contains dendritic cells

Question 10

How is the epithelium above Peyer’s patches different to normal gut epithelia?

Answer 10

It is Follicle Associated Epithelium (FAE) - there are no goblet cells, no microvilli and no secretory IgA

Question 11

In which layer of the gut wall are Peyer’s patches found?

Answer 11

Lamina Propria

Question 12

Where do activated T and B cells go to proliferate?

Answer 12

Superior Mesenteric Lymph Nodes

Question 13

What is the role of secretory IgA?

Answer 13

Prevent attachment and entry of pathogens

Question 14

What immune cell makes up 1/5 of intestinal epithelium?

Answer 14

Intraepithelial lymphocytes

Question 15

What is the difference between conventional and unconventional T cells?

Answer 15

Conventional - migrate from other tissues

Unconventional - resident, express unusual combinations of CD4, CD8 and gamma delta receptor

Question 16

What other innate cells are involved?

Answer 16

NK cells

Question 17

What three signals determine the T cell response?

Answer 17

Presentation of antigen on MHC
Costimulation
Cytokines

Question 18

What are the mechanisms of immune tolerance?

Answer 18

Anergy
Deletion
Regulation (Tregs)

Question 19

What is Crohn’s disease?

Answer 19

Inflammatory thickening of the bowel wall - leads to ulceration, diarrhoea and pain

Question 20

Name 4 structures where GALT is ORGANISED

Answer 20

Caecal patches/Cryptopatches
Peyer’s Patches
Isolated lymphoid follicles
Mesenteric lymphoid follicles

Question 21

Name 2 places where GALT isn’t organised

Answer 21

Intra-epithelial lymphocytes

Lamina propria lymphocytes

Question 22

What can happen to healthy microbiota to make it negatively affect the body?

Answer 22

DYSBIOSIS

Question 23

Gut homing?

Answer 23

Lymphocytes selectively home to sites similar to initial priming.
Antigen presentation in GALT favours gut homing characteristics - specific integrins and chemokine receptors e.g. alpha 4 beta 7 integrin/MAdCAM-1 adhesion

Question 24

Causes of gastroenteritis/infectious diarrhoea?

Answer 24

Virus = Rotavirus, Norovirus
Bacteria = Campylobacter jejuni, Esterichia coli, Salmonella, Shigella, Clostridium difficile
Protozoal parasitic = Giardia lamblia, Entamoeba histolytica

Question 25

Coeliac Disease

Answer 25

Autoimmune disease during response to gluten, damage is reversible.

Question 26

Irritable bowel syndrome

Answer 26

Visceral hypersensitivity which is triggered by diet and stress - it is a function disorder which causes little damage.

Question 27

Inflammatory bowel disease

Answer 27

Aberrant inflammatory responses to microbiota which can cause serious damage to the GI tract - may require surgery.

2 forms:
Ulcerative colitis (restricted to colon, damage to mucosa and submucosa)
Crohn's disease (anywhere in GI tract, entire intestinal wall may be affected all the way to the serosa, surgery is not curative)