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

Name a superbug.

Answer 4

Clostridium difficile

Question 5

What is the treatment for C. difficile?

Answer 5

Metronidazole and Vancomycin Isolate patient Stop current antibiotics Faecal Microbiota Transplantation

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

• Mucus layer - Goblet cells
• Epithelial monolayer - Tight junctions
• Paneth Cells (small intestine)
• Bases of crypts of Lieberkühn.
• Secrete Antimicrobial peptides (defensins) and lysozyme.

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

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

Where and in which layer of the gut wall are Peyer’s patches found?

Answer 11

Distal Ileum

Lamina Propria

Question 12

Where do activated T and B cells go to proliferate?

Answer 12

Superior Mesenteric Lymph Nodes

Question 13

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

Answer 13

Intraepithelial lymphocytes

Question 14

What is the difference between conventional and unconventional T cells?

Answer 14

Conventional - migrate from other tissues Unconventional - resident

Question 15

What other innate cells are involved?

Answer 15

NK cells

Question 16

What three signals determine the T cell response?

Answer 16

Presentation of antigen on MHC Costimulation Cytokines

Question 17

What are the mechanisms of immune tolerance?

Answer 17

Anergy Deletion Regulation (Tregs)

Question 18

What is Crohn’s disease?

Answer 18

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

Question 19

Name 4 structures where GALT is ORGANISED

Answer 19

1. Caecal Patches (large intestine)
2. Peyer’s Patches (small intestine)
3. Isolated lymphoid follicles
4. Mesenteric lymphoid follicles (encapsulated)

Question 20

Name 2 places where GALT isn’t organised

Answer 20

• Intra-epithelial lymphocytes – Make up one-fifth of intestinal epithelium, e.g., T cells, NK cells
• Lamina propria lymphocytes

Question 21

What are the Roles of M Cells?

Answer 21

• Antigen uptake via M (microfold) cells within FAE.
• M cells express IgA receptors, facilitating transfer of IgA-bacteria complex into the peyer’s patches.

Question 22

What’s the role of Secretory IgA?

Answer 22

sIgA binds luminal antigen, thereby preventing its adhesion and consequent invasion.

Question 23

What’s the mechanism of IBS?

Answer 23

1. Visceral Hypertension
2. Triggered by diet / stress

Question 24

What are the symptoms of IBS?

Answer 24

1. Recurrent abdominal pain
2. Abnormal Bowel motility
3. Constripation and/or Diarrhoea

Question 25

How to treat IBS?

Answer 25

1. Diet modification - Avoiding certain foods such as apples, beans, cauliflowers.
2. Treatment of constipation - soluble fiber, stool softeners and osmotic laxatives.
3. Treatment of spasms and pain - anti-diarrheals, anti-muscarinic.
4. Management of stress, anxiety, depression.

Question 26

What is coeliac disease in terms of its mechanisms, symptoms, diagnosis and treatment?

Answer 26

Question 27

Compare Crohn’s disease and Ulcerative Colitis

Answer 27