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Gastrointestinal > Mucosal immunology of the GI tract > Flashcards

Mucosal immunology of the GI tract Flashcards

1
Q

What is the physiological function of the GI tract?

A

Food digestion and absorption

Immune regulation

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2
Q

Describe the cellular structure of the small intestine

A

Villi and crypts

Goblet cells, paneth cells and Peyer’s patches

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3
Q

Describe the cellular structure of the epithelium of the large intestine?

A 
Crypts, no villi
No paneth cells 
Lots of goblet cells and mucus 
No Peyer's patches
Enterocyctes do defence
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4
Q

What does the mucosal immune system of the GI tract have to do?

A

Capture the antigen
Initiate the local immune response
Carryout effector functions to clear any infection

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5
Q

Where does antigen capture occur?

A

In Peyer’s patches and directly across the epithelium by dendritic cells

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6
Q

What are the specialized epithelial cells in Peyer’s patched called?

A

M cells

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7
Q

What happens to antigens when they meet M cells?

A

M cells take up the antigen by endocytosis and phagocytosis
Antigen is transported across the M cells in the vesicles and released at the basal surface
Antigen is bound by dendritic cells, which activate T cell

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8
Q

Where does initiation of the intestinal immune response occur?

A

In the mesenteric lymph nodes

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9
Q

What are lymph nodes a hub for?

A

Maximising T lymphocyte exposure to antigens

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10
Q

What two types of cell drain to the lymph nodes with antigens?

A

Dendritic cells and B cells

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11
Q

What happens to T lymphcytes when they are activated?

A

The loose CCR7 meaning they can no longer re-circulate

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12
Q

Where do activated T cells drain to?

A

They drain via the mesenteric lymph nodes to the thoracic duct and return to the gut via the bloodstream

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13
Q

What is the most important antibody in the gut/

A

IgA (80% of immunoglobin in the gut)

IgM 15% and IgG 5%

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14
Q

How is IgA produced and released?

A

Produced by a IgA-secreting cell
Binds to receptor on basolateral face of epithelial cell
Endocytosis
Transcytosis to apical face of epithelial cell
Release of IgA dimer at apical face of epithelial cell

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15
Q

What does secreted IgA do?

A

Secreted IgA binds to pathogens and toxins and neutralizes them
While being secreted, IgA can bind to toxins that have entered epithelial cells and export them

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16
Q

What are intraepithelial lymphocytes?

A

Cells that sit within the epithelial barrier

90% are T cells, 80% of which are CD8+ (effector T cells) that do not need activated

17
Q

What are the two recognition mechanisms for intraepithelial lymphocytes?

A

Virus specific recognition (TCR/CD8 cells)

Stress specific recognition (NK cells)

18
Q

What is the default state of the gut immune system?

A

Systemic hyporesponsiveness

19
Q

What immunoglobin causes an aggressive response?

A

IgE

20
Q

What are the distinctive anatomical features of the mucosal immune system?

A

The tissues sit in a very intimate relationship between mucosal epithelial and lymphoid tissue
There are organised lymphoid structures unique to mucosal sites
Specialized antigen uptake mechanisms

21
Q

What is the hygiene hypothesis?

A

A theory that suggests a young child’s environment can be “too clean” to effectively stimulate or challenge the child’s immune system to respond to various threats during the time their immune system is maturing

22
Q

What mechanism eliminates most intestinal infections?

A

Innate mechanisms

23
Q

What are the innate receptors?

A

Pattern recognition receptors (PRR)

24
Q

What happens when pattern recognition receptors are activated?

A

Gene transcription and production of cytokines, chemokines and defensins

25
Q

What is coeliac disease?

A

Damage to the small intestine due to an abnormal reaction to the gluten antigen
It has a T cell component
Results in malnutirion
(not an allergy)

26
Q

What is the score to measure the scale of coeliac disease?

A

MARSH score

27
Q

How does the antigen cause villi destruction?

A

The gluten peptides activate mucosal epithelial cells to express MIC molecules
Intraepithelial lymphocytes are activated by MIC molecules binding to the expressed NKG2D
They kill the epithelial cells by programmed cells death through the recognition of the stress receptor

28
Q

What is a second killing mechanism in coelic disease?

A

Enzyme modifies peptides so they can bind to MHC class II molecules
Bound peptide activates gluten-specific CD4-T cells
Activated T cells kill mucosal epithelial cells

29
Q

How is coeliac disease diagnosed?

A

Serology and genetics in most children

30
Q

What other tests are down when diagnosis coeliac disease to avoid a false negative?

A

IgA deficiency tests

also if they are have IgA deficiency they go for biopsy as 10x more likely to have the disease

31
Q

What is inflammatory bowel disease?

A

Altered function and imbalance of the relationship between prevention of invasion by pathogens and tolerance to innocuous foods and commensal microorganisms

32
Q

What are the two subtypes of inflammatory bowel disease?

A

Crohn’s and ulcerative colitis.

33
Q

Which inflammatory bowel disease has the deepest inflammation?

A

Crohn’s disesae

34
Q

Which inflammatory bowel disease has the greatest genetic influence?

A

Crohn’s disease

35
Q

Where does Crohn’s disease affect?

A

Any part of the GI tract, commonly the distal ileum and colon

36
Q

Where does ulcerative colitis affect?

A

Restricted to the rectum and colon

37
Q

What is the difference between CD and UC?

A

In CD there are healthy parts of the intestine mixed in between inflammed areas
In UC it is continuous inflammation of the colon
UC only occurs in the inner most lining of the colon whereas CD can occur in all the layers of the bowel walls

38
Q

What is the treatment for inflammatory bowel disease?

A

Non-specific anti-inflammatory and immunosuppresive drugs

39
Q

What causes a food allergy?

A

Type I hypersensitivity reaction initiated by crosslinking of allergen specific IgE on the surface of mast cells with the specific allergen

Gastrointestinal (11 decks)

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