gut as an immune organ

Question 1

what is the surface area of the skin?

Answer 1

25m2

Question 2

what is the surface area of the mucosae?

Answer 2

32m2

Question 3

why does the mucosae have such a large surface area?

Answer 3

due to its length and the presence of villi and microvilli

Question 4

what lines the gut and what is its function?

Answer 4

a layer of epithelium

selective barrier of absorption

Question 5

name organisms which cause infections of the gut or which enter the body through the gut

Answer 5

Vibrio cholera
Helicobacter pylori
Salmonella enteritidis
Giardia lamblia
Clostridium difficile
Worms

Question 6

what immune cells are normally found in the small intestine?

Answer 6

T cells

IgA plasma cells

Question 7

what are the two T cell markers?

Answer 7

CD4 and CD8

Question 8

what is cluster of differentiation?

Answer 8

an immunohistochemistry technique used to identify and investigate cell surface molecules in T cells

Question 9

what does the CD4/CD8 ratio show and what should it normally be?

Answer 9

immune system health

between 1 and 4

Question 10

what are Peyer’s patches?

Answer 10

organised lymphoid follicles

Question 11

where are Peyer’s patches found?

Answer 11

small intestine

Question 12

what cells are Peyer’s patches rich in?

Answer 12

T cells

Question 13

what are M cells?

Answer 13

specialised epithelial cells of the GALT and MALT which sit on top of PPs

Question 14

what do M cells do?

Answer 14

sample the antigens of the gut lumen

transport antigens from lumen across the epithelium to APCs

Question 15

what are the main type of APCs in the gut?

Answer 15

dendritic cells

Question 16

how can dendritic cells sample the gut content?

Answer 16

directly

via the peyer’s patch

Question 17

which vitamin is retinol?

Answer 17

vitamin A

Question 18

which enzyme is needed to convert retinol to retinoic acid?

Answer 18

retinal dehydrogenase from gut dendritic cells

Question 19

explain how b and T cells gain gut homing capacity

Answer 19

retinoic acid binds to T cell DNA

activates transcription of CCR9 and a4b7

Question 20

what are enterocytes?

Answer 20

intestinal epithelial cells

Question 21

how do gut homing cells know to home to the gut mucosa?

Answer 21

only enterocytes express CCL25 and MadCAM - ligands interact with gut homing T cell receptors to stop them from circulating

Question 22

what is the ligand for the CCR9 receptor and what type of molecule is it?

Answer 22

CCL25

chemokine

Question 23

what is a chemokine?

Answer 23

a molecule which makes cells move

Question 24

what is the ligand for the a4b7 receptor?

Answer 24

MadCAM

Question 25

what is the main immunoglobulin in lymphoid organs?

Answer 25

IgG

Question 26

what are the main immunoglobulins in the mucosa?

Answer 26

IgM and IgA

Question 27

how many amino acids in the constant region of IgA and IgM?

Answer 27

18

Question 28

why is a cysteine residue needed in IgM and IgA?

Answer 28

polymerisation

Question 29

what do J chains do?

Answer 29

act as the glue between two Fc regions in an antibody

Question 30

what shape is IgA in mucous secretions?

Answer 30

dimer

Question 31

what shape is IgA in the plasma?

Answer 31

monomer

Question 32

what shape is IgM in mucous secretions?

Answer 32

pentamer

Question 33

what shape is IgM in the plasma?

Answer 33

pentamer

Question 34

how is IgA actively transported across the epithelium into the gut lumen?

Answer 34

polymeric Ig receptor

Question 35

what does SIgA protect against?

Answer 35

enteric toxins and pathogenic microorganisms

Question 36

through what methods does SIgA clear antigens and pathogens from the intestinal lumen?

Answer 36

blocking access to epithelial receptors trapping them in mucus facilitating their removal by peristaltic and mucociliary activities

Question 37

which immunoglobulin can you live without?

Answer 37

IgA

Question 38

what percentage of people with coeliac disease have IgA deficiency?

Answer 38

2%

Question 39

summarise how the immune system deals with viruses and bacteria in the gut

Answer 39

1. The gut immune system has to know what antigens are in the gut 2. Peyer’s patch M cells sample antigen 3. T and B cells activated in PP migrate to the mucosa 4. IgA is actively transported across the epithelium by the polyIg receptor 5. In the lumen IgA agglutinates viruses and bacteria

Question 40

what ligand do the breast epithelium and endothelium express?

Answer 40

endothelium - MadCAM | epithelium - CCL25

Question 41

which immunoglobulin are babies totally deficient in?

Answer 41

IgA

Question 42

wha is coeliac disease?

Answer 42

an autoimmune disease of the small intestine