gut as an immune organ Flashcards
what is the surface area of the skin?
25m2
what is the surface area of the mucosae?
32m2
why does the mucosae have such a large surface area?
due to its length and the presence of villi and microvilli
what lines the gut and what is its function?
a layer of epithelium
selective barrier of absorption
name organisms which cause infections of the gut or which enter the body through the gut
Vibrio cholera Helicobacter pylori Salmonella enteritidis Giardia lamblia Clostridium difficile Worms
what immune cells are normally found in the small intestine?
T cells
IgA plasma cells
what are the two T cell markers?
CD4 and CD8
what is cluster of differentiation?
an immunohistochemistry technique used to identify and investigate cell surface molecules in T cells
what does the CD4/CD8 ratio show and what should it normally be?
immune system health
between 1 and 4
what are Peyer’s patches?
organised lymphoid follicles
where are Peyer’s patches found?
small intestine
what cells are Peyer’s patches rich in?
T cells
what are M cells?
specialised epithelial cells of the GALT and MALT which sit on top of PPs
what do M cells do?
sample the antigens of the gut lumen
transport antigens from lumen across the epithelium to APCs
what are the main type of APCs in the gut?
dendritic cells
how can dendritic cells sample the gut content?
directly
via the peyer’s patch
which vitamin is retinol?
vitamin A
which enzyme is needed to convert retinol to retinoic acid?
retinal dehydrogenase from gut dendritic cells
explain how b and T cells gain gut homing capacity
retinoic acid binds to T cell DNA
activates transcription of CCR9 and a4b7
what are enterocytes?
intestinal epithelial cells
how do gut homing cells know to home to the gut mucosa?
only enterocytes express CCL25 and MadCAM - ligands interact with gut homing T cell receptors to stop them from circulating
what is the ligand for the CCR9 receptor and what type of molecule is it?
CCL25
chemokine
what is a chemokine?
a molecule which makes cells move
what is the ligand for the a4b7 receptor?
MadCAM
what is the main immunoglobulin in lymphoid organs?
IgG
what are the main immunoglobulins in the mucosa?
IgM and IgA
how many amino acids in the constant region of IgA and IgM?
18
why is a cysteine residue needed in IgM and IgA?
polymerisation
what do J chains do?
act as the glue between two Fc regions in an antibody
what shape is IgA in mucous secretions?
dimer
what shape is IgA in the plasma?
monomer
what shape is IgM in mucous secretions?
pentamer
what shape is IgM in the plasma?
pentamer
how is IgA actively transported across the epithelium into the gut lumen?
polymeric Ig receptor
what does SIgA protect against?
enteric toxins and pathogenic microorganisms
through what methods does SIgA clear antigens and pathogens from the intestinal lumen?
blocking access to epithelial receptors
trapping them in mucus
facilitating their removal by peristaltic and mucociliary activities
which immunoglobulin can you live without?
IgA
what percentage of people with coeliac disease have IgA deficiency?
2%
summarise how the immune system deals with viruses and bacteria in the gut
- The gut immune system has to know what antigens are in the gut
- Peyer’s patch M cells sample antigen
- T and B cells activated in PP migrate to the mucosa
- IgA is actively transported across the epithelium by the polyIg receptor
- In the lumen IgA agglutinates viruses and bacteria
what ligand do the breast epithelium and endothelium express?
endothelium - MadCAM
epithelium - CCL25
which immunoglobulin are babies totally deficient in?
IgA
wha is coeliac disease?
an autoimmune disease of the small intestine
