Immunology of the gut Flashcards
What kind of environment is the epithelium of the digestive tract?
External environment because bacteria can reach it without crossing a membrane
What are the 4 mechanisms of defence of GI mucosa?
- Physical barriers
- Chemical barriers (bactericidal enzymes from Paneth cells)
- Bacteria protection
- Immunological
Lymphocytes in the lamina propria do what?
B-cells secreting IgA mainly
What are Peyers patches covered in?
covered in follicle associated epithelium (FAE)
What are Peyers patches rich in?
B cells
T cells
Macrophages
Dendritic cells
Where are M cells found and what is their main function?
Found on FAE.
Main function = perform transcytosis of luminal bacteria/antigens/proteins
M cells express IgA receptors
What does the apical membrane of the M cell have?
Microfold
Why is the basolateral membrane of M cells invaginated?
To reduce intracellular distance that antigens have to travel
How is the apical membrane of the M cell specialised for uptake and transport of antigens?
- Reduced glycocalyx
2. Lack of hydrolytic enzymes
How are large bacteria and particles transported?
By phagocytosis
M cells produce?
IL-1
Cells of the villus side of the crypt develop into?
What about cells in the FAE side of the crypt?
Villus - enteroendocrine cells, enterocytes, goblet cells
FAE side - enterocytes, M cells, rarely goblet cells. Has low number of enterocytes and goblet cells
What lies beneath the FAE?
Sub epithelial dome.
Contains DCs, naive B cells, CD4, CD8, macrophages
Particles transported by M cells can be captured by dendritic cells, which then maturate after migrating to B cell follicles.
Why is an M cell an ideal entry point for pathogens?
Accessibility and ability to transcytose
How is secretory IgA produced?
- Plasma cells secrete IgA dimer bound by a J chain, into interstitial space
- IgA dimer binds to receptor on basolateral membrane of enterocytes.
- Receptor becomes the secretory part of IgA and binds to the dimer. SIgA formed.
- SIgA endocytose and then actively transported to apical membrane.
- Exocytosed into gut lumen.