8. Infection & Immunology of the Gut Flashcards
What is GALT?
Gut associated lymphoid tissue
The gut must be immunoreactive to?
Pathogens
The gut must have tolerance to?
Food antigns
Commensal bacteria
What is size of the microbiota in the gut?
10^14
What does immune homeostasis and normal healthy immune system require?
Bacterial microbiota
What is the GI Tract constantly in?
A state of restrained activation - tolerance vs. active immune response
How many major phyla of bacteria are there in the gut?
4
What kind of relationship is the one between our microbiota and ourselves?
symbiotic - They can break down certain carbohydrates
How does the number of bacteria change down the GI tract?
They increase - diversity also increases
How can the microbiota be affected?
Infection Diet Xenobiotics (antibiotics) Hygiene Genetics
Define Dysbiosis
An imbalance between the types of organism present in a person’s natural microflora, especially that of the gut, thought to contribute to a range of conditions of ill health.
What defence mechanisms exist in the GUT?
Physical to prevent invasion
Commensal bacteria - occupy ecological niche
Immunological: following invasion - MALT and GALT
What physical defence mechanisms exist?
1) epithelial barrier, peristalsis
2) Chemical (enzymes, pH)
What are the components of the epithelial barrier?
Mucus, epithelial monolayer and paneth cells
How has the epithelial monolayer adapted against disease?
It has tight junctions and transports IgA
How has Panth cells adapted against disease?
Secrete anitmicrobial peptides e.g defensins
Antibacterial lysozyme
Where does MALT tissue exist in the oral cavity?
Tonsils
What do the tonsils contain?
MALT, high endothelial venules: First line of defence against anything inhaled
What are the two types of GALT?
Organised and not organised
Where are not organised GALT distributed?
Through out the tissue - particularly in the lamina propria
Also lots of lymphocytes the epithelial tissue
What are typical structures of organised GALT?
Peyer’s patches - small intestine
Caecal and colonic patches - large intestine
Isolated lymphoid follicles
Mesenteric lymph nodes
How much of the intestinal epithelium does intra-epithelial lymphocytes make?
1/5
What are the different types of intra-epithelial lymphocytes?
Conventional T cells - can migrate form other tissues
Unconventional T cells - resident express CD4, CD8 or gd T cell receptor
Other innate immune cells - NK cells
What are peyer’s patches?
Aggregates of B cell follicles with T cell areas around
What are M cells?
Microfold cells - They sample antigens from the lumen of the gut to present to T and B cells
What is epithelium above Peyer’s patch called?
Follicle Associated Epithelium
Where does the Peyer’s patch drain?
Into lymph nodes
What are TDCs?
Transepithelial dendritic cells which can sample the antigen across the epithelium
Where are most of the Peyer’s patches?
Small intestine - Distal ileum
In Peyer’s patches what do B-cells express?
The mature naive B-cells express IgM
How are B cells in PP activated?
Cytokines
In PP what do B cells express when activated?
IgA
Where do activated B cells secreting IgA go?
Lamina propria - they mature to become IgA secreting plasma cells