12.10 Immunology: Normal microbiota 1 Flashcards
Where are the majority of the bacteria?
Distal colon
Where are anaerobes rare?
Stomach (pH)
What are the majority of commensal species?
4 main phyla
firmicutes, bacteroidetes, actinobacteria, proteobacteria
What type of commensals are associated with vaginal delivery?
Firmicutes, bifidobacteria
What is the composition of the microbiota like within a host?
Stable (influenced), each site has a high level of diversity
What happens when mice are fed an iron free diet?
Increase in Bifidobacteria/Clostridia
Decrease in bacteroides
What happen in germ free mice? How?
Need higher energy intake
microbiota supply nutrients or alter metabolic machinery
What do microbiota have to do with metabolic pathways?
Provide important pathways (site composition varies but pathways are similar)
What do microbiota produce?
Short chain fatty acids from undigestible carbohydrates (maintain enterocyte differentiation)
Why does colonic fermentation of dietary fibres occur?
Energy for colon and liver, also control of gene expression
What is the mucosal immune system? What does it contain?
Part of MALT
Largest collection of lymphoid tissue (SI: 400m2)
What does immune activation in the gut lead to?
Protection from pathogens (IgA)
Tolerance to normal microbiota/food antigens
Where are isolated lymphoid follicles?
Large and small intestine
collection of T and B cells
Where are Peyers patches?
Small intestine
What do enterocytes do? Where are they?
Secrete TGF-B, CKs, ChKs and anti-microbial peptides
Top of villus
What do Goblet cells do? Where are they?
Secrete mucin, lysozyme, lactoferrin
On villi
Where are the effector cells located? (in the villus)
Lamina propria lymphocytes
Where are Paneth cells? What do they do?
Bottom of crypts, secrete defensins
What cells have critical roles in inducing tolerance?
Enterocytes
IEL (incl. innate LCs)
What cells are enterocytes?
Goblet, Paneth cells
What are the mechanisms for controlleeed antigen access?
M cells, dendritic cells
What does IL-22 do?
What produces it?
Enhances microbial defence, epithelial repair and barrier integrity
NK or IELs
What do MAIT cells do?
Respond rapidly to bacterial antigens
mucosal associated invariant T cells
Where are M cells? How do they sample lumen?
Over lymphoid aggregates
Lack a thick glycocalyx, don’t secrete mucous for easier access
What do the DCs in the mucosa do? (4)
Sample antigen
Induce T-cell differentiation
Bias B cell–>IgA
Induce mucosal adressin (a4B7, homing signal and binds MAdCAM1)
