Commensal Microbiota and the Immune System Flashcards
Describe four roles of commensal microbiota
1) Required for development of the immune system
2) Provide energy by metabolizing dietary polysaccharides
3) Provide vitamins
4) Protect from pathogenic bacteria
Describe the composition of commensal microbiota throughout the body.
Commensal bacteria are present at all mucosal surfaces and the composition is different at different sites
How do we know that intestinal bacteria are responsible for development of the immune system?
Germfree animals have almost no secondary lymphoid tissues, including mucosal tissues
Describe how commensal bacteria provides protection from infections disease agents
The colon is healthy when colonized by large numbers of commensal bacteria. When they are killed off by antibiotics, clostridium difficile gains a foothold and produces toxins that cause mucosal injury
This is true for E. coli as well
In general, commensal bacteria prevent the colonization of the GI tract by harmful bacteria
How do commensals balance pro and anti-inflammatory immune reactions
Some bacteria induce an inflammatory response while others induce anti-inflammatory responses
What is dysbiosis? What type of immune responses is driven by dysbiosis?
Microbial imbalance
Dysbiosis can favor pro-inflammatory responses
How does dysbiosis affect immune responses in the gut?
Changes in commensals can tip the balance between inflammatory (Th1 and Th17) and anti-inflammatory (Treg) responses in the intestines.
How can intestinal microbes protect from allergy?
Commensals regulate the balance between Th1 and Th2 responses
Bacteria and viruses elicit Th1 responses (IL-2 and IFNgamma); Th1 responses downregulate Th2 responses (IgE-allergy); insufficient Th1 response due to decreased bacterial and viral load would increase Th2 responses (IgE)
Can intestinal bacteria protect against autoimmunity?
Yes- through induction of anti-inflammatory Treg cells
What is the connection between TLR5 and obesity?
Mice lacking TLR5 (recognizes flagella of bacteria) are obese
Fecal transplant from obese TLR5 KO mice to antibiotic-treated WT resulted in obese mice.
This shows that the microbiota can cause obesity
Can diet induce changes in the microbiota that can promote obesity?
Yes.
High fat diet affects innate lymphoid cells to secrete IL-22 which induces expression of anti-microbial peptides which alter microbiota.
Name 4 causes of dysbiosis
Antibiotics
Diet
Early childhood experiences
Cecarean delivery
Can gut microbiota altera cancer therapies?
Yes
