Immuno Flashcards
What is the human microbiota?
a. Provide extra source of genes
b. Co-evolution → provides diverse physiological properties we have not had to evolve on our own = mutualist
c. 99.9% anaerobic (from stomach onwards; rare to grow in the stomach) → minute proportion aerobes
d. NB. Less than 30% are culturable
Why study the microbiome?
Data suggests that the microbiome is intimately associated with health and disease
What sort of bacteria do we find in the gut, throat, skin and vaginal canal?
Gut is dominated by gram negative
Skin and throat = gram positive
Vaginal = mainly gram positive
Number and species of bacteria vary greatly
What are the main phyla of the microbiota?
i. Bacteriodetes
ii. Firmicutes
iii. Actinobacteria
iv. Proteobacteria (eg. E. coli)
The relative concentration shift in different regions of the body
Where are most of the bacteria in the GIT found?
In the LI
What is the role of the microbiota?
Genes of the microbiota contribute to:
Metabolism
Immune protection
What phenomenon is observed in animals grown in a germ free environment?
Require more energy to function.
Indicates that microbiota must confer some mutualistic benefit
What are some factors which influence the gut microbiota?
Age - diversity decreases with age
Mode of delivery - i. Vaginal delivery associated with rapid acquisition of Firmicutes, Bifidobacteria
ii. Caesarian birth associated with delayed microbiota development + restricted diversity
Diet - influences diversity and numbers
Antibiotics - short term use can induce long term changes
Genetics and the environment
Chronic inflammation and the production of pro-inflammatory cytokines
What is the role of the microbiota in metabolic activity of the intestine?
(carbohydrates)
Assists in the breakdown of lactose (esp. early in life), cellulose, mucins broken down to SCFAs (10% calories)
What is the role of the microbiota in metabolic activity of the intestine?
(vitamins)
Produces vitamin K, biotin, folate (w/o microbiota problems with production of vitamins)
What is the role of the microbiota in metabolic activity of the intestine?
(bile acids)
Assists in the breakdown of bile acids and the reabosrbiton of its components
What is the role of the microbiota in metabolic activity of the intestine?
(Amino acids)
Assists in the breakdown, especially lysine and threonine; urea → NH3 allows nitrogen recycling to more aa
How do the microbiota alter the metabolic machinery of the host?
Induce changes in host genes involved in CHO + lipid metab. (different phyla have different effects) Bacterial degradation of host glycans (e.g. mucin) elicits synthesis of new glycans by host Induces changes in host genes affecting angiogenesis→ influence supply of O2 and nutrients to tissues. Produce SCFAs (e.g. butyrate) that maintain enterocyte differentiation.
What process occurs in the colon and what are the results?
Complex carbohydrates (such as dietary fibre) are metabolised by the microbiota of the colon to form oligosaccarides and monosaccarides. These are then fermented to short chain fatty acid end products
What are the short chain fatty acids ends products in the colon?
Mainly acetate, proprionate and butyrate
What happens to the short chain fatty acid products of digestion?
They are absorbed by the colon
Butyrate provides energy for colonic epithelial cells
Acetate and proprionate reach the liver and peripheral organs where they acts as substrates for gluconeogenesis and lipogenesis
How to Short chain fatty acids control colonic gene expression?
By inhibiting the enzyme histone deacetlyase (HDAC)
Metabolic regulation through g-protein coupled receptors (GPR41/43)
What are the aggregates of lymphoid cells in the gut called?
Isolated lymphoid follicles (ILFs) - Large and Small intestine
Peyers patches - Small intestine only
These are sites for induction of T and B cell activation
What do goblet cells in the GIT secrete?
Mucins
Lysozyme
Lactoferrin
What do paneth cells secrete?
Defensins
What are the innate defences of the gut?
Peristaltic action Acid Mucous layer Enterocytes Innate leucocytes Mechanism for controlled antigen access
What are the specific roles of enterocytes in the innate defence of the gut?
Barrier - tight epithelial junctions (regular cell turnover)
Antimicrobial factors (bile, lactoferrin, complement)
Cytokines and chemokines
What cells allow controlled antigen access?
M cells
What are the signs of inflammation?
Swelling Heat Loss of function Pain Redness
How is IL-1 formed?
Inactive IL-1B precursor (31kDa) is cleaved to release IL-1B (18kDa)
What is familial cold urticaria?
Inactive IL-1B precursor (31kDa) is cleaved to release IL-1B (18kDa)
What gene is mutated in familial cold urticaria and what family of genes is it from?
- Single nucleotide mutations of a gene called cryopyrin;
* cyropyrin identified as a member of the NOD-like receptor family
Why was the discovery of familial cold urticaria important in the development of our understanding of IL-1?
- Mutations in cryopyrin gene found to be associated with IL-1 converting enzyme (ICE).
- Cryopyrin associated with ICE (interleukin 1 converting enzyme)
- When these patients are cold, the mutation in Cryopyrin some how increased ICE activity and we get increased IL1. (localized inflammatory response).
What is the inflammasome?
The inflammasome is a multiprotein oligomer
The inflammasome is responsible for activation of inflammatory processes
How is the inflammasomes activity regulated?
Excessive inflammasome activity would be very dangerous thus there are two regulatory mechanisms:
- The production of pro-IL-1B and pro-IL-18 is regulated by the presence of certain PAMPs
- The inflammasome complex is only assembled if a second series of PAMPs are present
What is the mechanism of gout?
- Input (consumption) of purines in diet
- Output (excretion) of uric acid (urate).
- Problem in excretion of urate → urate precipitates into crystals → deposit in joints → very painful gout.
What happens after gout forms urate crystals in the joints?
Urate crystals causing; (i) Physical damage (ii) Activating inflammasomes (iii) Macrophages come into joint and remove crystals → macrophages phagocytose crystals but these are too large/chemically difficult to degrade; → crystals activate NLRP3 inflammasome → IL-1B production.
What is alum and when is it used?
Alum causes inflammation and induces an immune response. It is often used in immunisations to encourage an immune response.
What drug is used to treat gout?
Anakinra
When is anakinra absolutely contraindicated?
Neutropenia
What is anakinra?
It is an IL-1 receptor anatagonist