Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
77 Cards in this Set
- Front
- Back
|
What is the lamina propria?
|
Supporting tissue for the epithelium
|
|
|
What separates the billions of bacteria in the colon from the sterile tissues?
|
Single layer of mucosa-coated epithelial cells (lamina propria)
|
|
|
How can the body maintain a STATE OF TOLERANCE vs microbiota?
|
Bacteria have LPS (G-) and p/g, which are rec'z by TLRs (LPS) and NOD-LR (p/g) that can trigger an inflammation response if it reaches the epithelium
-Have a mucosal surface on the lumen side of epithelial cells (various in thickness) and keeps bacteria away from the tissues |
|
|
Which cells are involved in the body's state of tolerance?
|
DC cells: can go btw epithelial cells and sample environment of the lumen
M cells: like epithelial cells, but are more permeable to Ag. Deliver Ag to APCs Below M cells, have Peyer's Patch where there are lymphocytes and DC cells. DCs can present the Ag in the lumen to lymphocytes ->these lymphocytes wi ll produce IgA |
|
|
How do the cells in the intestine recognize bacteria?
|
Bacteria have PAMPs (like LPS) which is rec'z by TLRs/NOD-LRs
|
|
|
What can DCs do in the intstine?
|
Can go between cells and sample the environment of the lumen from the tissues (lamina propria)
|
|
|
What are all these mechanisms important for?
|
Important to prevent infection
At the same time, cannot produce inflammtion, otherwise the gut will always be inflammed |
|
|
What is a Peyer's patch?
|
Located in lamina propria part of mucosa in the intestine
Aggregation of organized lymphoid tissue Houses various immune cells such as B and T lymphocytes |
|
|
How is the gut flora maintained in theLUMEN of the small intestine with minimal penetration of mucosal surfaces?
|
Physical barriers
Chemical barriers |
|
|
What are the physical barriers of the intestinal epithelium?
|
Epithelium and tight junctions between epithelial cells
Mucus layer made of mb-bound and secreted mucins (thickness varies, most thick in the lumen, where most of the baceria reside) |
|
|
What are the chemical barriers to the intestinal epithelium?
|
Secretion of antimicrobial peptides (AMPs) (Paneth Cells in small intestine or enterocytes/epitehlial cells in the colon)
Secretion of IgAs Secretion of a C-type lectin (Paneth cells) |
|
|
What is the apical side of the epithelial cells?
|
Faces the lumen
Made of many microvilli Increases SA of lumen Helps absorption of nutrients Has tight junctions to prevent bacteria infiltration from lumen to epithelium |
|
|
What do tight junctions do?
|
Keep epithelial cells very close together (btw 2 adjacent cells)
Made up of 8 ptns The 8 ptns forms complexes Only very small molecules can get through ->bacteria cannot pass through |
|
|
What is the mucous gel layer?
(physical barrier 2) |
Separates bacteria from the epithelium
Helps stop the bacteria from getting to the tissue |
|
|
What are mucins?
|
Glycoptns
Secreted or mb-ass't Synthesized by goblet cells Contain regions rich in O-linked glycans (Ser/Thr) (Add 2 residues of Ser/Thr through N-linkage (by nitrogen)) (Glycans can form up to 80% of the mucin MW) |
|
|
Look at figure pg 3
|
look at figure pg 3
|
|
|
Can bacteria make it all the way through the mucous gel layer?
|
Probably not
-> There are antimicrobial peptides and IgA near the tissue cells |
|
|
What are the 2 layers colon mucous is organized in?
|
Inner layer
Outer layer |
|
|
Describe the inner layer.
|
Densely packed
Firmly attached to the epithelium and devoid of bacteria (or very few bacteria) |
|
|
Describe the outer layer.
|
Movable
Has an expanded volume Heavily colonized by bacteria Less dense mucous layer |
|
|
What does Muc2 do?
|
Build mucous barrier
|
|
|
How many genes are there in humans that code for mucins?
|
16 genes
(most these mucins are mb bound, but some, like Muc2, are secreted) |
|
|
What kind of mucin is Muc2?
|
Major colonic SECRETED mucin in humans/mice
|
|
|
What is the major structural component of BOTH our inner and outer mucosal layers?
|
Muc2
|
|
|
What happens to mice that are Muc2 -/- ?
What does this show? |
Develop spontaneous inflammation because the epithelium is in direct contact with bacteria
Shows PAMPs expressed by microbiota can cause infalmmation -Mucous layer cery important to maintain state of tolerance |
|
|
How is the firm, adherent layer of mucous (inner layer) converted to loose mucous (outer layer)?
|
By limited proteolysis (by bacteria ptns)
|
|
|
What ae AMPs?
|
Anti-microbial peptides
Chemical barrier of intestine |
|
|
What AMPs do Paneth cells secrete?
|
AMPs and AM-peptides such as:
α-defensins (AMPs) -> secreted in response to baterial signals α-defensins are HD5 and HD6 Known as cryptdins in mice (# of AMPs vary from species, as does the # of genes required to makes the AMPs) |
|
|
What do α-defensins do?
|
Somehow control the penetration of bacteria from the lumen to tissues
-Less efficient in the lumen and more efficient in the tissues, since higher concentration in tissues, compared to lower concentration of AMPs in the lumen (concentration gradient) |
|
|
Where are Paneth cells?
|
Bottom of microvilli
|
|
|
What happens when a transgenic mouse is made to express human HD5 in additionto its own cryptdins?
|
Results in changes in normal microflora and increased protection against challenge with Salmonella typhimurium
=> Proof that α-defensins are important in the small intestine (NOT secreted in the colon) |
|
|
What are the types of human α-defensins?
|
HNP-1
HNP-2 HNP-3 HNP-4 HD-5 HD-6 (HNPs: human neutropohils) (HDs: secreted by Paneth cells in the SI) |
|
|
Human neutrophils have largest amounts of which HNPs?
|
HNP-1,2,3
|
|
|
What are the conserved structures of α-defensins?
|
3 intramolecular disulfide bonds
β-sheet structures (like the β-defensin) |
|
|
What kind of granules are there (2)?
|
Specific granules:
Lactoferrin, hCAP18, lysozyme Azurophil Granules: α-defensin, lysozyme |
|
|
Describe β-defensins.
|
Human genome has many genes coding for this
Epithelial cells express β-defensins (mostly in colon, also in SI) Some are constitutively expressed (β-defensin 1) and others are induced by the recognition of PAMPs (β-defensin 2) |
|
|
Why do defensins interact preferentially with bacterial mbs?
|
Defensins have a positive charge
Bact mb has a negative charge ->peptide will lyse cells by forming pores in them |
|
|
What other activities can defensins have? (other than antibacterial activity)
|
Antiviral
Antifungal Immunomodulatory properties |
|
|
What are α-Helical AMPs?
|
Cathelicidins (in humans)
-> LL-37 (LL= 2 fisrt aa are Leu; 37= 37 aa in this ptn) -> CRAMP: cathelicidin related AMP, in mouse |
|
|
What are cathelicidins?
|
Amphipathic helices with a positively charged face
Have hydrophillic (+ charge) and hydrophobic (- charge) surfaes ->Net charge: +6 |
|
|
Why is it important that the cathelicidin has a net positive charge of +6?
|
Important to bind to bacterial surface
->Then peptide inserts into the mb through a pore -> hydrophobic residues interact with lipids ->Bacteria will lyse |
|
|
Why o defensins interact preferentially with bacterial mbs?
|
Defensins have a positive charge
Bact mb has a negative charge ->peptide will lyse cells by forming pores in them |
|
|
What other acitivities can defensins have? (other than antibacterial activity)
|
Antiviral
Antifungal Immunomodulatory properties |
|
|
What are α-Helical AMPs?
|
Cathelicidins (in humans)
-> LL-37 (LL= 2 fisrt aa are Leu; 37= 37 aa in this ptn) -> CRAMP: cathelicidin related AMP, in mouse |
|
|
What are cathelicidins?
|
Amphipathic helices with a positively charged face
Have hydrophillic (+ charge) and hydrophobic (- charge) surfaes ->Net charge: +6 |
|
|
Why is it important that the cathelicidin has a net positive charge of +6?
|
Important to bind to bacterial surface
->Then peptide inserts into the mb through a pore -> hydrophobic residues interact with lipids ->Bacteria will lyse |
|
|
How are all these AMPs formed?
|
Start as precursors (preproptns)
-Processed by proteases ->Trypsin in humans process α-defensins -> MMP-7 in mice process α-defensin |
|
|
What do these chemical barriers do?
|
Protect host from bacterial penetration
|
|
|
What are the Secretory immunoglobulins (SIgs)?
|
IgA (dimeric)
IgM (pentameric) |
|
|
What holds the dimers and pentamers together?
|
J (joining) chain
15 kDa polypeptide |
|
|
What synthesizes IgA?
|
Plasma cells of the lamina propria
|
|
|
What happens to the IgA Ab that are synthesized?
|
Transported through the mucosal epithelium
Secreted into the lumen |
|
|
How many grams of IgA are secreted/day?
|
3-5 g
|
|
|
What is the process of transcytosis of IgA?
|
Specific receptor expressed at cell surface of epithelial cells
Receptor binds IgA that are secreted by plasma cells -Induce endocytosis of IgA into vacuoles in the epithelial cells -Vacuoles migrate to Apilcal surface (towards the lumen, where the bacteria are) -IgA released into the lumen of epitehlium -IgA released through cleavage of the receptor by a protease -Part of the bacteria receptor will still be attached to the IgA or will float around -The ptn part (IgA) can bind to mucin and then recognize epitopes on bacteria and keep the bacteria in the mucin layer LOOK at figure pg 7 |
|
|
What is the IgA secreted by plasma cells made for? (2)
|
IgA directed vs specific bact
IgA made to sample the environment |
|
|
Describe Ag sampling
|
Ag presenting DCs in lamina propria extend their processes btw epithelial cells and into the gut of the lumen
.: they take up bacteria/Ag (but only get a sample of the bacteria that are near the epithelial surface and not in the middle of the lumen) |
|
|
What role do M (microfold) cells play in Ag sampling?
|
M cells are epithelial-like cells specialized in Ag-Capturing fcts
They're very permeable to Ag and IgA-bound Ag -will be recognized by DCs underneath, in the lamina propria -Will present Ag to T cells and B cells will thus be activated to make more IgA |
|
|
What is the role of IgA in Intestinal homeostasis?
|
1-Protect mucosal surface vs colonization and invasion by pathogenic/commensal bacteria. (keeps commensal bact from crossing host tissue)
2- Mediate apical-basolateral transcytosis of Ag across M cells and epithelial cells, for presentation to DCs in lamina propria 3- IgA Ab neutralize microbial products with proinflammatory activity (LPS, p/g) and .: limit inflammatory response |
|
|
What happens to mice that are kept under germ free conditions that lack the intestinal microflora?
|
Have highly reduced intestinal Iga
-> suggests direct correlation between IgA and commensals ->These mice won't produce IgA and will have very small Peyer's Patches -> Microflora are important for the development of the immune system |
|
|
What is a Probiotic?
|
Live microorganisms that are ingested to improve the balance of the GI tract microbiota
|
|
|
What are probiotics used for?
|
Supportive treatments for Inflammatory bowel diseases (IBDs) and C. difficil infections
|
|
|
What are some examples of probiotics?
|
-Lactobacillus rhamnosus GG, L. plantarum 299v and L.acidophilus (G+)
-Bifidobacterium longum and B. bifidum (G+) -E. colli Nissle 1917 (G-) -Saccharomyces boulardii (yeast) |
|
|
What are prebiotics?
|
Dietary supplements that stimulate the growth or activity of certain beneficial gut microbes
|
|
|
What is the problem with commensal E.coli strains isolated from humans?
|
Up to 34% of them produce the genotoxin colibactin
|
|
|
What does the genotoxin colibactin do?
|
Induces break in the DNA of eukarytoic cells in vitro and in vivo
->Possible link between the intestinal flora and colon cancer |
|
|
What is an example of such an E.coli strain?
|
E.coli strain Nissle 1917
(used as a probiotic for IBDs) produces fctnal genotoxin |
|
|
Describe how obesity is linked to gut flora.
|
Some genetic and hormonal factors (leptin) linked to obesity
Mice that are genetically obese (ob/ob) gene mutation that prevent production of active leptin Have 50% less Bacteroides and correspondingly more Firmicutes than WT mice (bacteroides digest the polysac that the body cannot) The relative proportion of Bacteroidetes is decreased in obese ppl by comparison with lean ppl (n=12) When obese ppl lose weight over a year, the proportion of Bacteroidetes increases |
|
|
How does the gut microbiota contribute to obesity?
|
By extracting more or less E from the diet
|
|
|
What happens ot mice that don't have TLR-5? (which is expressed by epithelial cells)
|
These mice were more obese
Had many characteristics of metabolic syndrom |
|
|
What happens when thes mice are treated with antibiotics to kill 80% of their microflora?
|
Reverse the metabolic syndrome
|
|
|
What happens when bacteria fromthese mice are transferred from the gut of obese mice to normal germ-free mice?
|
They were able to produce the metabolic syndrom of the obese mice (insulin resistance, etc)
|
|
|
What does this experiment show?
|
Gut microbiota of these obese mice was necessary and sufficient for the resulting obesity
->found there was a relatioinship btw recognition of bacteria, inflammation and metabolic syndrom of obesity |
|
|
What happens to ppl with IBDs?
|
Inflammation to intestinal bacteria is not downregulated to a state of tolerance (always some lvl of inflammation)
|
|
|
What are the geneteic predispositions to IBDs?
|
Mutations in the intracellular pattern-recognition receptor NOD2 leads to a defect in the secretion of α-defensins by Paneth cells predisposes to IBDs
(NOD2 is a receptor that rec'z p/g) |
|
|
Why don't germ-free mice not develop chemically induced IBDs?
|
Suggests that microbiota play a critical role in IBD
|
|
|
Do we know if microbiota is the cause or consequence of IBDs (Ulcerative colitis and Crohn's disease)?
|
Might be more the result of the genetic imbalance than the cause of these diseases
->no α-defensins .: more bacteria colonized and changed the microbiota composition i.e: Mycobacterim avium and adherent-invasive E. coli (AIEC) |
|
|
What is the proposed model for the fct of intestinal bacteria and host defensins in the pathogenesis of Crohn's disease?
|
NORMAL
Have a balance btw inflammatory response and microbiota (because microbiota doesn't really get to epithelial surface, so no inflammation) GENETIC IMBALANCE -Produce less defensin/ defect in a physical or chemical barrier -Bacteria reach the epithelium -Produce more inflammation -Develop disease |
