Celiac Disease Flashcards
1
Q
Celiac Disease
A
- chronic inflammatory disease primarily affecting small intestine
- results from inflammatory response initiated by dietary gluten (NOT allergic response)
- inflammation leads to damage and atrophy of intestinal villae - villae lose absorption capability, breach in the epithelial barrier can lead to increased risk of infection
2
Q
Many genes are associated with celiac disease, but the most important is…
A
the human leukocyte antigen (HLA) gene cluster
3
Q
What are some increased risks associated with celiac disease? Why?
A
micronutrient/macronutrient deficiencies
* loss of intestinal structure associated with nutrient malabsorption
intestinal cancer
* constant cycles of cell division and attempts to repair intestinal epithelial cell damage
4
Q
what is the role of the the human leukocyte antigen (HLA) gene cluster?
A
codes for the receptor chains (alpha and beta) of MHC class 2 receptors.
5
Q
What are the main components of the human leukocyte antigen (HLA) MCH class 2 receptor coding genes?
Which is most important?
A
- DP
- DQ - most important
- DR
6
Q
What is Gluten?
A
all proteins from wheat, barley and rye
7
Q
True or False, in celiac disease, patients protein digestion (enzyme function) and absorption is NORMAL
A
True: problem in celiac disease is that the immune response against gluten results in damage to the small intestine epithelial barrier, lamina propria and intestine tissue structure
8
Q
MHC Class 2 receptors are ____dimers.
A
heterodimers
9
Q
Which loci on the human leukocyte antigen (HLA) gene cluster is most important for the development of celiac disease? Which forms of this loci specifically?
A
The DQ is the most important!
- HLA-DQ2
- HLA-DQ8
- (also some evidence of HLA-DQ7)
10
Q
Tight Junctions
A
Seal neighbouring cells together - prevent leakage between epithelial cells
11
Q
What proteins anchor the tight junction to the zona occludins
A
- Claudins
- JAMs
- Occludins
12
Q
MCH Class 2
A
heterodimer on the surface of the APC that presents to CD4 T+ cells
13
Q
True or Flase: there is a high degree of variation in the MCH Class 2 alpha and beta chains in the human population.
A
True
14
Q
How do HLA-DQ2/8 (and possibly 7) loci initiate a gluten immune response?
A
They allow MCH Class 2 cells to tightly bind gluten to initate T Cell response.
15
Q
What binds to the actin cytoskeleton to structurally hold the junctional complex of the tight junction together?
A
zona occludins
16
Q
Adherens junction
A
- Join actin bundle in one cell to the next
- cadherins and catenins
17
Q
True or False: Most people with the HLA-DQ2/8 loci test positive for celiac disease.
A
False.
20-30% have DQ2/DQ8, and only 1% of those actually have celiac disease.
18
Q
Lamina Propria
A
- below epithelial barrier
- where CD immune response is generated
19
Q
What are the three components of the apical junctional complexes?
A
- Tight junctions
- Adherens Junctions
- Gap Junctions
20
Q
What is the role of tissue transglutaminase (TTG)?
A
- TTG deamidates glutamine residues in gluten to produce a negative charge (post-translation)
- increases the likelyhood of gluent and DQ interaction.
- HLA-DQ2 has high affinity for negative residues in positions 4, 6, and 7 in it antigen-binding groove.
- HLA-DQ8 has high affinity for negative residues in positions 1 and 9 in it antigen-binding groove.
21
Q
RhoA
A
- functions as an adaptor protein
- central role in regulating cell shape and polarity through its effects on actin polymerization, cell adhesion and structure of actin cytoskeleton
22
Q
Where does tissue transglutaminase (TTG) come from (3)?
A
- produced in intestinal epithelial cells (secreted basolaterally into lamina propria and apically into the lumen)
- secreted my microbiota
- found in processed foods.
23
Q
Cdc42
A
- functions as an adaptor protein
- regulates cell polarity and cell morphology
- supports formation of actin filaments and integrity of actin cytoskeleton
24
Q
What two molecules play a key role in cell migration?
A
RhoA and Cdc42
* movement of epithelial cells to fill a gap or breach in the epithelial barrier - key in wound healing
25
transglutaminases function to...
promote protein cross-linking
26
Desmosome
* intercellular junction that provides strong adhesion between cells
* link to the intermediate filament cytoskeleton
27
What are the components of HLA-DQ2?
- (gluten) antigen-binding domains in positions 4, 6, and 7.
- positive charges in the positions in which the AA of the antigen fits into the MCH molecule.
28
What are the components of HLA-DQ8?
- (gluten) antigen-binding domains in positions 1and 9.
- positive charges in the positions in which the AA of the antigen fits into the MCH molecule.
29
What are the characteristics of a HEALTHY epithelial membrane barrier
* less permeable, high integrity
* mucus secretion -> protective mucus barrier
* high expression and function of apical junctional complex components -> hold epithelial cells tightly together
* no space for lumen contents like gluten to pass between epithelial cells
30
True or False: binding of gluten to the MCH molecule will occur in the basence of tissue transglutaminase (TTG).
False.
It makes the response bigger, but does cause the response completely. **amplification due to increased T-Cell activation!!**
31
What are the characteristics of an UNHEALTHY / LEAKY epithelial membrane barrier
* reduced mucus secretion -> loss of protective mucus layer
* decrease junctional complex protein expression (open circles where they are missing)
* lumen contents like gluten can pass between epithelial cells and access the blood stream or remain in the lamina propria and encounter immune cells
32
deamidated gluent peptides are presented by HLA-DQ2/8 to...
T-Cells.
33
What is the START of the immune response in celiac disease
Antigen presenting cell presents gluten (antigen) to a T cells in the lamina propria of the small intestine
34
35
describe the steps of antigen presentation to T-cells starting from tissue transglutaminase (TTG).
- tissue transglutaminase (TTG) deamidates the glutamine residue (makes negative) to increase affinity for HLA-DQ on MCH class 2 receptors.
- gluten binds to HLA-DQ2/8 of APC
- APC (HLA-DQ2/8) presents gluten to TCR of T-cell.
- T cell intiates immune response.
36
What are the two types of APCs?
* dendritic cell
* macrophage
37
What are the two types of lymphocytes?
* T cells
* B cells
38
Where are immune cells (APCs, B cells, T cells) located?
* Peyer's patches (localized follicules of immune cells)
* Lamina Propria
39
M cells
dispersed throughout epithelial barrier that covers a Peyer's patch
40
What does an APC do with an antigen?
1. **Uptake:** phagocytose the antigen
2. **Process:** cleave the larger antigen protein into a smaller sequence of amino acids
3. **Present:** smaller antigen fragment is presented on the surface of the APC by an MHC class I or class II molecule. Celiac disease uses MHCII to present the antigen to the CD4 T cell
41
When presented gluten by an APC, the t cell induces an immune response that includes the following (3):
- T cell activation, differentiation (Th1) and proliferation.
- cytokine release of IFNγ
- matrix metalloprotease activity (MMP).
| ALL OF THE ABOVE LEAD TO TISSUE DAMAGE
42
What is T0 cell?
The T-Cell that is presented to by the APC (i.e. the one that first encounters gluten).
43
Where is an MHC class II molecule located and where and to what does it bind?
MHC class II on the surface of the APC binds with the T cell receptor on the surface of CD4 T cell
44
What is a TH1 cell?
after presentation, the t-cell (T0) differentiates into a T-helper cell (TH1).
45
What does TH1 do upon its creation?
increases expression of **Tbet** to produce many TH1 clones **(clonal expansion)**.
46
What do the TH1 clone army secrete?
- interferon-γ (AKA INF-γ)
- IL-21
47
In order for an APC to phagocytose gluten and process and present the gluten to a T cell, the gluten has to get from ____ to ____
lumen of the small intestine ; lamina propria (where APCs are located)
48
What does INF-γ do?
- triggers MMP-12 and MMP-13 activation.
- activates APCs in the lamina propria to trigger TNFα (which activates MMP-1 and MMP-3).
- stimulates TTG activation thru activation of Thioredoxin-1.
| MMPs lead to epithelial apoptosis and extracellular matrix degradation.
49
What are the three major methods of APC capture of luminal antigens to start the immune response in celiac disease?
1. M cell mediated transcytosis: gluten passes freely through the M cell and an APC in the lamina propria picks it up
2. Luminal capture by periscoping across endothelial cell
3. Luminal capture through M cell transcellular pores
50
What does IL-21 do?
- furthers TH1 response by activating IELs (AKA CD8+ T cells and NK cells) to promote epithelial cell apoptosis and loss of barrier integrity.
- amplifies effects of IL-15 (promotes epithelial cell apoptosis via MIC-A epression).
- activates B Cells for antibody production.
51
What produces IL-15?
APCs
52
What is MIC-A? What stimulates its expression? What does it induce?
- secretion induced due to IL-15 (APC cells).
- MIC-A is the ligand for NKG2D (found on IEL) cell epithelial barrier.
- bind of MIC-A to NKG2D leads to IEL activation and proliferation.
53
IEL activation and proliferation is a cell ____ reaction. (dependent or independent).
**dependent** (MIC-A binding to NKG2D)
54
IELs lead to epithelial cell apoptosis through 2 mechanisms. What are they?
1. **CELL CONTACT DEPENDENT**: FasLigand (on IEL surafce) to FAS (on epithelial cell surafce).
2. **CELL-CONTACT INDEPENDENT*: perforin and granzyme secretion.
| BOTH THESE RESPONSE HAPPEN AT THE SAME TIME!
55
How do perforins function?
they poke holes in the epithelial cell plasma membrane.
56
How do granzymes work?
they enter the epithelial cell and activate caspase-3 to trigger cell apoptosis.
57
as damage to in intestinal muscosa occurs, one can see...
progressive loss of small intestinal villi and microvilli structure
| loss of structure = loss of function
58
Where are B Cells found?
lamina propria and payers patches.
59
B cells release antibodies against... (6)
- gluent (gliadin and glutenin)
- tissue transglutaminase (TTG)
- collagen (extracellular matrix component of the lamina propria).
- actin (in muscle layer of small intestine)
- endomysium (in connective tissue layer of small intestine).
60
In celiac disease, B cells produce ____ - antibodies against ____.
self-antibodies, structural components of the small intestine.
61
where are anti-gluten antibodies found?
lumen of the intestine AND lamina propria.
62
What type of Th response is in celiac disease? What do these T cells release?
Th1 -> release of IFNy
63
True or False: anti-gluten antibodies act to protect the body from gluten.
**FALSE!**
they form a complex with CD71, which is a recptor on the apical surface of epithelial cells.
64
TH0
naive T cell -> never encountered an antigen before
65
clonal expansion of T cells
once naive T cells are activated, they will differentiate into a T helper cell subset and proliferate to form many T cell clones
66
What is the role of CD71?
- forms a complex with anti-gluten antibodies.
- transports gluten into lamina propria (retrotransport).
- brings gluten in contact with TTGs.
67
What directs the development of each T cell subset?
activation of specific transcription factors
68
Tbet
transcription factor that directs naive T cells to develop into TH1 cells
69
Tregs
* important for stopping the celiac disease immune response
* suppress over-reactive inflammatory T cell responses such as TH1 in celiac disease
* secrete IL-10
* suppressed in celiac disease
70
Describe how CD71 works and which its bad.
- anti-gluten antibodies bind gluten moecules.
- CD17 binds anti-gluten antibodies (which are attached to gluten moecules)
- transports the antibody (and gluten) into the lamina propria.
- perpetuates immune response.
71
FOXP3
transcription factor that directs the differentiation of naive T cells into Treg cells
72
What are the 2 classes of protein in wheat?
Gliadins and Glutenins
73
What protein does barley contain?
Hordeins
74
What protein does rye contain?
Secalins
75
Why are anti-transglutaminase antibodies bad?
- TTG enzyme in the lamina normally binds to fibronectin in the extracellular matix (ECM) to help with ECM assembly.
- when the anti-TTG destroys the enzymes, it prevents the body from repairing the ECM and restoring the epithelial barrier.
76
What are prolamins and what are their characteristics?
* proteins in gluten that trigger an immune response in patients with celiac disease
* high glutamine content
* high proline content
77
Do oats stimulate a celiac disease immune response? Why or why not?
No. They contain aveinin proteins which are high in glutamine but NOT proline
78
Whats the role of Zonulin in celiac disease?
- gluten increases increase zonulin expression.
- zonulin binds to CXCR3 receptor on epithelial cell apical membrane (overexpressed in those w CD)
- Zonulin-CXCR3 signalling loosens the tight junctions between epithelial cells.
- leads to increase permeability of the epithelial barrier.
- this lets more gluten enters, and worsens response.
79
How does proline contribute to celiac disease?
high proline content makes proteins resistant to digestion by gastric, pancreatic and brush border enzymes
80
How does glutamine contribute to celiac disease?
high glutamine content makes gluten proteins excellent substrates for deamidation reactions by **tissue transglutaminase**
81
What does tissue transglutaminase do?
converts glutamine (neutral charge) to glutamate (negative charge)
82
What genes/proteins are overexpressed in celiac disease (6)?
- zonulin
- CXCR3
- CD71
- MIC-A
- TTG
- IRF4
83
What is IRF4?
transcription factor that regulated IL-21 expression.
84
What does IL-15 do?
inhibits Regulatory T Cells (Tregs) which results in an ongoing TH1 response.
85
What results from the presence of high glutamine and proline molecules in the small intestine?
* not absorbed by intestinal epithelial cell
* large peptides with high glutamine and proline content remain in the intestine where they stimulate an immiune response and cause tissue damage
86
Main symptoms of celiac disease are ____, including...
**extra-intestinal**
- anemia
- osteoporosis
- *dermititis herpetiformis*
87
T/F: CD patients have abnormally functioning protein digestion and absorption capabilities in non-damaged regions of the small intestine
false: CD patients do not digest gluten any differently from people without celiac disease
88
What is the connection between Type 1 Diabetes (T1D) and celiac disease?
- TD1 leads to increased intestinal permeability
- TD1 leads to elevated zonulin levels
- both disorders share common HLA-DQ2 haplotype.
89
90
Which serology test are used to test?
- (IgG) anti-gliadin
- (IgA) anti-gliadin and anti-glutenin
- (IgA) anti-TTG
