Mucosal immunity and diseases (Paul de Vos)

12 important questions on Mucosal immunity and diseases (Paul de Vos)

How does IgA cause the neutralizing and immunization of toxins?

1) Secreted IgA (through endocytosis) on the gut surface can bind and neutralize pathogens and toxins.

2) IgA is able to bind and neutralize antigens internalized in endosomes.

3) IgA can export toxins and pathogens from the lamina propria while being secreted.

When it goes wrong and bacteria come in: describe the neutrophil extracellular trap (NETosis)

Upon activation of the neutrophil receptors, neutrophil release granule proteins and chromatin that together form extracellular fibers that bind Gram-positive and -negative bacteria. The fibers trap the microorganims.

NET formation is associated with bacterial clearance, but also with thrombosis, sepsis and SLE.

We cannot live without commensals. What are the 4 uses of commensals?

1) Stimulates mucosal and epithelial barrier function.
- produce small chain fatty acids (SCFA)
- stimulates mucus production.

2) Inhibit pathogenic bacteria
- by decreasing luminal pH,  bacteriocidal proteins, blocking epithelial binding

3) Immunoregulatory
- Stimulates anti-inflammatory cytokines (IL10 and TGF-b)
- Stimulates IgA production

4) Mandatory for our metabolism
- primary source vitamins
- digestion of complex diet components (cellulose)
- source for SCFA
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Behind the epithelium lies GALT (Gut associated lymphoid tissue). What kind of receptor keep the balance between immunity versus tolerance?

Pattern recognition receptors (PRRs) expressed by immune cells & epithelial cells.

What is the physiological role of zonulin?

Zonulin increases permeability which changes the hydrostatic water pressure which bring water in intestinal lumen. Through this water the removal of pathogens from the human body can occur (diarrhea).

What is the pathophysiological role of zonulin in celiac disease?

1) Gliadin (immunemodulating component of gluten) stimulates the CXCR3 chemokine receptor.

2) Release of zonulin.

3) Zonulin causes claudin modification in the tight junction and causes a increase of permeability, gliadin now passes the lamina propria.

4) After deamination gliadin binds to MHC or HLA on APC or on CXCR3 expressing cells such as APCs, NK cells and T cells.

5) Cytokines are released by APCs and gliadin is presented to T cells.

6) The final outcome entails a huge activation of both humoral and cellular nature.

How can leaky gut be related to type 1 diabetes?

Intraluminal zonulin concentration is 35 fold higher in diabetec prone mice. There is a 70% reduction in diabetes incidence by blockade of zonulin receptor. Absense of formation of islet cell antigens.

Which molecule causes the blockage in tight junctions for molecules > 3.5 kDa?

Claudin and occludin

Which receptors and cytokines differ in APC to differentiate a CD4/CD8 or Treg cell?

Treg -> NLRs
Th# -> TLRs

What is the normal processing of macromolecules (< 3.5 kDa) through epithelial cells from intenstinal lumen?

The macromolecules are broken down to nonimmunogenic molecules (tolerance induction)

Naive T cells that enter Peyer's patches from blood vessels directed by the homing receptor CCR7 and L-selectin. Describe how the homing progresses further, and how different chemokine receptors determine homing in the small and large intestines.

1) T cells in the Peyer's patch encounter antigen transported accros M cells and become activated by dendritic cells.

2) Activated T cells drain via mesenteric lymph nodes to the thoracic duct and return to the gut via the bloodstream.

3) Gut-homing effector T cells bind MAdCAM-1 on endothelium.

4) Activated T cells expressing alpha-4B7 integrin and CCR9 home into the small intestine.
T cells expressing CCR10 home into the  large intestine.     

In the lamina propria it is decided whether the mature T cells differentiate into intra-epithelial lymphocytes. How is this organized and what does this allow?

The lymphocytes loose alpha4-B7 and express alphaE-B7.

This allows binding to E-cadherin on epithelium.

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