3.1 Mucosal protection in the gut

Question 1

What are the two anti-microbial substances produced by the normal gut flora?

Answer 1

Short chain fatty acids and bacreriocins

Question 2

Name three chemical defences and how are the protective?

Answer 2

Bile, pepsin and gastric acid

All antimicrobial

Question 3

What is the major component of mucus

Answer 3

glycoproteins

Question 4

What are the mucus secreting cells in the stomach?

Answer 4

Surface and neck mucus cells

Question 5

What are the mucus secreting cells in the small and large intestine?

Answer 5

Brunners glands and goblet cells

Question 6

what are two ways mucus cells protect epithelial cells from microbial insult?

Answer 6

They form a barrier for clonization and they contain IgA which will expel the organism

Question 7

What are the three types of protective mechanisms in the gut?

Answer 7

Microbiological
Chemical
Physical

Question 8

How does the normal gut flora protect the host against pathogens?

Answer 8

It will compete with the pathogenic organisms for nutrients and attachment sites on epithelial cells
It will also produce antimicrobial substances that can kill or inhibit growth of invading pathogens and prevent their colonization (short chain fatty acids and bacteriocins)

Question 9

What is the physical mucosal protection of the gut?

Answer 9

A single layer of intestinal epithelial cells providing a physical barrier between the lamina propria and intestinal lumen that contains the normal gut flora and pathogens

Question 10

What functions do tight junctions play?

Answer 10

They hold together the epithelial cells forming a seal against the external environment - infection can only occur

Question 11

What is the role of epithelial cell turnover and peristalsis?

Answer 11

Intestinal epithelial cell turnover is constant shedding of cells damaged by microbial infection or stresses and replenishment by neighbouring epithelial cells - this will help expel pathogens and prevent overgrowth of normal gut flora

Question 12

What is the role of gastic mucus?

Answer 12

It is acid resistant preventing the HCl from breaking down he epithelium - secreted bicarbonate ions establishing a pH gradient

Question 13

how does H.pylori cause infection?

Answer 13

It can swim through teh gastric mucus in teh stomach and attach to epithelial cells beneath where it can cause inflammation

Question 14

How does pathogneic E.Coli cause infection?

Answer 14

Produces proteins that specifically degrade mucin to gain access to intestinal epithelium

Question 15

What cell types are present in Peyers patches and what is its structure?

Answer 15

B cell follicles with germinal centres and smaller T cell area
There is a sunepithelial dome which is rich in dendritic cells B and T cells

Layer of follicle associated epithelium containing conventional intestinal epithelial cells (enterocytes) and fewer specialised cells (microfold M cells)

Question 16

What are isolated lymphoid follicles composed of

Answer 16

composed of epithelium containing M cells but with mainly B cells (develop after birth)

Question 17

How do peyers patched uptake antigens?

Answer 17

M cells take up antigen by endocytosis and phagocytosis

Antigen is transported across the M cells in vesicles and released at the basal surface

Antigen is bound by dendritic cells which activates T cells

Question 18

How do dendritic cells directly uptake antigens?

Answer 18

They extend their processes across the epithelial layer to capture the antigen from the lumen of the gut

Question 19

What are the two forms of antigen uptake?

Answer 19

Uptake by peyers patched mediated by M cells

Direct uptake by dendritic cells

Question 20

Where are CD8 and CD4 T cells mainly located?

Answer 20

CD4 in the lamina propria

CD8 in the epithelium

Question 21

What are the immunologic properties of the lamina propria?

Answer 21

CD4 T cells, IgA producing plasma cells, macrophages, dendritic cells and mast cells

Question 22

What are the immunological properties of the epithelium?

Answer 22

CD8 T cells

Question 23

What is the role of epithelial cells in immune response and what is their structure?

Answer 23

contain receptors on their basal surface allowing them to recognise bacteria that have invaded the epithelial barrier
The basolateral surface contain toll like receptors
The cytoplasm contain nuceltotide binding oligomerisation proteins (NODs)

Question 24

What occurs when epithelial cells recognise pathogens?

Answer 24

There is an influx of inflammatory cells/lymphocytes into the mucosa from the blood stream

• Endocytosed bacteria are recognise by TLRs
• Bacteria or their products in the cytosol recognised by NOD1 and NOD2

Question 25

How does IgA cause an immune response?

Answer 25

It is translocated to the apical surface of teh epithelium where it can bind and neutralize pathogens and toxins, neutralize antigens internalized in endosomes and export toxins and pathogens from the lamina propria while being secreted

Question 26

What is the CD4 immune response?

Answer 26

Pathogens that penetrate the epithelium will activate dendritic cells to give a strong co-stimulatory signal to cause naive T cells to develop into CD4 Th1 and Th2 cells which are macrophage activating cytokines and cytokines that stimulate B cells to produce antibodies respectively

Question 27

What is the CD8 immune response?

Answer 27

peptides from invasive organisms bound to MHC class 1 on infected epithelial cells will be recognised by intraepthelial lympocytes (CD8 T cells) which will then release anti-microbial substances killing the infected cell

Question 28

What prevents an immune response to normal flora?

Answer 28

In the presence of commensal bacteria the production of PGE2, TGF-b and TLSP inhibits dendritic cell maturation. The immature dendritic cells give weak signals for naive CD4 T cells to differentiate into T reg cells (Th3) which produces IL-10 (anti-inflammatory cytokine)

Question 29

which effector cell will you encounter in the gut epithelium?

Answer 29

CD8

Question 30

what is the function of IgA

Answer 30

Neutralize pathogens and toxins