Lecture 10 : microflora and mucosal immune system

Question 1

What are the** multiple physical barriers** in the GIT?

Answer 1

• saliva in the oral cavity - eg lyzozyme kills bacteria
• there are tight junctions in the epithelium of the GIT and these restrict diffusion of solutes etc
• HCL in the stomach

Question 2

What is MALT?

Answer 2

• mucosa associated lymphoid tissue - the lymphoid tissue distributed in the mucosa
• eg appendix and peyers patches in the ileum

Question 3

What is GALT?

Answer 3

• Gut associated lymphoid tissue
• lymphoid aggregates throughout the GIT

Question 4

Describe are the **functions of microbes **in the GIT?

Answer 4

* protective functions - can produce antimicrobial factors & they compete with bacteria for nutrients / receptors
* **structural functions **- apical tightening of junctions - forms a barrier between cells & can tighten in response to harmful bacteria
* metabolic functions - synthesize vitamins & ion absorption
*

Question 5

how are microbes in the GIT distributed?

Answer 5

• Microbes are distributed across the GIT
• less in stomach due to HCL
• large density of bacteria in colon

Question 6

what factors affect our microbial composition?

Answer 6

• the delivery procedure during birth - ie vaginal or c section
• whether baby is breast fed or bottle fed
• age
• antibiotics (deplete microbiota)
• lifestyle - ie active / exercise

Question 7

what are examples of cell types in the mucosal immune system of the GIT?

Answer 7

• Lymphocytes
• macrophages
• dendritic cells
• neutrophils
• epithelial cells
• goblet cells
• paneth cells ( in crypt)

Question 8

Describe lymphocytes

what are they, types, where do these types mature, where do they move to

Answer 8

• type of white blood cell found in the immune system
• they **include natural killer T cells and B cells **
• B cells mature in bone marrow & T cells mature in the thymus (organ in chest)
• they are concentrated in lymphoid organs and tissues / lymphoid aggregates eg peyers patches

Question 9

What are the molecular differences between T and B lymphocytes?

Answer 9

• the helper T cells have a toll like receptor & CD4 protein
• the cytotoxic T cells have a toll like receptor & CD8 protein
• B lymphocytes contain B cell receptors

Question 10

How does an undifferentiated T helper cell differentiate?

Answer 10

• by exposure to certain molecules
• eg undifferentiated T helper on exposure to IL-4 forms B cells
  *

Question 11

What are macrophages?

Answer 11

type of white blood cell that engulf and digest pathogens via phagocytosis

Question 12

what are denditic cells?

Answer 12

• a type of phagocyte that sends its long processes out through the tight junctions to collect the antigen and then presents it to other immune cells

Question 13

What are neutrophils?

Answer 13

type of white blood cell that are the first responders to infection

Question 14

What are phagocytes?

Answer 14

they are cells that protect the body by ingesting foreign particles eg bacteria

Question 15

How do goblet cells contribute to the mucosal immune function?

Answer 15

they form a protective secretion that is composed of mucin and lysozyme

Question 16

what are paneth cells?

Answer 16

• immune cells in the mucosa
• when exposed to bacteria, paneth cells secrete antimicrobial peptides and proteins

Question 17

What are** M cells/ micro fold cells**?

Answer 17

• unique to GALT
• they have no microvilli, they sit on the epithelial surface, between enterocytes
• they are also in close contact with lymphocytes & dendritic cells

Question 18

How do M cells work?

Answer 18

• M cells take up antigens from the gut lumen by endocytosis
• antigens are released beneath M cells and taken up by antigen presenting dendritic cells

Question 19

what does NOD receptor stand for?

Answer 19

• Nucleotide binding and oligomerisation domain like receptor

Question 20

How do NOD like receptors work?

Answer 20

• they recognise pattern associated molecular patterns (PAMPS)
• they signal via caspase activation
• they can co operate with toll like receptors and regulate inflammatory and apoptotic response

Question 21

What Inflammatory bowel disease?

Answer 21

• term used to describe disorders that involves chronic inflammation of the GIT
• types of IBD include ulcerative colitis or Crohn’s disease

Question 22

What ulcerative colitis?

Answer 22

• inflammation and ulcers of the colon and rectum
• symptoms include diarrhea,weight loss, intestinal bleeding

Question 23

What is C.diffcile?

Answer 23

• a condition that involves over-colonisation of the microbiome with C.diff
• may occur after the use of broad spectrum antibiotics
• infection is usually **hospital acquired **
• C.dificile** produces toxins** that **damage the lining **of the colon