IMMUNOLOGY OF THE GUT

Question 1

Outline the organisation of the intestinal flora as you move further down the gut?

Answer 1

the concentration of bacteria incresses and the more anaerobic the bacterua become

Question 2

whats the function of the intestinal flora?

Answer 2

produce vitamins
digest food components that we cant
mounts protective immune responses

Question 3

whats the most predominant cell in the small intestine?

Answer 3

enterocytes

Question 4

whats the most predominant cell in the large intestine?

Answer 4

colonocytes

Question 5

outline the differences in intestinal epithelium in small vs large intestine?

Answer 5

small has enterocytes and large colonocytes
small has paneth cells and large does not
small has villi whereas large does not
large insteastine also doesnt have plicae circularis like the small intestine

Question 6

what is goblet cells’ function in the epithelium of the small and large intestine?

Answer 6

secrete mucins (high molecular weight glycoproteins) to form the mucus layer

Question 7

whats the function of Paneth cells?

Answer 7

to secrete antimicrobial peptides

Question 8

what are the lymph nodes found all around the GIT?

Answer 8

mesenteric lymph nodes

Question 9

what are the 3 subsets of CD4+ Th cells?

Answer 9

effector subsets and regulatory subsets and follicular helper cells

Question 10

what are the effector CD4+ Th cells?

Answer 10

Th1
Th2
Th17

Question 11

what are the regulatory CD4+ Th cells?

Answer 11

Tr1 Th3 CD25+

Question 12

what cytokines do Th1 release?

Answer 12

IFN gamma

Question 13

what cytokines do Th2 release?

Answer 13

IL=4 IL-5

Question 14

what cytokines do Th17 release?

Answer 14

IL-17

Question 15

what cytokines do Tr1 release?

Answer 15

IL-10

Question 16

what cytokines do Th3 release?

Answer 16

TGF beta

Question 17

what do effector CD4+ Th cells do?

Answer 17

help us fight pathogens

Question 18

what do regulatory CD4+ Th cells do?

Answer 18

regulate/damoen the effectors

Question 19

what makes up the organized tissues in GALT?

Answer 19

peyers patches
isolated lymphoid follicles
mesenteric lymph nodes

Question 20

what makes up GALT?

Answer 20

the multi-follicular Peyer’s patches of the ileum
the vermiform appendix
the numerous isolated lymphoid follicles which are distributed along the length of the intestine

Question 21

what are the specialized epithelial cells of peyers patches?

Answer 21

Microfold (M) cells

Question 22

what are M cells function?

Answer 22

actively transport luminal antigens to the underlying lymphoid follicles to initiate an immune response - they pass the antigens to dendritic cells (transcyotosis)

Question 23

whats the most abundant antibody in mucosal secretions?

Answer 23

iga

Question 24

what is lamina propria?

Answer 24

connective tissue areas containing activated immune cells

Question 25

whats the difference between IgA in the blood and in mucosal tissue?

Answer 25

in the blood IgA is monomeric and in the mucosal tissue its dimeric

Question 26

whats the structure of dimeric IgA?

Answer 26

2 IgA connected by a J chain

Question 27

how does secretory IgA form?

Answer 27

The dimeric IgA-J chain complex is produced by B lymphocytes in the submucosal tissues. The secretory component is produced by mucosal epithelial cells and acts as a receptor for dimeric IgA.

Question 28

whats the function of secretory IgA?

Answer 28

limits the acess of pathogens to the mucosal surfaces without risking inflammatory damage

Question 29

Why doesnt the commensal flora trigger inflammation?

Answer 29

TLR4 is expressed at the base of the crypts where you wouldnt see many commensals. TLR5 is expressed on the basolateral side. So pathogens invading tissues can trigger TLR activation unlike commensals.
Pathogens often have virulence factors unlike commensals.
Commensals can actually change their flagellin sequence so it doesnt bind as strongly to TLR5 making them TLR5 hyporesponsive.