GI immunology

Question 1

List the pattern recognition receptors (PRRs).

Answer 1

Toll-like receptors, NOD-like receptoes, RigI-like receptors, C-type lectins, scavenger receptors

Question 2

What are PRRs?

Answer 2

Antigen recognition receptors in the innate immune system. Each immune cell carries an identical receptor of a given type.

Question 3

What are the two main groups of PRRs?

Answer 3

1. Cell surface (transmembrane) and intracellular receptors – TLRs, NLRs, RLR’s and CLR’s
2. Fluid-phase soluble molecules

Question 4

What do PRRs respond to?

Answer 4

PAMPs (pathogen-associated molecular patterns) and DAMPs (danger-associated molecular patterns).

Question 5

What are the central features of the adaptive immune system?

Answer 5

Unique antigen receptor found on each lymphocyte

In response to infection this lymphocyte undergoes clonal expansion

Question 6

What are the innate components of the GI immune system?

Answer 6

Commensals, epithelial barrier, molecular factors produced by epithelial cells.

Question 7

What are the adaptive components of the GI immune system?

Answer 7

Gut-associated lymphoid tissue (GALT)

Question 8

What are M cells?

Answer 8

microfold cells - found in the follicle-associated epithelium of the Peyer’s patch; have the unique ability to sample Ag from the lumen of the small intestine and deliver it via transcytosis to APC and lymphocytes located in a unique pocket-like structure on their basolateral side. Lack microvilli - have microfolds.

Question 9

Name some of the beneficial members of the gut flora?

Answer 9

Lactobacilli and bifidobacterium.

Question 10

At how many years is the colonic microflora considered to be adult-like?

Answer 10

2 years.

Question 11

What are prebiotics and what is a good source of these in infancy?

Answer 11

Non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and thus improves host health. Breast milk is a good source (inulin-type fructans).

Question 12

What are probiotics?

Answer 12

Live microorganisms which when administered in adequate amounts confer a health benefit on the host.

Question 13

What are the benefits of GI microflora?

Answer 13

Resistance to colonisation by pathogens, stimulate local immunity, oral tolerance, nutrition, epithelial cell turnover, intestinal motility.

Question 14

What are the hazards of GI microflora?

Answer 14

Around 15% pathogenic bacteria. Extraintestinal disease; septicaemia, autoimmunity; reactive arthritis
Allergy

Question 15

What is eubiosis?

Answer 15

A state on balance in the GI microflora.

Question 16

What is dysbiosis?

Answer 16

A state of imbalance in the GI microflora.

Question 17

How does the epithelial barrier contribute to GI immunology?

Answer 17

Prevents penetration by microorganisms. Intestinal mucosal barrier is a single cell layer. Self-renewing system undergoing continuous renewal from stem cells located near the base of the crypts of Lieberkhun.

Question 18

How do goblet cells contribute to GI immunology?

Answer 18

Produce mucins to provide for mucus layers that resist microbial access

Question 19

How do enterocytes contribute to GI immunology?

Answer 19

Produce antimicrobial peptides (defensins, lysozyme, lactoferrin, cathelicidins).
Mechanical action.

Question 20

Which class of Ig is secreted by the gastric mucosa?

Answer 20

IgA

Question 21

What are mucosal follicles?

Answer 21

Organised mucosal associated lymphoid tissue. Aggregate in Peyer’s patches or exist as single follicles.

Question 22

What proportion of intraepithelial lymphocytes are T cells?

Answer 22

90%

Question 23

What are the two main types of lymphocytes associated with the gut?

Answer 23

Intraepithelial lymphocytes (CD8) and Lamina Propria lymphocytes (CD4).

Question 24

In which layer of the gut wall is IgA produced?

Answer 24

Lamina propria

Question 25

What are the functions of IgA?

Answer 25

Relatively resistant to proteolysis. Neutralises viruses and toxins. Enhances non-specific defense mechanisms (lactoperoxidase, lactoferrin). Inhibits:
bacterial adhesion, macromolecule absorption, inflammatory effects of other Igs.