GI immunology Flashcards
List the pattern recognition receptors (PRRs).
Toll-like receptors, NOD-like receptoes, RigI-like receptors, C-type lectins, scavenger receptors
What are PRRs?
Antigen recognition receptors in the innate immune system. Each immune cell carries an identical receptor of a given type.
What are the two main groups of PRRs?
- Cell surface (transmembrane) and intracellular receptors – TLRs, NLRs, RLR’s and CLR’s
- Fluid-phase soluble molecules
What do PRRs respond to?
PAMPs (pathogen-associated molecular patterns) and DAMPs (danger-associated molecular patterns).
What are the central features of the adaptive immune system?
Unique antigen receptor found on each lymphocyte
In response to infection this lymphocyte undergoes clonal expansion
What are the innate components of the GI immune system?
Commensals, epithelial barrier, molecular factors produced by epithelial cells.
What are the adaptive components of the GI immune system?
Gut-associated lymphoid tissue (GALT)
What are M cells?
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.
Name some of the beneficial members of the gut flora?
Lactobacilli and bifidobacterium.
At how many years is the colonic microflora considered to be adult-like?
2 years.
What are prebiotics and what is a good source of these in infancy?
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).
What are probiotics?
Live microorganisms which when administered in adequate amounts confer a health benefit on the host.
What are the benefits of GI microflora?
Resistance to colonisation by pathogens, stimulate local immunity, oral tolerance, nutrition, epithelial cell turnover, intestinal motility.
What are the hazards of GI microflora?
Around 15% pathogenic bacteria. Extraintestinal disease; septicaemia, autoimmunity; reactive arthritis
Allergy
What is eubiosis?
A state on balance in the GI microflora.
What is dysbiosis?
A state of imbalance in the GI microflora.
How does the epithelial barrier contribute to GI immunology?
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.
How do goblet cells contribute to GI immunology?
Produce mucins to provide for mucus layers that resist microbial access
How do enterocytes contribute to GI immunology?
Produce antimicrobial peptides (defensins, lysozyme, lactoferrin, cathelicidins).
Mechanical action.
Which class of Ig is secreted by the gastric mucosa?
IgA
What are mucosal follicles?
Organised mucosal associated lymphoid tissue. Aggregate in Peyer’s patches or exist as single follicles.
What proportion of intraepithelial lymphocytes are T cells?
90%
What are the two main types of lymphocytes associated with the gut?
Intraepithelial lymphocytes (CD8) and Lamina Propria lymphocytes (CD4).
In which layer of the gut wall is IgA produced?
Lamina propria
What are the functions of IgA?
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.
