gut immunology Flashcards
what is the surface area of the GI tract?
200m^2
what antigen load does the gut have to deal with?
massive antigen load: resident micbrobiota 10^14 bacteria
dietary antigens
exposure to antigens
in terms of immunology what term is used to describe the state of activation of the gut?
what does this mean
restrained activation -
dual immunological role of tolerance vs active immune response
what does the Immune homeostasis of gut & development of healthy immune system require?
presence of bacterial microbiota
what does the gut show a tolerance of vs an active immune response?
tolerance of food antigens and commensal bacteria
immunoreactivity to pathogens
what are the four major phyla of bacteria in the gut? BFAP
Bacteroidetes, Firmicutes, Actinobacteria, Proteobacteria
what does the massive amount of gut microbiota provide?
Provide traits we have not had to evolve on our own - Genes in gut flora 100 times our own genome.
what does dysbiosis describe?
microbial imbalance that disturbs microbial composition e.g. pathogens
what trend is seen in the number of bacterial cell numbers as you move along the GI tract?
why?
increases as you move along.
inhibiting factors such as acids and digestive enzymes limit the number of bacteria, these are not found in the colon
what host factors influence bacterial cell numbers?
nutrients provide growth
digestive factors, peristalsis and defecation cause lysis and elimination
what type of bacteria causes regulation, which causes inflammation?
symbionts regulate - present with no benefit or harm from host or bacteria
pathobionts inflame - cause dysregulation
what are commensal bacteria?
organisms that benefit from host but have no effect on host
what are the causes of dysbiosis?
infection and inflammation
diet
xenobiotics
hygiene
genetics
what are xenobiotics?
small chemical compounds that enter the gut unnaturally e.g drugs or pollutants
what physical barriers in the gut provide mucosal defence?
epithelial barrier
peristalsis
enzymes
acidic pH
commensal bacteria occupy _________
an ecological niche
what are the immunological mucosal defence mechanisms of the gut following invasion?
MALT (Mucosa Associated Lymphoid Tissue)
GALT (Gut Associated Lymphoid Tissue)
what epithelial barriers provide mucosal defence in the gut?
Mucus layer - Goblet cells
Epithelial monolayer - Tight junctions
Paneth Cells (small intestine)
Bases of crypts of Lieberkühn.
Secrete antimicrobial peptides (defensins) & lysozyme.
where is MALT found?
MALT - mucosal associated lymphoid tissue is Found in the submucosa below the epithelium, as lymphoid mass containing lymphoid follicles
in MALT, what are the lymphoid follicles surrounded by and what does this allow for?
Follicles are surrounded by HEV postcapillary venules, allowing easy passage of lymphocytes
what is GALT responsible for?
Responsible for both adaptive & innate immune responses
what immune cells are found in the gut associated lymphoid tissue?
Consists of B & T lymphocytes, macrophages, APC (dendritic cells), and specific epithelial & intra-epithelial lymphocytes
what are the two types of GALT?
non-organised and organised
what are the two types of non-organised GALT?
Intra-epithelial lymphocytes
Make up 1/5th of intestinal epithelium, e.g. T-cells, NK cells
Lamina propria lymphocytes
what are the four types of organised GALT?
Peyer’s patches (small intestine)
Caecal patches (large intestine)
Isolated lymphoid follicles
Mesenteric lymph nodes (encapsulated)