11 Immunology Flashcards
Q: How does the microbiota vary at different points in the GI tract? (4)
A: Loads in the mouth is because we put lots of dirty things into it, including food, fluid, cutlery, air etc.
Into the stomach, the low pH kills lots of bacterial populations (except H. pylori).
The number is kept low in the duodenum, jejunum and proximal ileum because of paneth cells and Peyer’s patches (discussed in detail later).
Beyond the ileocaecal valve the number of microorganisms increases markedly.
Q: What are the gastrointestinal mucosa’s four main mechanisms for protection from infection?
A: Physical barriers:
Chemical barriers:
Bacteria protection:
Immunological:
Q: How can the gastrointestinal’s mucosa act as a physcial barrier to protect against infection? (5)
A: a tight epithelial wall, glycocalyx, mucous and unstirred layer. Also, persitalsis to keep things moving along the GI tract
Q: How can the gastrointestinal’s mucosa act as a chemical barrier to protect against infection? (2)
A: bacteriacidal enzymes from paneth cells, and acid from stomach
Q: How does the gastrointestinal’s mucosa act as a barrier to protect against infection in terms of bacterial protection? (2)
A: commensal bacteria maintain immune system priming and may attack foreign species.
Q: How does the gastrointestinal’s mucosa act as a barrier to protect against infection in terms of immunological protection? (3)
A: Mucosa-associated lymphoid tissue (MALT) rich in T cells and B cells, whose components can be further categorised into GALT (Gut-associated lymphoid tissue), BALT (Bronchus-associated lymphoid tissue) etc.
Q: What is GALT? What are the 2 categories of it based on? Describe each and describe 2 examples for each.
A: Gut-associated lymphoid tissue
two categories depending on organisation
- organised sites of lymphoid tissue such as Peyer’s patches in the small intestine and lymphocytes in mesenteria lymph nodules (i.e. where the lymph from the villi drain)
- disorganised sites which include lymphocytes in the lamina propria (mainly IgA-secreting B-cells) and lymphocytes in the interstitial space below the basolateral membrane of the epithelium (called intra-epithelial cells)
Q: Apart from GALT, what other immunological structures are there to protect against infection in the GI tract? function?
A: although not technically GALT, there are Kuppfer cells in the liver which can phagocytose bacteria
Q: What do peyer’s patches consist of? Where are they found? highest concentration where?
A: aggregated lymphoid follicles covered with follicle associated epithelium (FAE)
small intestine, having highest concentration in the distal ileum
Q: What is the function of peyer’s patches? capable of? (2)
What are peyer’s patches rich in? (4)
A: function as “immune sensors” since they are capable of monitoring local bacteria, and provide protection against pathogenic bacteria
B cells, T cells, macrophages and dendritic cells
Q: What does the development of peyer’s patches require? How many do we have by the last trimester of gestation? When do we reach our maximum number? how many is this?
A: requires exposure to bacterial flora (i.e. they are barely present in animal models that are born and reared in sterile environments)
Humans have about 50 by the last trimester of gestation, and hit the maximum of about 250 by their teenage years.
Q: What is FAE? where is it found? What does FAE consist of?
A: follicle associated epithelium (FAE)
- covering aggregated lymphoid follicles of peyer’s patches
FAE contains specialized enterocytes or M cells where enterocytes are just intestinal absorptive cells = simple columnar epithelial cells found in the small intestine
Q: Where are M cells found? Main function? What do they express? aids?
A: follicle associated epithelium (FAE)
- covering aggregated lymphoid follicles of peyer’s patches
main function of M cells is to perform transcytosis of luminal bacteria, antigens and proteins
(uptake and transport of antigens from the gut lumen
to the underlying mucosal immune system)
M cells express IgA receptors, facilitating transfer of IgA-bacteria complex into the peyer’s patches
Q: Antigen uptake in peyer’s patches is a combined effort by? (2) Describe (5).
A: specialised M-cells and dendritic cells
- M cells express IgA receptors, facilitating transfer of IgA-bacteria complex into the peyer’s patches
- these antigens are then presented to the lymphocytes
- for assessment and potential immunological response
- Activated cells develop gut homing markers (follows idea that where immune cells are activated= best place for them to act)
- and migrate to mesenteric lymph nodes for proliferation
Q: What are the M cells an ideal entry point for? eg? Why? (2) Summarise.
A: potential pathogens eg Vibrio cholerae
- accessibility of M cells on the mucosal surface
- ability to transcytose particulate material
M cells can transport a diverse array of mucosal microorganisms across the intestinal epithelial barrier
