Immunological Functions of Alimentary Tract Flashcards
List some characteristics of the innate immune system.
- prevents infection and avoids disease
- non-specific
- no memory
- mediated by macrophages, epithelial barriers etc.
List some characteristics of the adaptive immune system
- responds to infection and prevents disease
- highly specific response to targeted microbes
- has memory
- mediated by lymphocytes, antibodies, etc.
Where can systemic immunity be found?
Bone marrow, lymph system, blood circulation
Where can mucosal immunity be found?
Mucous membranes - eyes, nose, mouth, lungs, gut, genitourinary tract
Describe the surfaces of the mucosal immune system and how they can be used by pathogens.
- Covers all the mucosal surfaces (e.g.GI tract, bronchial tract, genito-urinary tract etc.).
- Sites are normally colonised by microbes.
- Main route of entry for pathogens.
The mucosal immune system has innate and adaptive mechanisms.
Expand on these mechanisms.
INNATE - Peristalsis, antimicrobial peptides and proteins (e.g., lysozymes, lactoferrin, phagocytes).
ADAPTIVE - Mucosal/secretory immune system
There are different ways in which pathogens can get across gut surfaces.
List 3 of them.
- Sublamina if there are epithelial breaches
Langerhans cells have extensions to ‘sample’ what’s in the lumen of the gut. The pathogen can adhere to it, and be brought in when the cell moves off. - Peyer’s Patches. The patches are actively sampling the gut via M-cells.
How do M-cells work?
- Sits on top of the epithelial layer
- Samples the gut fluid lumen
- Sends it down to the lymphocytes underneath.
Tests were done showing the antibody response of Peyer’s patches.
What do the tests tell us?
- In order to generate an immune response, the immunogen has to be taken up by the Peyer’s patch.
- Antibodies produced are not limited to just that one site.
List some M-cell targets for uptake.
- particles and macromolecules
- viruses
- parasites
- bacteria
Describe the migration of immune cells from Peyer’s patches.
- Once a pathogen gets through to the lymphocytes, an immune response is triggered.
- B-lymphocyte will start to mature into a B-cell.
- Migrate from the patch to the local lymph node, then re-enter circulation.
Describe mucosal antibodies.
- predominantly SIgA
- found in all secretions and breast milk
- provide passive immune protection in new-born infants
What do mucosal antibodies do instead of going into circulation?
- Home back to the mucosal immune system, back to the gut (and the surrounding gut). - Home to other mucosal surfaces.
Describe the idea of common mucosal immunity.
- Encounter antigen at one mucosal site leading to immunity across all mucosal sites
- Lymphocytes have to home to a secretory gland before they can start producing antibodies.
Describe the two additional components in SIgA antibodies.
- SIgA is dimerised by a joining protein, so can bind to 4 antigens
- Has a secretory component that protects it from being degraded by proteolytic enzymes.
Describe the mechanism of action of the antibodies.
- Bind to key functional sites on microbes and toxins
- Agglutinate
- Induce inflammation
- Recruit immune cells
What does SIgA not do? Give a reason.
- Doesn’t induce inflammation and recruit immune cells
- Avoid inflammation of gut
List some approaches to oral immunisation.
- attenuated virus (e.g. polio)
- attenuated recombinant bacterial mutants (e.g. salmonella typhi)
- mucosal adjuvants [make the vaccine work better] (e.g. cholera toxin)
- liposomes
How would you test the concept of oral vaccine production in plants?
- Grow plants that express hepatitis vaccine to maturity
- Harvest the edible tissue.
- Feed uncooked tubers to animals or humans
- Analyse the immune response.
Describe oral vaccine delivery using GM plants.
- The Hep B surface antigen is transferred from yeast into a plant cell
- Plants are regenerated from transformed cells.
- Hepatitis vaccine is correctly expressed by plants.
- Plants are harvested that contain the hepatitis vaccine.
What is an obstacle with mucosal immunity (oral tolerance)?
If an antigen is first encountered through the mucosal immune system, the systemic immune system may become unresponsive to that antigen.
How is oral tolerance helpful?
- Need to have tolerance to food, otherwise, will cause food allergy
What does the gut do to prevent colonization?
- Peristaltic waves are always moving material through the gut
- Bacteria do not have a chance to colonize bacteria.
What must the adaptive immune system do?
Discriminate between harmful pathogens and harmless antigens
What does the immunological mucosal barrier produce?
Secretory IgA
What are the lymphoid tissues in the gut ?
→Intraepithelial lymphocytes
→Peyer’s patches
What is the gut lined with and why?
Columnar epithelial cells
What is under the epithelial cells?
Submucosal layers
What is underneath the mucosal layers?
Blood vessels and lymph nodes.
What is a Peyer’s patch ?
→It is the lymph node of the mucosal immune system
Why is mucosal immunity not given as a vaccine?
The response is not long-lasting
