Immunological functions of the alimentary tract Flashcards

1
Q

What are the Divisions of the immune system?

A

Innate and adaptive

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2
Q

What is innate immunity?

A

Prevents infections and avoids disease

Non-specific

No memory

Mediated by:

  • macrophages
  • epithelial barriers
  • secretions
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3
Q

What is adaptive immunity?

A

Responds to infections and prevents disease

Highly specific; response to targeted microbe

Memory (B and T memory cells)

Mediated by:

  • lymphocytes
  • antibodies
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4
Q

Describe the systematic immune response.

A

Protects the entire body

  • Bone marrow
  • Spleen
  • Thymus
  • Lymph system
  • Blood circulation
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5
Q

Describe the mucosal immune system.

A

The immune system that protects internal mucosal surfaces:

  • oral surface
  • nasal surface
  • lacrimal surface
  • GI tract
  • Bronchial tract
  • Genitourinary tract
  • Mammary glands

which are the site of entry for virtually all pathogens and other antigens.

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6
Q

What is the Role of secretions at mucosal membranes?

A

Function to wash away anything that is there

*meaning pathogenic bacteria must try to adhere to these surfaces and not be washed away

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7
Q

What are the Innate mechanisms of mucosal protection?

A
  • Mucin
  • Peristalsis
  • Antimicrobial peptides and proteins e.g. lysozyme, lactoferrin, phagocytes
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8
Q

What are Adaptive mechanisms of mucosal protection mediated by?

A

mediated by antibodies (mucosal/secretory immune system)

  • IgA/IgM
  • IgG
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9
Q

Describe the Sources of Serum, Saliva and Local Antibodies in the Oral Cavity.

A

-Saliva can protect the tooth. Contains enzymes and antibodies and we push that through into our mouths the whole time

-The gingival tissues constantly have a serum exudate going on to the tooth surface
o The exudate is derived from the blood system
- The exudate contains all the blood components apart from RBCs
- It has WBCs, antibodies and lymphocytes

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10
Q

Give the Three primary routes of infection for a pathogen.

A

1) Breach of the epithelium
- e.g. a stomach ulcer

2) Squeezing across epithelial junctions
- passively or via Langerhan cells which will carry the pathogen across

3) Peyer’s Patches
- collection of WBCs in the gut, which is the lymph node of the mucosal immune system and samples what is in the gut lumen through a specialised M cell, with the rest of the Peyer’s patch covered by normal columnar epithelium

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11
Q

Name 3 lymphoid cells.

A

Intra-epithelial lymphocytes

Lymphocytes and macrophages scattered in the lamina propria

Peyer’s patches

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12
Q

What is the M cell?

A

Sits on top of the Peyer’s patch and samples the gut fluid lumen and sends it down to the lymphocyte underneath

*easiest point of entry for pathogens

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13
Q

Describe the Migration of Immune cells from Peyer’s Patches.

A

Once a pathogen gets through to the lymphocytes, it triggers an immune response. A B-lymphocyte will start to mature into a B-cell, as it does this it will migrate away from the Peyer’s patch and drain to the local lymph node (mesenteric lymph node-where they continue to mature) and enter back into the lymph circulation back into the blood circulation.

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14
Q

Describe the process of the Common Mucosal Immune System.

A
  • The WBC picks up the antigen and the WBC matures
    o The WBC travels through the lymph drainage to the mesenteric lymph node
    o It continues its maturation and it travels up through the lymph drainage and gets released into the blood stream
    o It travels through the blood stream, goes back to the gut to provide antibodies
    ♣ However, it also goes to everywhere else in the mucosal immune system

The most interesting thing about a common mucosal immune system is that if you introduce a vaccine to a Peyer’s patch in the gut, you don’t only get a response in the gut, but also in your saliva, breast milk, lacrimal fluid etc.

*encountering an antigen at one mucosal site leads to immunity across all mucosal sites

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15
Q

What are Mucosal antibodies?

A

Predominantly SIgA (secretory IgA)

Found in all secretions and breast milk

Provides passive immune protection in new-born infants

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16
Q

Describe what Serum IgG and Secretory IgA are.

A

Serum IgG composed of light chain and heavy chain.

In mucosal surfaces there is a more complex antibody, with a protein linking two antibodies together. This antibody has the capability to bind to 4 antigens, making it more difficult for pathogens to burrow through the mucosal surface. In this way the mucosal IgA is much better at this surface than serum IgG would be.

17
Q

What is the Secretory component?

A

Another protein wrapped around SIgA to protect the antibody from being degraded by proteolytic enzymes we produce or produced by bacteria.

18
Q

Decribe the Mechanism of Action of IgG.

A
  • Binds key functional sites on microbes and toxins to block functionality.
  • Agglutination of bacteria
  • Induces inflammation by activating complement pathway
  • Recruits immune cells
19
Q

Describe the Mechanism of Action of SIgA.

A
  • Binds key functional sites on microbes and toxins to block functionality.
  • Agglutination of bacteria (better than IgG)
  • Immune exclusion
  • Intracellular neutralisation
  • Virus Excretion
  • Interaction with non specific factors e.g. lysozyme, lactoferrin, peroxidases

*We don’t want to induce inflammation in the gut, so IgA doesn’t induce inflammation or bind/recruit immune cells etc.

20
Q

What is Oral immunisation?

A
  • Attenuated virus (e.g. polio)
  • Attenuated recombinant bacterial mutants (e.g. Salmonella typhi)
  • Mucosal adjuvants (e.g. cholera toxin)
  • Liposomes, microspheres
  • Capsules
  • Transgenic edible plants
21
Q

Describe the process of Oral Vaccine Delivery using GM plants.

A

1) The Hep B surface antigen gene is transferred from yeast into a plant cell
- potato is used as a prototype

2) Potato plants are regenerated from transformed cells
3) Hepatitis vaccine is correctly expressed by potato plants
4) GM potatoes are harvested that contain the hepatitis vaccine

22
Q

Describe the Systemic immune response to vaccination.

A

One injection would produce a small antibody response, taking one or two weeks to develop, then it would die down.

If you then gave a booster injection, it produces a massive response, mediated by IgG and this gives the immunity. It may take years for this antibody response to decline.

23
Q

Describe the Mucosal Immune Response to Vaccination.

A

It appears that mucosal immunity doesn’t have great memory as a second vaccination has an antibody response very similar to the first vaccination and the immunity takes a nosedive.

24
Q

What is Oral tolerance?

A

Oral tolerance is an active process of local and systemic immune unresponsiveness to orally ingested antigens such as food.

*orally ingested antigens can suppress systemic immunity

25
Q

What are the Practical Considerations of Oral Tolerance?

A
  • Tolerance to dietary foods (we do need oral tolerance so we can eat, in people with food allergies this oral tolerance has broken down)
  • Oral vaccination and safety
  • Treatment and prevention of autoimmune diseases
26
Q

Give some factors that cause oral tolerance and how oral vaccinations avoid them.

A

1) Nature of antigen
- Soluble antigens

*Vaccinations= antigens/adjuvants or other formulations

2) Frequency of Delivery
- Repeated sustained doses

*Vaccination= limited number of immunisations given

3) Dose
- High doses

*Vaccination= Low doses