37) Immunological functions of the alimentary tract Flashcards
1
Q
What are the two types of immunity?
A
- Systemic: Everything that happens in the body (e.g. bone marrow, blood, spleen, thymus or blood)
- Mucosal: Everything that happens outside the body (e.g. eyes, nose, lungs, gut, mouth, genitourinary tract). They are protected by secretions and are wet (covered by a layer of mucus)
2
Q
What is the mucosa surfaces?
A
- Regions within the body that are covered in mucus
- They are not sterile and are colonised by microbes forming microbiomes
- These sites are open to the environment and so are the main route for entry of infectious organisms
- Infections of these areas are local and not systemic
- Microbes find these sites easiest to infect as they are often specialised for absorption
3
Q
What are the different mechanisms of protection?
A
- Innate mechanisms: Non-specific response mechanism (e.g. mucin, peristalsis, antimicrobial peptides and proteins)
- Adaptive mechanism: Specific response mechanism (e.g. mucosal/secretory immune system)
- The mucosal immune system must be able to differentiate between harmful material and harmless material
4
Q
What are the different sources of immune components entering the mouth?
A
- Saliva is a major contributor to protecting the mouth
- Blood gets into the mouth which provides systemic immune response
- Serum (immune) components through the gums as the gums are supplied by blood vessels
5
Q
How are immune systems mounted in the gut?
A
- There are intraepithelial lymphocytes located within the gut
- When a person experiences an ulcer pathogens are able to get into the epithelium where they can interact with white blood cells and get destroyed
- The epithelium is also raised in a mound containing a dense collection of white blood cells (called Payer’s patches)
- On the surface of this mound sits the M-cells and allows substances to flow into the epithelium from the gut
- These patches are able to analyse substances in the gut taking across samples from the gut and look at them immunologically
- Dendritic cells go around and use their arms to extend out into the gut lumen and pick out bacteria and virus and bring them into the epithelium to sample them
6
Q
What is the function of Peyer’s patches?
A
- They are responsible for recognising pathogens and for inducing an immune response locally (where it is located) and elsewhere in the gut too
7
Q
How can the M-cell sample substances in the gut?
A
- It allows the lymphocytes in the Peyer’s patches to get very close to the surface of the gut
- M-cells also pass down substances from the surface and acts as an antigen presenting cell
8
Q
How are M-cells targetted by pathogens?
A
- Particles and macromolecules: They can take up harmful macromolecules such as cholera toxins and latex particles
- Viruses, parasites and bacteria: They can target M-cells directly by using proteins on the surface that can bind to the M-cell allowing them to enter (e.g. HIV, cholera and salmoneylal)
9
Q
What happens when the Peyer’s patch detects pathogens?
A
- The lymphocytes start to get activated and they start to develop in the Peyer’s patch
- Some of the activated lymphocytes migrate out of the Peyer’s patch and move inside the body
- They are taken in the lymphatic drainage and move away from the gut into the mesenteric lymph node
- Here they mature into mature lymphocytes or plasma sites used to produce antibodies
- ## They then move into blood supply and move to mucosal sites only (due to their homing mechanisms)
10
Q
What is the common mucosal immune system?
A
- An induction of an immune response at once site causes an induction of an immune response at another site
11
Q
Why is breast milk useful for babies?
A
- The breast milk are part of the mucosal immune system and contains all the antibodies that the mother has had as an adult
- This provides antibodies and passive immune protection to new born babies
12
Q
What is the structure of serum antibody (IgG)?
A
- It contains 2 heavy chains and 2 light chains
- These chains are held together by disulphide bridges
- The antibody combines to its target through two antigen binding sites
- There is another protein that wraps around the dimerised IgA which is called secretory component which provides protection against degradation
13
Q
What is the structure of secretory antibodies (IgA)?
A
- It contains two IgA molecules that are dimerised by a joining chain
- This allows it to bind to four molecules and so increases the avidity of the antibody
14
Q
How does serum antibody (IgG) produce an immune response?
A
- They bind to antigens at their active sites which ellicits a response (e.g. inflammation, agglutination or recruiting immune cells)
15
Q
How does secretory antibody (IgA) produce an immune response?
A
- They bind to antigens at their binding site which ellicits immune responses better as they bind more strongly
- They can also undergo immune exculsion, intra-cellular neutralisation, virus excretions and interactions with non-specific factors (e.g. lysozymes)
