M: Adaptive immunity 1 - Week 4

Question 1

List 3 innate defences to infection found at the ocular surface of they eye

Answer 1

1. Lids, tears: wash away microbes, inhibit growth
2. Complement: lyses bacteria and enveloped viruses; attracts phagocytes
3. Tissue macrophages + Neutrophils: phagocytose microbial survivors

Question 2

Where on the ocular surfaces is complement found?

Answer 2

in tears and conjunctival tissue

Question 3

What happens to the level of tissue macrophages and neutrophils when lids are closed?

Answer 3

Increases

Question 4

List 3 innate defences to infection found at the anterior chamber of the eye

Answer 4

1. Structure itself: prevents microbe access
2. Complement: lyses bacteria and enveloped viruses
3. innate immune system: activated by PAMPs

Question 5

How much does the anterior chamber of the eye rely on physical and soluble mediators to prevent infection? Why is this the case?

Answer 5

Heavy reliance on physical and soluble mediators because a cellular response would impair vision

Question 6

How can organisms overcome the innate defences of the eye? (3)

Answer 6

1. they gain access to anterior chamber via trauma or blood
2. they have specific adhesins for the ocular surface
3. they can overcome the innate immune system

Question 7

In regards to lymphocytes:
A) What immune system are they involved in?
B) Name the 2 types of lymphocytes
C) What are lymphocytes derived from?
D) What do lymphocytes recognise?
E) Where are the 2 types of lymphocytes derived?

Answer 7

A: Adaptive 
B: B and T lymphocytes
C: Haemopoietic stem cells
D: Antigen
E: B lymophocytes = bursa. T-lymphocytes = thymus derived

Question 8

How do the 2 types of lymphocytes bind antigen?

Answer 8

B-lymphocytes: Binds whole antigen

T-lymphocytes: Receptor binds antigen peptide displayed on Antigen Presenting Cells

Question 9

How many different antigens can a lymphocyte recognise?

Answer 9

A lymphocyte has multiple copies of a unique receptor only, which means that a single lymphocyte can only recognise a single unique antigen.

However, it has multiple receptors for this antigen and can bind to multiple of this particular antigen

Question 10

How and where are T and B cell receptors generated?

Answer 10

By random somatic gene rearrangements during differentiation in the primary lymphoid tissues (Bone marrow/Bursa for B cells and Thymus for T cells)

Question 11

When can T ad B cells leave the primary lymphoid tissues after differentiation?

Answer 11

When these cells express receptors for non-self antigens

If they express receptors for self antigens, they are destroyed

Question 12

Where in the primary lymphoid organs do lymphocytes develop? (3)

Answer 12

• foetal liver
• bone marrow
• thymus

Question 13

What happens once a lymphocyte is released from the primary lymphoid organ?

Answer 13

Is released as a “Naive lymphocyte” as it hasn’t encountered antigen. It travels to our bloodstream and then either enters the spleen or back into the lymph node, an then travels back to the bloodstream.

It does this until they’ve encountered antigen (in the lymph node or spleen).

Once encountered antigen, the “Activated lymphocytes” travel back to the bloodstream and then start entering the tissues and then circulate between the tissues and bloodstream

Question 14

Where do naive lymphocytes first interact with foreign antigens? (3)

Answer 14

In the secondary lymphoid organs:

• spleen
• lymph nodes
• molecular associated lymphoid tissues (MALT)

Question 15

List the 7 lymphoid tissues of the adaptive immune system in the body

Answer 15

1. conjunctival associated lymphoid tissue
2. adenoid
3. tonsil
4. lymph node
5. spleen
6. appendix
7. large intestine

Question 16

Where can you find the 3 eye-associated lymphoid tissues?

Answer 16

1. lacrimal gland
2. lacrimal drainage system
3. conjunctiva

Question 17

How are lymphocytes spread in the conjunctiva?

Answer 17

Diffusely spread among the cells of the conjunctiva. Found in “follicles”

Question 18

What name do we often use to refer to the tissues and structures associated with our mucosal tissue?

Answer 18

Common Mucosal Immune System

Question 19

True/False: There are lymph vessels that drain from the conjunctiva

Answer 19

True

Question 20

True/False: There aren’t any lymph nodes that drain from the eye and anterior chamber

Answer 20

True

Question 21

Where do a lot of the antigens present in the ocular departments drain to? What does this mean?

Answer 21

Drain to the spleen. Therefor a lot of immune responses are actually induced in the spleen

Question 22

Describe the vascularity of the central cornea. Where in the cornea are dendritic cells present?

Answer 22

The central cornea is avascular. Dendritic cells are present only in the peripheral corneal epithelium

Question 23

Is there any lymphatic drainage in the cornea? Explain

Answer 23

No lymphatic drainage. Most of the dendritic cell antigens from the cornea are drained through the blood and delivered to the spleen

Question 24

Why are immune responses in the intraocular compartment of the cornea often suppressed?

Answer 24

Because otherwise the immune activation would damage/impair our vision

Question 25

What do B-lymphocytes mature into and what do they produce? How are they important?

Answer 25

B-lymphocytes mature into plasma cells (mature B cells) that produce antibodies, which are important in controlling and removing extracellular pathogens

Question 26

Why can’t antibodies remove intracellular pathogens?

Answer 26

Because they cannot penetrate into cells (they are too big)

Question 27

What chains do antibodies consist of? (2)

Answer 27

• 2 identical heavy chains, and

- 2 identical light chains

Question 28

What 2 distinct regions do antibodies have? How many forms can these 2 regions take

Answer 28

• Fc (constant region): can take 5 forms/isotypes

- Fab (variable/antigen-binding region): can take an almost infinite variety of forms

Question 29

Where in the Fab region of the antibody does the antigen bind?

Answer 29

Binds in the “pocket” of the heavy and light chain

• this pocket is generated from random rearrangements that happen when the B cell undergoes maturation

Question 30

How many possible antigen binding sites can be generated in B cell maturation? What does this mean?

Answer 30

Around 10 to the power of 11. In other words we can make 10^11 different antibodies

Question 31

When is a B-lymphocyte unable to change its Fab region? Can it still change Fc region in this circumstance?

Answer 31

Once the B cell is expressing a functional antibody and uses that antibody as the receptor for a particular antigen, it cannot change Fab anymore. However it can still change Fc.

Question 32

If B cells in the bone marrow bind to self antigen, what happens?

Answer 32

They get deleted

Question 33

What causes different B cells to make different antibodies?

Answer 33

Differences in the variable region (Fab) that binds specific antigen

Question 34

What are the 5 antibody isotypes? What determines the isotypes?

Answer 34

Determined by the constant region (Fc) of the heavy chain:

- IgM, IgG, IgA, IgD, IgE

Question 35

How do phagocytes recognise the Fc region of antibodies?

Answer 35

They have Fc receptors that recognise the Fc region of the antibodies

• Fc receptor (FcR) that binds an IgG antibody = Fc y receptor
• Fc receptor (FcR) that binds an IgE antibody = Fc alpha receptor

Question 36

What 2 things does the Fc region of an antibody bind?

Answer 36

• phagocytic receptors

- complement proteins

Question 37

How do antibodies control extracellular pathogens? Consider the isotypes (5)

Answer 37

They:

1. Prevent pathogen binding at mucosal surfaces (IgA)
2. Neutralize the action of toxins (IgA, IgG, IgM)
3. “Opsonise”: The Fc region binds directly to Fc receptors on phagocytes (IgG)
4. Trigger the complement cascade (IgG, IgM)
5. Induce release of cytotoxic products from macrophages and NK cells (by IgG binding FcyR) and eosinophils (by IgE binding FceR)

Question 38

Explain how antibodies outside the mucosal tissue protect from invasion

Answer 38

• viruses, bacteria and toxins are trying to invade the tissues
• antibodies such as IgA are secreted across the epithelial cells/mucosal surface
• IgA binds to the bacteria, toxins and viral pathogens, this prevents them from binding the mucosal surface (i.e. epithelial cells)

Question 39

Explain how antibodies inside the mucosal tissue protect from microbial invasion via phagocytosis

Answer 39

• microorganisms that cross the mucosa into the tissue
• may be coated with IgG, which can then bind to the FCy receptor on a macrophage
• This induces phagocytosis and killing through the recruitment of lysosomal proteins

Question 40

Explain how antibodies inside the mucosal tissue protect from microbial invasion via complement cascade

Answer 40

• bacteria coated with either IgG or IgM molecules can activate the cascade
• results in opsonisation of the bacteria and phagocytosis/lysis of the bacteria

Question 41

Explain how antibodies inside the mucosal tissue protect from intracellular infection with viruses

Answer 41

• infected host cells will display viral proteins on their surface
• viral proteins bind to IgG, which can activate complement cascade or the NK cells

Question 42

Explain how antibodies inside the mucosal tissue protect from parasitic infections

Answer 42

1. IgE responses are important in protection against parasite
2. IgE binds to the parasite or antigen on parasite
3. Once bound, the IgE will bind to the FceR on the eosinophil and activate it