W2 Mucosal Immunity

Question 1

What is the structural difference between spleen, lymph nodes and MALTS organs?
Why is this important clinically?

Answer 1

MALTS are non capsulated meaning they are not surrounded by a dense layer of connectives tissue, the cells of MALT is continuous with normal cells within the tissue.
Lymph nodes and the speen are capsulated meaning they have a connective tissue around their outside.
This is important clinically because capsulated organs can be surgically removed, MALT can not be removed separate to other tissue

Question 2

What is the function of the capsule around the lymph nodes?

Answer 2

Controls what can come in and out.
Keeps things trapped inside
Makes an isolated compartment.

Question 3

What is the mesenteric lymph node?

Answer 3

A long lymph node that runs the length of the gut.

Question 4

Give an overview of the function of the spleen in immunology.

Answer 4

Spleen filters blood (not lymph) for antigens
Blood and lymphocytes enter the spleen by the splenic artery.
More lymphocytes flow through the spleen than all lymph nodes combined
Spleen responded to systemic infections.

Question 5

What is the splenic hilus?

Answer 5

The area of the spleen where vasculature, enters/leaves.

Question 6

Describe the main internal structure of the spleen.

Answer 6

Has an outside capsule that extend inwards to make barriers called trabecula.
Has an outer red pulp area.
Then an inner white pulp area, this consists of primary follicles, germination centres and pariarteriolar lymphoid sheath.
The area between the white pulp and the red pulp is the marginal zone.

Question 7

What is the function of red pulp in the spleen?

Answer 7

Contains many macrophages and red blood cells (very few lymphocytes)
Macrophages phagocytose damaged or dead RBC.

Question 8

What is the function of white pulp in the spleen?

Answer 8

Mainly surrounds arteries in the spleen forming PALS.
Mainly populated by t-lymphocytes, which are activated by dendritic cells from within the marginal area of the spleen migrating through once activated.

Question 9

What is PALS?

Answer 9

Periarteriolar lymphoid sheath region of (mainly mature ) t lymphocytes surrounding the central arteries in the spleen, part of the white pulp area.

Question 10

What is the marginal zone of the spleen like?

Answer 10

Found at the edge of PALS, is mainly made of b-lymphocytes and contains primary lymphoid follicles.

Question 11

Explain the processes by which an immune response in the spleen is activated.

Answer 11

Foreign antigens is carried into the spleen in the blood from the splenic artery.
The antigen is captured by dendritic cells in the marginal zone
Dendritic cells move to the PALS, where it activated the specific t-helper cell.
Helper t cell activates the specific b cell, both move to the primary follicles in the marginal zone
This interaction leads to the production of a secondary follice with a germinal centre.

Question 12

Give an overview of the structure and function of the lymph nodes.

Answer 12

Clustered at lymphatic junctions, filter lymph for antigens either free antigens or as APC.
Contain lymphocytes, macrophages and dendritic cells.
Have a mesh-like reticular framework

Question 13

Why do lymph nodes enlarge when undergoing an immune response?

Answer 13

Antigen detected, an immune response occurs.
The single efferent vessels contain a high amount of antibodies and lymphocytes from clonal selection and affinity maturation.

Question 14

Explain the process by which an immune response may be activated within a lymph node.

Answer 14

free antigens or PAPC enter the lymph node in the lymph.
Free antigens are processed in the paracortex by dendritic cells.
PAPC (b-cell or dendtiric cell) active the specific helper t cell.
B-cells and T-cell migrate to primary follicles of the cortex, may interact with follicular dendritic cells.
Forms a secondary lymphoid follicle with a germinal centre.

Question 15

What are lymphoid follicles?

Answer 15

A collection of lymphocytes and dendritic cells.
Primary follicles are mainly inactive b-cells
Secondary follicles, contain a germinal centre where activated b-cells are rapidly proliferating.

Question 16

Explain the structure of primary and secondary lymphoid follicles?

Answer 16

All follicles have an outer mantle zone, within the follicle there is a b-cell and a t-cell zone (mostly b cell). Inactivated cells with no germinal centre.
In a secondary follice, an active t-helper cell will come in contact with the specific b cell, causes rapid proliferation and formation of a germinal centre within the b-cell zone.

Question 17

What are germinal centres?

Answer 17

Specialised microenvironment within secondary lymphoid follicles, where activated B-cells proliferate rapidly and undergo somatic hypermutation.
Inactive b-cells are pushed to the edge of the b-cell zone.
The b-cells are surrounded by a cuff of helper t-cells.

Question 18

Explain the processes that occur within a secondary lymphoid follicle.

Answer 18

Naive b cell passess through the mantle zone, naive b cells comes into contact with antigen and is activated by a specific t helper cell.
Activated b-cell within the follicle undergoes cloncal expansion and somatic hypermutation.
Plasma cells and memory b-cells leave the follicle.

Question 19

What happens during somatic hypermutation?

Answer 19

Occurs in active and proliferating b-cells.
Recombination/point mutation of genes involved in producing antibody/ BCR creates a wider variation of receptor variable region (NOT CONSTANT).
Receptors with a new higher affinity for binding is kept alive.
Receptors with a new lower affinity for binding are killed by apoptosis.
Creates higher affinity b-cells leading to more rapid activation of plasma and memory cells.

Question 20

What is class switching in immunobiology?

Answer 20

The process by which an activated b-cell, changes the specific types of antibody it produces from IgM to another to better suit its function.

Question 21

How do lymphatic follicles appear under a microscope?

Answer 21

Dark areas - germinal centre, rapid proliferation means high density of b-cells, less light able to pass through.
Light areas - differentiated b-cells or inactive lymphocytes, may also contain dendritic cells.

Question 22

What is affinity maturation?

Answer 22

Somatic hypermutation is/has occured, b-cells with greater affinity are selected for by specific helper t-cells within the follicle (binding to processed antigen on the b-cell surface), leads to selection of more higher affinity, lower affinity cells die by apoptosis.

Question 23

What happens to long lived plasma cells?

Answer 23

May return to bone marrow.
Release low level high affinity antibody for specific pathogen.

Question 24

What signal do b-cells receive in the light area of the secondary lymphoid follicle?

Answer 24

Signal from specific activated helper t-cell, what type of antibody to produce, how to differentiate.

Question 25

What is an Fc receptor?

Answer 25

A receptor found on the surface of cells (self or non-self) that binds to the constant region of an antibody, allows the antibody to carry out its function.

Question 26

What does the variable region and the constant region of an antibody each determine?

Answer 26

Constant region - class of antibody
Variable region - specificity of antibody.

Question 27

What is the deal with an IgM antibody?

Answer 27

Produced first by b-cell before knows what type of antibody to produce.
Consists of five antibodies hence ten binding sites in a circle,
Constant regions are in the centre, not able to bind to anything.
Often produced before efficient somatic hypermutation
Aid agglutination.

Question 28

What is the functional outcomes of a IgG antibody?

Answer 28

Neutralise toxins
Osponisation
Activate the complement pathway.

Question 29

What antibody types play the most important role in MALT?

Answer 29

IgA and IgD

Question 30

Where is MALT tissue found?
What are the two different types?
What is its function?

Answer 30

Mainly associated with the ileum of the digestive tract as Peyers patches.
Is called GALTS in the gut
is called BALTS in the bronchus.
Found in body areas that open by a tube like structure to the outside world.
Defends against pathogens which have entered by the mucous membranes. Contains large amounts of plasma b-cells.

Question 31

Where are immune defenses in the gut found, related to histological layer?

Answer 31

MALTS - mucosa or submucosa
Goblet cells - epithelium
Cytotoxic T-cells and plasma cells secreting IgA and IgD - lamina propia.

Question 32

What are defensins?

Answer 32

Antimicrobial peptides found in the mucosal layer.
Disrupt cell membranes and virus envelopes

Question 33

Give some examples of GALTs?

Answer 33

Tonsils
Adenoids
Peyers Patches (ileum)
Isolated lymphoid follicles
Appendix

Question 34

What lymph node do GALTs support?

Answer 34

The mesenteric lymph node.

Question 35

Give an overview of the tonsils role in the immune system,

Answer 35

Are GALTS
Have nasopharyngeal, palatine and linguinal tonsils
Form a ring
Have a reticular structure containing macrophages, granulocytes, mast cells and lymphoid follicles.
Defend against pathogens entering the oral or nasal cavity,

Question 36

What are the different sites on MALTS?
What is the function of each site?

Answer 36

Inductive sites - where B and T cells are primed by antigen and differentiate into effector cells.
Effector sites - Where activated B and T cells migrate to carry out there immune function to clear pathogens.

Question 37

How is the epithelium above MALT tissue specialised?

Answer 37

Has microfold cells.
Occur above induction sites in MALTs
Have large invaginations in basal membrane filled with lymphocytes and macrophages and dendritic cells.
Microfold cells phagocytose antigen and release it into the pocket containing dendritic cells leading to their activation.