immune cells and Organs

Question 1

What does Primary lymphoid organs do and what do secondary lymphoid organs do?
Give the secondary lymphoid organs

Answer 1

Primary (thymus, and bone marrow) : lymphocytes are produced- lymphopoiesis.
Secondary: lymphocytes interact with antigens and other lymphocytes
Organs:
-Spleen
-Lymph Nodes
-Mucosal Associated Lymphoid Tissue (MALT)

Question 2

Describe what happens with the lymphocytes?

Answer 2

Both T and B precursor come from heamatopoeitic cells from bone marrow

• mature lymphocytes enter the circulation
• leave and go into secondary lymphoid tissue
• keep circulating until they meet antigen or die

Question 3

What is the general structure of the thymus gland and explain the staining?

Answer 3

Bi-lobed in mammals, located in the thorax. Lobes are divided into lobules by septa- and in each there are cortex and medulla. Cortex contains immature thymocytes and some become mature in the medulla.
It has a capsule. You get darker staining at the peripheries.
You find whirls of fibroblasts called hassall’s corpuscles in humans that give rise to regulatory T lymphocytes( prevent autoimmune and maintain tolerance to self antigens)
Medulla - not very stained.
Cortex- Very stained

Question 4

How does the thymus change during infection?

Answer 4

It doesn’t

Question 5

How does the thymus change with age?

Answer 5

• atrophies with age
• Reduced output of new t cells, so less diverse (OLIGOCLONAL)
• areas of active T cell production are replaced with adipose tissue and thymus size decreases
• more memory cells
• number of T cells stays the same
• total size of the mature T cell pool does not decline substantially with age.

Question 6

Where are white blood cells produced in foetus and adults?

Answer 6

Foetus: white cell also produced in liver and spleen
Adult: mainly the ends of the long bones (most marrow). The marrow becomes less cellular with more fat droplets.

Question 7

What does the red marrow and yellow marrow produce?

Answer 7

Red: produces blood cells
Yellow: fat

Question 8

what does the lymphatic system allow?

Answer 8

• allows all fluid to be drained through the lymph nodes
• it is filtered through the lymph nodes to identify pathogens before it goes into the blood
• allows you to find out whether there is an infections and WHERE it is

Question 9

What are the names of lymphatic vessels that bring lymph to and from the lymph nodes?

Answer 9

Afferent – in; efferent - out

Lymph arrives at the lymph node through several AFFERENT vessels and leaves through one EFFERENT vessel at the hilus.

Question 10

Describe the structure of the lymph node

Answer 10

Within the lymph node there are LOTS of lymphocytes.

• Are round or kidney shaped and have an indentation at the hilus where the blood vessels enter and leave the node.
• Cortex is a B cell area ( on the outside)
• Paracortex is a T cell area
• B lymphocytes aggregate into FOLLICLES

Question 11

What happens during on going immune response

Answer 11

Proliferation of B lymphocytes- GERMINAL center forms which causes lymph nodes to swell

Question 12

What are germinal centers and what do they indicate?

Answer 12

Germinal centers are accumulations of B cells – the germinal centers indicate the presence of on-going infection

Question 13

How do lymphocytes enter and leave the lymph nodes?

Answer 13

• come in the circulation and leave via HIGH ENDOTHELIAL VENULES and enter the lymph.
• move from lymph node-lymphoid vessels- blood via thoracic duct
• directed by chemokines.
• if there is an infection, cells which recognise the infectious agent are held in the lymphoid tissue where they proliferate and differentiate

Question 14

Where do lymphocytes exit the circulation and enter the lymph?

Answer 14

High endothelial venules

Question 15

What is the immunological role of the spleen?

Answer 15

It filters the blood for antigens

Question 16

Describe the organisation of lymphoid tissue around the arteries in the spleen.

Answer 16

White pulp: constitutes the major initiator of responses to blood-borne antigens (viruses).
Made up of Primary follicle, Marginal Zone and Periarterial lymphatic sheath.

Red pulp: general filter for blood.

Red pulp makes most the spleen than the white pulp.

Splenic artery- brings blood in and divides into central arteriole, and is surrounded by lymphoid tissue which contains lymphocytes. This is where the white pulp is.
Around the central arteriole=Pariarterial lymphatic sheath (PALS)
- nearest to arteriole is mainly T area
-Adjacent to PALS is B cell area which is the follicles.
-if there is ongoing immune response you can get germinal centers in the spleen.

Question 17

what type of infections are those without a spleen most susceptible to?

Answer 17

Infections with encapsulated bacteria.

Encapsulated= encapsulated with polysachharide.

Question 18

What is an example of Mucosa Associated Lymphoid Tissue ( aggregates of lymphoid tissue that do not have a tough outer capsule)

Answer 18

Peyer’s patches:
-regions of lymphoid tissue found in the wall of the gut
-Large aggregates of lymphocytes found just below the intestinal epithelium.
-organised into B and T cell areas
-Follicles and Germinal centers (during immune response) can be seen. Mainly B lymphocytes found.
-there are lots of intraepithelial lymphocytes(do not need priming. Upon encountering antigens, they immediately release cytokines and cause killing of infected target cells).
M cells (microfold) in the epithelial layer sample antigens from the gut and deliver antigens to the lymphocytes in the peyers patch.

Question 19

Which immune cells are found in the subcutaneous immune system?

Answer 19

Langerhans cells
-Dendritic cells of skin and mucosa: capture antigens and migrate via lymphatic vessels to draining lymph nodes.
Keratinocytes: detect damage in the skin and secrete signalling molecules to communicate this.
-Tissue resident macrophages
-T Lymphocytes: migrate to the skin if necessary.

Question 20

what type of cells are found in the skin

Answer 20

DENSE network of immune system cells:
Mainly:
Langerhans and intraepidermal lymphocytes.

Question 21

What are the three receptor interactions involved in the extravasation of lymphocytes?

Answer 21

Selectin binding – weak interaction Chemokine receptor on the lymphocyte binds to chemokine on the HEV(high endothelial venules)
Integrins on the lymphocytes bind to ICAM-1.

Question 22

Describe the sequence of events that occur when lymphocytes move out of the circulation.

Answer 22

The lymphocytes are initially rolling along the endothelial layer – selectins bind and slow down the rolling. Then the chemokine receptor on the lymphocyte will bind to the chemokine on the HEV (high endothelial venules). When the chemokine binds, the integrin will be changed to the high affinity state allowing it to bind with ICAM-1
which allows immobilisation of the lymphocytes and allows them to move from the circulation and enter the tissue

Question 23

How do ALL lymphocytes look under a microscope?

Answer 23

-large nucleus and small cytoplasm.

Question 24

What receptors do all T cells have?

Answer 24

CD3

Question 25

What other types of receptor do T cells have?

Answer 25

90% of T cells have alpha-beta receptors and 10% have gamma-delta
Of the alpha-beta receptors:
2/3 have CD4 and 1/3 have CD8

Question 26

What are the two main receptors that all B cells have?

Answer 26

CD19 and CD20

• Express MHC class II
• can present antigens to Helper T cells

Question 27

What are the T cell subsets

Answer 27

CD4+ = T helper cells, regulatory T cells     - these secret cytokines
CD8+ = Cytotoxic T cells- lyse infected cells, secrete cytokines.

Question 28

What are the APC , location and what does it present to?

Answer 28

APC:
Dendritic cells
Follicular dendritic cells
B cells
Activated Macrophages

Location:
Widespread e.g. skin and mucosal tissue; migrate to draining lymph nodes
lymphoid follicles
lymphoid tissue
lymphoid tissue, peripheral tissues

Presents to:
T cells
B cells	
T cells
T cells

Question 29

What is Cluster of

Differentiation (CD)

Answer 29

Developed using monoclonal antibodies, clusters of which recognised the same cell surface antigen.
CD is used as cell markers

Question 30

How big is the human lymph node?

Answer 30

1-15 mm across

Question 31

what type of antigen do T cell and B cell recognise?

What is the antigen receptor in T cells and B cells structure

What CD do T cells and B cells present?

Where are T cells and B cells produced

Answer 31

T cell: Recognize processed antigen presented at the cell surface by MHC molecules
B cell: Recognize intact, free antigen (not presented by MHC molecules)

T cells:Antigen receptor is either αβ or γδ TCR
B cells: Antigen receptor includes cell surface antibody

T cell: All T cell express CD3: T cells express CD4 or CD8, but not both
B cells: Express CD19 and CD20 at surface

T cell: Produced by Thymus
B cell:Produced by Bone Marrow

Question 32

where are B cells made and differentiated?

Answer 32

B cell differentiation is centripetal with the stem cells under the bone and most mature phases of the B cell pathway found nearer the centre of the marrow.