Immunology 2- Immune cells and organ

Question 1

What is the role of primary lymphoid organs

Answer 1

are where lymphocytes are produced:

Lymphopoiesis

Question 2

What is the role of second lymphoid organs

Answer 2

where lymphocytes can interact with antigen and with other lymphocytes

eg

spleen
lymph nodes
mucosal associated lymphoid tissues (MALT)

Question 3

Describe the thymus

Answer 3

Located below the thyroid gland

It is bi-lobed

Microscopic analysis of a stained section shows lobules within the lobes which are packed with lymphocytes.

Question 4

What are HASSALL’S CORPUSCLES

Answer 4

you get whirls of fibroblasts where regulatory T lymphocytes develop.

Question 5

What happens to the thymus output with ages

Answer 5

T cell production declines with age

YOUNG - HIGH output of new T cells with new specificities

As you age…. - reduced output of new T cells - more fatty tissue in the thymus - size of the thymus DECREASES

Question 6

What is the difference in T-cell in older people

Answer 6

The total number stays the same

LESS DIVERSE repertoire of T cells

More memory cells

They become OLIGOCLONAL - less diverse

So if an elderly person is exposed to a new infection, they are less likely to produce an efficient T cell response because they won’t be producing as many new T cells.

Question 7

What happens in the bone marrow

Where is bone marrow produced in the feotus and adults

What does red and yellow marrow produce

Answer 7

Site of Haematopoiesis

Increased white cell production during infection

Foetus - these cells are also produced in the liver and spleen

Adults - mainly the ends of the long bones where you find most of the marrow - the marrow becomes less cellular with more fat droplets

During an acute phase response - more white blood cells are being produced by the bone marrow to try and combat infection.

RED MARROW - produces blood cells

YELLOW MARROW - fat

Question 8

What is the arrangement of lymphocytes in lymph nodes

Answer 8

B cell areas tend to be on the outside

B lymphocytes aggregate into FOLLICLES

T lymphocytes on the inside

Question 9

What happens during an immune response

Answer 9

On going immune response - PROLIFERATION of B lymphocytes - GERMINAL CENTER forms

Germinal Center - lymphocytes are rapidly proliferating to produce antibodies against the pathogen which caused the infection.

Question 10

How do lymphocytes enter and leave the lymp nodes

Answer 10

endothelial venules

They are directed by CHEMOKINES

Question 11

What is the role of the spleen

Answer 11

Filter for antigens IN THE BLOOD

Question 12

How is brought blood into the spleen

Where are b cells and t cells located in the spleen

Answer 12

Splenic Artery brings the blood in and is surrounded by lymphocytes.

The area absolutely adjacent to the arteries is the periarterial lymphatic sheath (PALS) - mainly a T cell area

Adjacent to that is the b cell area

Question 13

Why is the epithelium an effective first line of defence

Answer 13

Mucosae + Skin = physical barrier

Large surface area + in many places, single layer of cells —-> heavily defended by the immune system

MALT (mucosa-associated lymphoid tissue) and the cutaneous immune system are at these places

Question 14

In regards to gut associated lymphoid tissues

what is the peyers patch

What do m cells do

Answer 14

PEYER’S PATCH - large aggregates of lymphocytes

M Cells (microfold) - samples antigens from the gut and deliver antigens to the lymphocytes in the Peyer’s patch

Question 15

The Cutaneous Immune System (4)

Answer 15

LANGERHANS CELLS - dendritic cells of the skin and mucosa
Capture antigens in their local environment
Migrate via lymphatic vessels to draining lymph nodes
Lymphocytes are also present

Keratinocytes are good at detecting damage in the skin and secrete signalling molecules to communicate this knowledge of damage.

Dermis - you get tissue-resident macrophages

T lymphocytes circulate and can migrate to the skin if necessary

Question 16

What are High Endothelial Venules (HEV)

Answer 16

a specialised endothelium with a number of molecules involved in arresting the lymphocyte. Once it has been immobilised in the correct place, it can move in through the membrane.

When the chemokine receptor on the lymphocyte binds to the chemokine on the HEV, the Integrin becomes the high affinity binding form.

Question 17

Describe the extravasation of Naïve T Lymphocytes into Lymph Nodes

Answer 17

Intially binds with selectins=weak

Then interacts with chemokines on the HEV

This changes the affinity for intergrin ( a receptor) to a high affinity

Integrin can then bind to its ligand - ICAM-1 (Intracellular adhesion molecule 1)

The lymphocyte then becomes immobilised and can move into the tissue

Question 18

Describe lymphocytes

Answer 18

Small cells with agranular cytoplasm and a large nucleus

Can be subdivided into 2 groups depending on where they were produced 
B lymphocytes (Bone Marrow)
T lymphocytes (Thymus)

Question 19

How many t cells do we have

Answer 19

50 x 7.5 x 109 = 3.75 x 10^11

Question 20

What is the marker on all t-lymphocytes

Answer 20

All express CD3

There are two groups of TCR:

ab - 90% in blood
CD4 - 2/3
CD4+ = T Helper Cells, Regulatory T Cells - these secrete cytokines

CD8 - 1/3
CD8+ = Cytotoxic T Cells - lyse infected cells, secrete cytokines

gd - 10% in blood

Question 21

T Cell Antigen Recognition

Answer 21

Only recognise PROCESSED ANTIGENS

Recognised by the TCR

Antigens must be presented by an Antigen-Presenting Cell on their cell surface by an Major Histocompatibility Complex (MHC) molecule

Question 22

what are the B Lymphocytes markers

what MHC do they express

How can they interact with T helper cells

Answer 22

They don’t have any T cell markers

Express CD19 and CD20

Express MHC Class II

Can present antigens to Helper T Cells

Question 23

What are the 3 types of antigen presenting cells

Answer 23

Dendritic Cells

B Lymphocytes

Macrophages (activated)