Immunology 2- Immune cells and organs

Question 1

What are the primary lymphoid organs

Answer 1

The major sites of lymphopoiesis, which is the generation of lymphocytes. Lymphoid stem cells differentiate into mature functional mature lymphocytes- located in the thymus and bone marrow.. B lymphocytes and T lymphocytes are produced.

Question 2

What are the secondary lymphoid organs

Answer 2

lymphoid organs are where lymphocytes can interact with antigen and with other lymphocytes

spleen
lymph nodes
mucosal associated lymphoid tissues (MALT

Question 3

Describe the basic structure of the thymus

Answer 3

A bi-lobed organ located in the thorax- found in mammals. Each lobe is organised into lobules and in each lobule are the histologically defined regions of the cortex and the medulla. The cortex contains the immature thymocytes, some of which are selected to become thymocytes in the medulla.

Question 4

What is seen in the thymus during infections

Answer 4

There are no obvious changes to the thymus during infections.

Question 5

Where may mucosal associated infections occur

Answer 5

The nose and the gut.

Question 6

Describe the structure of the thymus

Answer 6

Learn from diagram!

Question 7

What does the purple region of the thymus indicate

Answer 7

Proliferating lymphocytes.

Question 8

How does thymic output change with age

Answer 8

Thymic output decreases with age due to atrophies of thymus, Although the total T cells present is the same, the number of new T cells decreases, hence older people have less new specificities to new pathogens.

Question 9

What happens to the bone marrow during infections

Answer 9

Increased White cell production.

Question 10

How do the locations of the bone marrow change from foetus to adult

Answer 10

In the foetus, the bone marrow is present in all bones, as well as in the liver and spleen. The bone marrow is very cellular.
In Adults, the bone marrow is present in mostly flat bones. Vertebrae Iliac bones Ribs, ends of long limb bones. The marrow contains fat.

Question 11

What is found in Hassall’s corpuscle of the thymus

Answer 11

Fibroblasts, which are important in the production of an important type of T lymphocyte.

Question 12

What is the difference between red marrow and yellow marrow

Answer 12

Red-produces blood cells

Yellow-contains fat.

Question 13

What is the lymphatic system

Answer 13

Fluid drained from
between tissue cells
absorbed into lymph

2 to 3 litres of lymph
are returned to the
blood each day (via
superior vena cava)

Question 14

Describe the structure of the lymph node

Answer 14

See Diagram!

Question 15

Where are T cells found in the lymph node

Answer 15

The parafollicular cortex

Question 16

Where are B cells found in the lymph node

Answer 16

The lymphoid follicle.

Question 17

Why is the physical organisation of the lymph nodes important

Answer 17

Lots of nodes found all over the body, this means that it is more likely that the receptor will encounter the antigen to trigger an immune response.

Question 18

What happens in the germinal centres of the lymph nodes

Answer 18

Site of proliferation of B cells, enlarged during infection, which is a sign of immune response.

Question 19

What happens during passage of the lymph

Answer 19

During passage of lymph through the node, there is removal of particulate antigens by the phagocytic cells and then this is transported to the lymphoid regions of the node. The cortex is a B cell area. The paracortex is a T cell area.

Question 20

What is the basic role of the spleen

Answer 20

Filter for antigens in the blood.

Question 21

What are the two different types of tissue present in the spleen

Answer 21

Red Pulp and White Pulp.

Question 22

What is the difference in function between white pulp and red pulp

Answer 22

Red pulp-filter for blood.

White pulp- lymphoid tissue which constitutes the major initiator of responses to blood-borne antigens.

Question 23

Describe the structure of the spleen

Answer 23

See diagrams!

Question 24

Where is the B cell zone of the spleen

Answer 24

The primary follicle.

Question 25

Where is the T cell zone of the spleen

Answer 25

Periarterial lymphatic sheath (PALS)

Question 26

What tissue is involved in the first line of defence

Answer 26

The epithelial tissue forms the first line of defence; The mucosae and skin form a physical barrier to pathogens. They have a very large surface area, and is mostly a single layer of cells.

Question 27

How are these epithelial tissues heavily defended by the immune system.

Answer 27

Mucosa Associated Lymphoid Tissue (MALT) | Cutaneous immune system.

Question 28

Describe the Gut Associated Lymphoid Tissue

Answer 28

Intraepithelial lymphocytes- from lymph nodes. | Peyer's patch

Question 29

What is Peyer's patch.

Answer 29

Large aggregation of lymphocytes and follicles, predominately B lymphocytes, contain germinal centres during immune responses. On top- specialised areas of the mucosal epithelium called microbial cells (M cells), sample antigens in the gut lumen, passed into lymphocytes in Peyer's patch, mostly commensal, partially stimulate immune system, this is essential in its development,

Question 30

Describe the two types of immune cells found in the cutaneous immune system.

Answer 30

Intraepidermal lymphocytes, epidermal Langerhans cells. Dermal dendritic cells- present antigens from skin in lymph nodes.

Question 31

How does the body ensure that the antigen meets a lymphocyte with the specific receptor

Answer 31

Anatomical structure of the immune system | -Lymphocyte recirculation

Question 32

Describe the circulation of lymphocytes

Answer 32

Naïve lymphocytes circulate constantly from the blood into the secondary lymphoid tissue, and leave the vasculature through a specialised section of the post capillary venule known as the high endothelial venule (HEV). They move from the lymph node to the lymphoid vessels and eventually return to the blood via the lymphatic duct. In the presence of an infection, those cells which recognise an infectious agent are held in the lymphoid tissue where they proliferate and differentiate. Those that aren't activated may die in the lymphoid tissue.

Question 33

Describe the extravasation of naïve lymphocytes into the lymph nodes through the HEV

Answer 33

Initially, naïve lymphocytes roll on the surface of the HEV via low affinity interactions between selectin on the lymphocytes and the CD34 receptor on the HEV. T cell then changes conformation of integrin to a high affinity binding form where it binds to ICAM on the HEV. When integrins bind to ICAM, rolling stops, lymphocyte arrested, migrates through HEV. Chemokines on HEV binding to receptors on naive lymphocytes triggers the conformational change in adaptin.

Question 34

What is ICAM

Answer 34

Intracellular Adhesion Molecule.

Question 35

What are lymphocytes

Answer 35

Small cells with agranular cytoplasm and a large nucleus

Question 36

Can B and T lymphocytes be distinguished under a microscope using conventional stains

Answer 36

No

Question 37

What is the cluster of differentiation

Answer 37

Internationally recognised system of identifying cell surface molecules present on leukocytes, as well as other cell types. Originates from the fact that these molecules were first identified using monoclonal antibodies made in different labs around the world. Each set of antibodies that recognise a particular molecule forms a cluster. Since 1982, International workshops have been held regularly to assign CD numbers to particular cell surface molecules.

Question 38

What is the CD system most commonly used for

Answer 38

Used as cell markers- more than 350 CD numbers assigned. Not just cell markers, but also important functional molecules (involved in the way I which the lymphocytes recognise the antigen). They are also present on other types of cells to haematopoietic cells, such as certain adhesion molecules.

Question 39

How many T lymphocytes do we have

Answer 39

``` T cells 1.5 x 103 per l 1.5 x 109 per litre 5 litres of blood 7.5 x 109 in the blood Blood contains 2% of the total pool 50 x 7.5 x 109 = 3.75 x 1011 ```

Question 40

Outline the receptors expressed on T lymphocytes

Answer 40

All T cells express CD3. Gamma-delta TCR-10% in blood. Alpha-beta TCR-90% in blood. Alpha-beta CD3 T cells can also express either CD4 (2/3) or CD8 (1/3).

Question 41

What is the role of CD4+ T cells

Answer 41

T helper cells, T regulatory cells- secrete cytokines.

Question 42

What is the role of CD8+ cells

Answer 42

Cytotoxic T cells. Lyse infected cells and secrete cytokines.

Question 43

Describe T cell antigen recognition

Answer 43

T cells only recognise processed antigen presented at the surface of another cell using T cell receptor The antigen is presented by an MHC molecule (Major Histocompatibility Complex)

Question 44

Describe the B lymphocytes

Answer 44

Produced by and develop in bone marrow - Surface antigen receptor : immunoglobulin like molecule - Express CD markers CD19 & CD20 (not CD3, CD4 or CD8) - Express MHC Class II (can present antigen to helper T cells) - Effector function is to produce antibodies

Question 45

Describe B cell antigen recognition

Answer 45

B cells recognise intact antigen free in body fluids (so not presented by another molecule) or on cell surfaces Use B cell receptor, a membrane anchored form of antibody linked to signalling subunits

Question 46

What are the two fates of lymphocytes stimulated by an antigen

Answer 46

Effector lymphocytes | Memory lymphocytes

Question 47

What are APCs

Answer 47

``` APC’s are cells that can present processed antigen (peptides) to T lymphocytes to initiate an adaptive (acquired) immune response These cells include: Dendritic cells (DC) B lymphocytes Macrophages (activated) ```

Question 48

What is meant by extravasation

Answer 48

Process of lymphocytes entering lymph nodes.

Question 49

What do all lymphoid tissues have

Answer 49

HEV (except the spleen) and distinct areas for B cells and T cells.

Question 50

How do chemokines cause cells to move in a particular direction

Answer 50

Follow chemokines down a gradient- chemotaxis.

Question 51

What is a role of lymphoid tissue

Answer 51

Filters fluid to give lymphocytes a chance of finding the complementary antigen.

Question 52

Where is MALT found

Answer 52

In the linings of the respiratory, gastrointestinal and reproductive tracts.

Question 53

What is meant by immunologically privileged sites

Answer 53

Sites where no lymphoid cells are present (eyes, testes and brain).

Question 54

What is the ultimate purpose of trafficking or recirculation

Answer 54

To connect the various lymphoid compartments to create one system.