Organisation of immune system

Question 1

What are the primary lymphoid organs and their functions?

Answer 1

Thymus and bone marrow

Where lymphocytes are produced by lymphopoiesis

Question 2

What are the secondary lymphoid organs and their functions?

Answer 2

Spleen, Lymph nodes and mucosal associated tissues (MALT)

Where lymphocytes interact with antigens and each other

Question 3

What is the structure of the thymus?

Answer 3

Two lobes → lobules containing Hassall’s corpuscles → fibroblast cells involved in the formation of regulatory T cells

Question 4

What is a lymphoid organ?

Answer 4

An organ where lymphocytes develop and congregate

Question 5

How does the thymus change with age?

Answer 5

Decrease in size
Reduced output
Less diverse T cells produced BUT total number produced same

Question 6

Where is the thymus located?

Answer 6

Anterior-superior mediastinum
Behind sternum
Anterior to heart

Question 7

Where does hematopoiesis occur in adults?

Answer 7

Bone marrow of Long/flat bones

e.g. Long bones of limbs, vertebrae, ribs

Question 8

Where does hematopoiesis occur in the fetus?

Answer 8

All bones
Liver
Spleen

Question 9

What are the two types of bone marrow?

Answer 9

Red - hematopoietic tissue

Yellow - Fatty tissue

Question 10

How does hematopoiesis change during infection?

Answer 10

Increased white cell production

Question 11

What are the functions of the lymphatic system?

Answer 11

Provides drainage to prevent build up of ECF

Involved in WBC interaction

Question 12

What is the function of lymph nodes?

Answer 12

Filters the antigens in lymph

Question 13

What is the general structure of a lymph node?

Answer 13

Lymphoid cells on outer edge containing B cells
(If ongoing immune response then B cells will proliferate and produce antibodies in the Germinal centres)
T cells closer to sinus than B cells, macrophages present to engulf pathogens

Question 14

What changes in lymph nodes occur during infection?

Answer 14

Enlargement - due to proliferation of immune responses

Question 15

What is the structure of the spleen?

Answer 15

White pulp surrounding blood vessels - contains lymphocytes
PALS - periarterial lymphatic sheath - surrounds arteries within white pulp, contains T cells
Primary follicles - adjacent to PALS - contain B cells
Red pulp - site of RBC turnover

Question 16

What is the function of the spleen?

Answer 16

Filters antigens in the blood

Question 17

What is the role of epithelia in the immune response?

Answer 17

1st line of defence - PHYSICAL barrier formed by mucosa and skin

Question 18

What are the defence mechanisms associated with epithelia and why are they needed?

Answer 18

Lymphoid tissues associated with sites of likely infection
MALT/GALT/SALT
Needed because large surface area and may be single celled ∴ vulnerable

Question 19

Describe the organisation of gut associated lymphoid tissue (GALT)

Answer 19

Special mucosal epithelium over Peyer’s patches (large aggregates of lymphocytes that drain to lymph nodes)
-Contains microfold cells to sample antigens in gut to present to lymphocytes for surveillance

Question 20

Why are lymphocytes recirculated?

Answer 20

Lymphocytes with the correct specificity and antigen may not meet due to large number of T and B cells with different specificities
∴Cells travel through blood and lymphoid tissues until they meet antigen/die

Question 21

What are the steps of lymphocyte recirculation?

Answer 21

1) Lymphocyte produced in 1° lymphoid organ
2) Lymphocyte travels to blood
3) Lymphocyte travels to tissue
4) Lymphocyte travels to 2° lymphoid organ
5) Back to blood (step 2)

Question 22

What are high endothelial venules (HEV)?

Answer 22

Specialised vessels that allow entry of lymphocytes into the lymphatics

Question 23

What is the process of HEV extravasation?

Answer 23

1) Rolling of naive T-cell along endothelium to HEV
2) Selectin (Tcell) binds weakly to endothelial CD34(HEV)
3) Chemokines on HEV bind to T-cell receptors ∴ integrins have higher affinity
4) Integrins bind and T cell enters tissue by transendothelial migration

Question 24

What are the two major classes of lymphocytes?

Answer 24

B cells

T cells

Question 25

How can you distinguish between lymphocyte classes?

Answer 25

System is used to discriminate hematopoietic cells based on their cell surface proteins All B cells have MHC II, CD19 and CD20 (not 3,4,8) All T cells have CD3 (some 4,8)

Question 26

What form of antigens do B cells recognise?

Answer 26

Recognises intact antigens in body fluids or on cell surfaces using B cell receptors - membrane anchored form of antibody

Question 27

What form of antigens do T cells recognise?

Answer 27

Processed antigens presented at surface of another cell using a TCR by a Major Histocompatability Complex (MHC)

Question 28

List the cell types of the immune system

Answer 28

``` Neutrophils Eosinophils Basophils Monocytes/Macrophages Mast cells Dendritic cells NK cells B cells T cells ```

Question 29

What are the functions and distinguishing features of neutrophils?

Answer 29

Multi-lobed nucleus First cells to site of tissue damage Phagocytosis

Question 30

What are the functions and distinguishing features of eosinophils?

Answer 30

``` Phagocytosis Release granules Defend against parasitic infection Help with B cell responses producing IgA Stain with eosin ```

Question 31

What are the functions and distinguishing features of basophils?

Answer 31

Release granules May act as antigen presenting for type 2 immunity Antibody mediated

Question 32

What are the functions of monocytes/macrophages?

Answer 32

Important for phagocytosis Release cytokines as mediators Are antigen presenting for T cells

Question 33

What are the functions of mast cells?

Answer 33

Release granules containing histamine

Question 34

What are the functions of dendritic cells?

Answer 34

Capture and present antigens to T cells

Question 35

What are the functions of NK cells?

Answer 35

Lyse infected cells