Theme 2a Lymphoid Organs

Question 1

How are lymphoid organs connected to each other and where are they found?

Answer 1

• They are connect by blood and lymphatic vessels.
• They are found throughout the body (bone is everywhere)

Question 2

What are the two types of lymphoid organs?

Answer 2

• Primary (central) => Where lymphocytes are generated and mature.
• Secondary (peripheral) => lymphocytes encounter antigens, become activated, undergo clonal expansion and differentiate into effector cells.

Question 3

What are the primary lymph organs

Answer 3

• Bone marrow: development of B and T cells (site of IgH and IgL rearrangements)
• Thymus: maturation of T cells

Question 4

Thymus
Location?
Structure?

Answer 4

• directly above the heart, under the thyroid
• lobes divided by connective tissue to form lobules. It is divided into the cortex and the medulla.

Question 5

In the thymus, what is in the center: the medulla or the cortex?

Answer 5

The medulla

Question 6

What is the TCR made of?

Answer 6

a beta chain and an alpha chain.

Question 7

during positive and negative selection in the thymus, what percentage of T cells die?

Answer 7

90-95% die.

Question 8

What does MHC stand for and what is it used for?

Answer 8

Major Histocompatibility Complex
It is used to hold an antigen so that a T-cell can detect it.

Question 9

Where does positive and negative selection occur in the thymus?

Answer 9

positive -cortex
negative - medulla

Question 10

What are the secondary lymphoid organs?

Answer 10

• Lymph nodes
• Spleen
• Mucosa- Associated Lymphoid Tissue (MALT)
• Others also exist.

Question 11

What is lymph?
How is lymph moved?
How does it serve the immune system?

Answer 11

• It is a protein rich fluid produced by the leakage of tissues into intercellular areas. It is eventually returned to the blood.
• It moves via muscular movement, and valves prevent back-flow.
• Lymph will pick up antigens and activated lymphocytes and bring them to the secondary lymphoid organs so that an immune response can be induced. Lymph also moves reinforcement activated lymphocytes back to the site of the injury or threat.

Question 12

In the lymph nodes, where is B-cell activity and where is T-cell activity?

Answer 12

B-cells are in the cortex, especially the follicle (outer)
T- cells are in the paracortex (inner)

Question 13

Lymph Nodes
Where do B cells process antigens?
Where do B cells present antigen through a MHC to Th cells?
What does the Th cell do to the B cell upon recognition of antigen?
Where are B- cell germinal centers established?

Answer 13

• B cell follicle zone
• paracortex
• T helper cells activate B-cells and signal for differentiation and clonal expansion.
• B cell follicle zone.

Question 14

Spleen
Function?
Structures?

Answer 14

It protects the body against blood borne pathogens.

• Follicular B-cell zone
• Marginal zone - macrophages and specialized B- cells.
• PALS T-cell zone

Question 15

Where is Mucos-associated lymphoid tissue located?

Answer 15

• digestive (GALT), respiratory and urogenital tracts.

Question 16

What is a type of MALT found in the small intestine?
What are its structures?

Answer 16

• Peyer’s patches
• germinal center filled with proliferative B-cells thicken the intestinal wall.
• dome region projects form the follicle towards the intestinal lumen and is a site of antigen entry.
• interfollicular area contains T cells and allows lymphocyte recirculation.