Organs of the Immune System

Question 1

Where are lymphoid cells first produced?

Answer 1

in fetal omentum, liver and yolk sac

Question 2

Where are lymphoid cells produced in adults and older fetuses?

Answer 2

bone marrow

Question 3

What is bone marrow?

Answer 3

a hematopoietic organs that gives rise to all blood cells

Question 4

Whata re the primary lymphoid organs?

Answer 4

bone marrow, thymus, Bursa of Fabricius in birds

Question 5

What are the secondary lymphoid organs?

Answer 5

spleen, lymph nodes, unencapsulated lymphoid tissue, Peyer’s patches

Question 6

Where do T lymphocytes mature?

Answer 6

thymus

Question 7

Where do B lymphocytes develop and mature?

Answer 7

• Bursa of Fabricius (birds only)
• Bone marrow (primates and rodents)
• Intestinal lymphoid tissue (rabbits, ruminents, pigs)

Question 8

True or false? primary lymphoid organs are usually sites of lymphocyte interaction with microbial antigens.

Answer 8

False - not unless there is an infection in the organs

Question 9

What is meant when the thymus is said to undergo involution?

Answer 9

thymus is large in newborns but small to invisible in adults. Thymus has shrunken

Question 10

What are the functions of the thymus?

Answer 10

• maturation of lymphocytes

- lymphocytes learn to differentiate foreign antigen from self antigen here

Question 11

What happens to thymocytes with receptors that bind strongly to self-antigens?

Answer 11

destroyed through process calle apoptosis - negative selection

Question 12

What happens if a thymocyte cannot bind any MHC II molecules?

Answer 12

they are also removed

Question 13

What thymocytes are allowed to live?

Answer 13

the ones that recognize MHC II/Ag complexes with moderate affinity
- positive selection

Question 14

What do the positively selected thymocytes do when they mature and leave to thymus as mature lymphocytes?

Answer 14

populate the secondary lymphoid organs

Question 15

What regulates the maturation process of thymocytes?

Answer 15

a mixture of cytokines and thymic hormones such as thymosins, thymopoietins, thymulin, and thymostimulins

Question 16

What is the Bursa of Fabricius similar to?

Answer 16

the thymus

Question 17

What is the function of the Bursa of Fabricius?

Answer 17

antibody-forming cells mature and differentiate - negative and positive selection of B lymphocytes

Question 18

What are secondary lymphoid organs divided into?

Answer 18

• encapsulated organs (lymph nodes, spleen)

- Non-encapsulated tissues (mucosal lymphoid aggregates)

Question 19

When do secondary lymphoid organs develop?

Answer 19

develop in late fetal life and persist in adults

Question 20

True or Fasle? Secondary lymphoid organs enlarge in response to antigenic stimulation.

Answer 20

True

Question 21

What do secondary lymphoid organs contain? What do they do?

Answer 21

contain dendritic cells which trap and process antigens and later present these antigens to lymphocytes to initiate an immune response

Question 22

What are lymph nodes?

Answer 22

• round/bean-shaped encapsulated organs that act as filters of lymph to trap antigens

Question 23

What are the regions of the lymph nodes?

Answer 23

cortex (outer), medulla (inner) and paracortex (between the two)

Question 24

Where are B lymphocytes found in lymph nodes?

Answer 24

in the cortex in what are called germinal centers surrounded by capsules

Question 25

Where are T cells and Dendritic cells found in lymph nodes?

Answer 25

paracortex

Question 26

What is the principle function of a lymph node?

Answer 26

to facilitate the interaction between antigen presenting cells (APCs) and antigen sensitive T and B lymphocytes

Question 27

What is the spleen?

Answer 27

a large encapsulated organ found in almost all vertebrates | - structured by a network of connective tissue trabeculae

Question 28

What two forms of tissue does the spleen consist of?

Answer 28

red pulp - blood filtering and RBC storage | white pulp - Where immune response occurs - rich in lymphocytes

Question 29

What does the spleen do?

Answer 29

- filters blood for blood-borne antigens, cellular debris, and aged blood cells - stores RBCs, platelets, recycles iron

Question 30

What are peyer's patches?

Answer 30

non-encapsulated lymphoid tissue located in the wall of the small intestines (in ruminents, pigs, horses, dogs, and humans they are found in the ileum)

Question 31

What do peyer's patches contain?

Answer 31

densly packed lymphoid follicles containing only B lymphocytes

Question 32

What are Mucosal-Associated Lymphoid Tissue (MALT)?

Answer 32

non-encapsulated lymphoid aggregates scattered throughout the surfaces of the body and make up a large portion of the total lymphoid tissue

Question 33

What are some Mucosal-Associated Lymphoid Tissues (MALT)?

Answer 33

- Gastrointestinal-associated lymphoid tissue (GALT) - Bronchial-associated lymphoid tissue (BALT) - Nasal-associated lymphoid tissue (NALT) - Conjunctiva-associated lymphoid tissue (CALT)

Question 34

What are Innate lymphoid cells (ILCs)?

Answer 34

immune cells that belong to the lymphoid lineage but do not express antigen-specific receptors - secrete high concentrations of cytokines that are implicated in innate immunity, inflammation, lymphoid tissue formation, and tissue remodeling

Question 35

What are the groups of Innate lymphoid cells?

Answer 35

- Group-1 ILCs - Group-2 ILCs - Group-3 ILCs

Question 36

What transcription factors do Group-1 ILCs depend on? What do they produce?

Answer 36

are under the control of the T-bet transcription factor and include NK cells and ILC1 cells. Secrete sytokines such as IFN-gamma, and TNF-alpha in response to intracellular pathogens

Question 37

What transcription factors do Group-2 ILCs depend on? What do they produce?

Answer 37

rely on GATA-3 nd ROR-alpha transcription factors. Produce IL-5, IL-9 and IL-13 in response to extracellular parasite infections

Question 38

What transcription factors do Group-3 ILCs depend on? What do they produce?

Answer 38

include lymphoid tissue inducer cells (LTi) and ILC3 cells, are under the control of the ROR-gammat transcription factor. produce IL-17 and IL-22. required for the development of lymphoid tissues