Cells and Structure of Immune System

Question 1

Why are hematopoietic stem cells important?

Answer 1

We need a constant supply of immune cells, and HSCs allow for that. They are multi-potent, self-renewing sources of WBCs, RBCs, and platelets.

Question 2

What do HSC niches consist of, and what attracts HSCs to them?

Answer 2

• Consist of osteoblasts, sinusoidal endothelial cells, and stromal cells that confer self-renewal potential of HSCs
• Chemical signal gradients attract them to their niches

Question 3

When/why are HSCs “mobilized” to differentiate into immune cells?

Answer 3

• to replenish peripheral WBCs, RBCs, or platelets

- during periods of stress (ex: infection)

Question 4

Why is hematopoiesis important to homeostasis?

Answer 4

It is important because it ensures that the body has enough immune cells circulating to fight infection when it arises. When we are sick, our output of immune cells is faster and larger than normal.

Question 5

Differentiation of an HSC into common myeloid and lymphoid progenitors depends on which stimulating factors and cytokines?

Answer 5

• common myeloid: IL-3, SCF, GM-CSF

- common lymphoid: IL-7

Question 6

Are neutrophils found in healthy tissue?

Answer 6

no, but they will migrate there if an infection is present; otherwise, they are normally found circulating in the blood

Question 7

Which are the most numerous and important cells in innate immune responses?

Answer 7

neutrophils

Question 8

Which immune cells are the phagocytes?

Answer 8

• neutrophils
• macrophages
• monocytes
• dendritic cells
• eosinophils can be, but it’s not a major function

Question 9

Describe what neutrophil extravasation is.

Answer 9

It is the organized manner in which neutrophils cross the blood vessel wall to enter inflamed tissue. Neutrophils are the first wave of cells to do this.

Question 10

Monocytes are circulating precursors to __________.

Answer 10

macrophages AND dendritic cells

Question 11

What is the purpose of tissue macrophages producing potent cytokines (TNF alpha, IL-6, IL-1 beta) upon activation?

Answer 11

cytokines recruit more cells to the site of invasion

Question 12

Are dendritic cells phagocytic? If so, do they result in formation of a phagolysosome?

Answer 12

They ARE phagocytic, but they do NOT result in formation of a phagolysosome

Question 13

Which immune cells are the antigen presenting cells?

Answer 13

• macrophages
• dendritic cells
• B-cells

Question 14

True or false: once neutrophils enter infected tissue and perform their duty, they are returned to the circulation.

Answer 14

False- neutrophils are short-lived and die soon after accomplishing one round of phagocytosis.

Question 15

What is the major role of dendritic cells?

Answer 15

To act as antigen presenting cells and activate T lymphocytes. They are the main messenger between the innate and adaptive immune system. They are also phagocytic, although this is not their major role.

Question 16

What is the main function of eosinophils, and where are they mostly found?

Answer 16

They have a primary role in defense against parasites, and they are found mostly in subepithelial tissues.

Question 17

What are two kinds of effector functions that eosinophils express when activated?

Answer 17

1) Release highly toxic granule proteins and free radicals

2) Synthesize chemical mediators, including prostaglandins, leukotrienes, and cytokines

Question 18

Is the effect of eosinophils in an allergic reaction protective or damaging?

Answer 18

damaging (continued presence=characteristic of chronic allergic damage)

Question 19

How do eosinophils, basophils, and mast cells interact?

Answer 19

Eosinophil degranulation results in release of major basic protein, which causes the degranulation of mast cells and basophils.

Question 20

What is the role of basophils?

Answer 20

They are less important in the immune system but have a similar role to eosinophils (parasite defense and allergic rxns) and also release histamine and IL-4 and IL-13 from their granules.

Question 21

Where are mast cells found?

Answer 21

peripheral tissues, especially the skin, intestines, and airway mucosa

Question 22

Why are the inflammatory mediators released by mast cells so rapidly acting?

Answer 22

the inflammatory mediators (including histamine and various proteases) are pre-formed

Question 23

Are natural killer cells lymphoid or myeloid? Are they part of the innate or adaptive immune response?

Answer 23

they are lymphoid, but they lack the antigen-specific receptors of adaptive immune cells

Question 24

What is the important function of NK cells?

Answer 24

They play a role in the early innate response to viral infections, before the adaptive immune response has developed.

Question 25

The immediate reaction caused by mast cell degranulation is followed by what?

Answer 25

a more sustained inflammation due to the recruitment of other effector leukocytes, including T-helper lymphocytes, eosinophils, and basophils

Question 26

Immunological memory is only possible via what?

Answer 26

highly variable antigen receptors on the surface of lymphocytes, by which they recognize and bind antigens

Question 27

What causes differentiation of a B-cell into a plasma cell?

Answer 27

binding of a B-cell’s specific antigen to its receptor

Question 28

True or false: plasma cells secrete antibodies that have the SAME antigen specificity as the B-cell receptor that started the differentiation.

Answer 28

true

Question 29

What causes proliferation and differentiation of a T-cell into one of several functional effector T-cells?

Answer 29

when a T-cell’s specific antigen (usually presented by an antigen-presenting cell) binds to its receptor

Question 30

What are the 3 broad classes of activity of effector T-cells?

Answer 30

• Cytotoxic T-cells: kill other cells infected with viruses or other intracellular pathogens
• Helper T-cells: provide signals, often in the form of cytokines that activate the functions of other cells, including B-cell production of Ab and macrophage killing of engulfed pathogens
• Regulatory T-cells: suppress the activity of other lymphocytes and help limit the damage of immune responses

Question 31

How are memory cells formed?

Answer 31

They are formed by the differentiation of certain B and T-cells that are activated by an antigen. Memory cells are responsible for the long-lasting immunity that can follow exposure to disease or vaccination.

Question 32

The major exchange of information between the innate and adaptive immune system occurs where?

Answer 32

in lymphoid tissue, where innate cells traveling in the lymph encounter adaptive cells traveling in the blood vessels to exchange information about a pathogen

Question 33

How do innate vs. adaptive cells sense pathogens?

Answer 33

• innate cells sense pathogens based on broad characteristics, like cell surface sugars or other molecular patterns shared by pathogens
• adaptive cells are specific for each individual pathogen

Question 34

What is the relationship of the spleen to the lymphatic system?

Answer 34

It has no direct connection with the lymphatic system; however, it collects antigens from the blood and is involved in immune responses to blood-borne pathogens.

Question 35

Where do antigens and lymphocytes eventually encounter each other?

Answer 35

in the peripheral lymphoid organs (lymph nodes, spleen, mucosal lymphoid tissues)

Question 36

Lymph nodes are ___________ lymphoid organs located at the __________ of the lymphatic system.

Answer 36

highly organized; points of convergence of vessels

Question 37

What is the path of a naive lymphocyte vs. an activated lymphocyte?

Answer 37

A naive lymphocyte will travel through a lymph node and then recirculate, whereas an activated lymphocyte will stay in the lymph node and undergo a period of proliferation and differentiation. Once differentiated, lymphocytes leave the lymph node as effector cells via the efferent lymphatic vessels, which return them to the blood stream, which carries them to the tissues where they will act (this process takes 4-6 days from the time the antigen is recognized).

Question 38

Where do B-cells vs. T-cells localize in the lymph node?

Answer 38

T-cells localize in the paracortical areas first, while B-cells localize in the primary lymphoid follicles first.

Question 39

How do naive lymphocytes enter the lymph node from the blood stream?

Answer 39

via specialized postcapillary venules (HEVs - High Endothelial Venules)

Question 40

What is the difference between the red pulp and white pulp of the spleen?

Answer 40

red pulp (majority of spleen) is the site of RBC disposal and iron recycling; white pulp is the site of immune cells and responses

Question 41

Most pathogens enter the body through _________.

Answer 41

mucosal surfaces

Question 42

True or false: the mucosal immune system is estimated to contain far more lymphocytes than the entire rest of the body.

Answer 42

False- it contains as many lymphocytes as the rest of the body

Question 43

What are examples of GALT (gut-associated mucosal tissue)?

Answer 43

tonsils, adenoids, appendix, Peyer’s patches (in sm. intestine)

Question 44

What do GALTs do?

Answer 44

collect antigens from the epithelial surface of the GI tract; lymphocytes form a follicle with a large central dome of B-cells surrounded by a smaller number of T-cells; dendritic cells within Peyer’s patches present antigen to T-cells
(GALT is made up of several types of lymphoid tissues that store immune cells that can carry out attacks and defend against pathogens)