Cells & Organs of the Immune System

Question 1

(T/F) There are many kinds of vertebrate immune cells; some cells present in high frequency than others.

Answer 1

True!

Question 2

Differentiate primary lymphoid organs from secondary lymphoid organs.

Answer 2

Primary lymphoid organs (bone marrow and thymus) are organs where lymphocytes are produced.

In secondary lymphoid organs, mature lymphocytes encounter ANTIGENs for which they express specific receptors.

Question 3

Antigens are molecules that stimulate the immune system + initiate an immune response. What are EPITOPES found in antigens?

Answer 3

EPITOPES are sites within antigens to which antigen receptors binds.

Question 4

Which one of the statements is true?

1. Generating an antibody which can bind an epitope of a conserved covid protein can make a covid-19 vaccine that protects against all variants.
2. Antibodies are T-cell antigen receptors.
3. Only one epitope can be found in an antigen.

Answer 4

1!

For 2, antibodies are B-cell antigen receptors.

For 3, multiple epitopes can be found in an antigen.

Question 5

(T/F) Stem cells are self-renewal and pluripotent and differentiate into cells in a reversible process.

Answer 5

False!

Though stem cells are self-renewal and pluripotent, they differentiate into cells in a IRREVERSIBLE process.

Question 6

Which one of the statements is true regarding Hematopoiesis?

1. Hematopoiesis is a lowly regulated process.
2. The two characteristics of hematopoietic stem cells (HSCs): self-renewal and the potential to differentiate into all kinds of cells.
3. Hematopoiesis is the process of red and white blood cells developing from a pluripotent HSC.
4. The liver is a primary organ that support hematopoiesis.

Answer 6

3!

1. Hematopoiesis is a HIGHLY regulated process.
2. The two characteristics of hematopoietic stem cells (HSCs): self-renewal and the potential to differentiate into MULTIPLE BLOOD cells.
3. The BONE MARROW is a primary organ that support hematopoiesis.

Question 7

Hematopoietic stem cell transplantation (HSCT) is used for which kinds of patients?

Briefly describe how it works.

Answer 7

1. Individuals with a genetically determined immunodeficiency, such as severe combined immunodeficiency (SCID).
2. Leukemia patients (cancerous immune cells).

Radiation wipes out the whole immune system of the recipient and healthy bone marrow cells from a donor are injected.

Question 8

The red marrow that is found in the bones consists of a _______ (net-like structure) framework of ______ cells.

These stem cell niche cells express _______ and ______-bound proteins that regulate cell survival, proliferation, differentiation, and trafficking.

Answer 8

Reticular; Stromal

Soluble; Membrane

Question 9

Which two major types of progenitors are HSCs differentiated into?

Answer 9

1. Common myeloid progenitor cells
2. Common lymphoid progenitor cells

Question 10

White blood cells are also know as ________.

Which one is the most abundant in blood?

Answer 10

Leukocytes

Neutrophil

Question 11

What are phagocytes?

Briefly describe how they do their function.

Answer 11

Phagocytes ingest and destroy microbes.

Microbe binds to phagocyte receptors, where it gets zipped up by the phagocyte membrane and ingested in a PHAGOSOME. Phagosome gets fused with lysosome (phagolysosomes) with enzymes that kill the microbe.

Question 12

_________ and _________ are specialized for phagocytosis.

Answer 12

Neutrophils; Macrophages

*function is almost identical but occurs at different time during an infection

Question 13

Which one of the statements is true?

1. Neutrophils are monomorphonuclear leukocytes, while monocyte/macrophages are polymorphonuclear leukocytes.
2. Neutrophils die after a few hours, while monocytes have a longer lifetime.
3. Macrophages in blood enter tissue and differentiate into monocytes.

Answer 13

2!

1. NeutroPhils are POLYmorphonuclear leukocytes, while MONOcyte/macrophages are MONOmorphonuclear leukocytes.
2. MONOCYTES in blood enter tissue and differentiate into MACROPHAGES.

*pus contains dead neutrophils

Question 14

Briefly describe the roles + timining of neutrophils and monocyte/ macrophages during inflammation:

Answer 14

Neutrophils: first cell type to respond to most infection. rapidly migrates to sites of inflammation within MINUTES. can ingest and kill microbes using REACTIVE OXYGEN INTERMEDIATES (ROI), NITRIC OXIDE (NO), and LYSOSOMAL proteases.

Monocytes/macrophages: dominant effecters for SEVERAL DAYS after infection. can ingest and kill microbes using REACTIVE OXYGEN INTERMEDIATES (ROI), NITRIC OXIDE (NO), and LYSOSOMAL proteases.

Question 14

Answer the following questions:

1. What are Antigen Presenting Cells (APCs)?
2. Which cells express high expression of MHC class II molecules? These are AKA ..?
3. What are the other two antigen presenting cells?

Answer 14

1. APC cells capture antigen, then mature and migrate into SECONDARY lymphoid organs to present antigen on MHC class II molecules to T cells (activates T cells).
2. Dendritic cells! AKA professional APCs.
3. Macrophages and B cells

Question 15

(T/F) Mast cells, basophils, and eosinophils are all similar to each other and involved in clotting response.

Answer 15

False!

Mast cells, basophils, and eosinophils are all similar to each other and involved in ALLERGIC/ ANTI-PARASITIC response.

MEGAKARYOCYTES form platelets-cell fragments placed into circulation for clotting response.

Question 16

What are colony-stimulation factors (CSF)?

Answer 16

Growth factors; they can stimulate the growth and development of various leukocytic or erythroid colonies from marrow cells.

*mostly produces by stromal cells

Question 17

What are the three main types of cells that develop from common lymphoid progenitors?

Answer 17

1. T cells
2. B cells
3. Natural Killer (NK) cells

Question 18

(T/F) Red blood cells appear less smooth and rough compared to lymphocytes.

Answer 18

False!

Red blood cells have smooth surfaces while lymphocytes express many things on their surfaces.

Question 19

Primary (generative) lymphoid organs and secondary (peripheral) lymphoid organs are connected to each other via?

Answer 19

via the blood and lymphatic circulatory systems

Question 20

Briefly answer the following questions:

1. Where do B lymphocytes develop?
2. What are the two niches of the bone marrow? Differentiate them.
3. How do non- hematopoietic stromal cells contribute to B lymphocytes development?

Answer 20

1. niche of the bone marrow
2. ENDOSTEAL/VASCULAR: the most immature B lymphocytes are found closest to the endosteal niche (near the bone), while the more mature B cells have moved into vascular niche (in the bone).
3. Non-hematopoietic stromal cells provide CONTACT-DEPENDENT SIGNALS and SOLUBLE FACTORS that are required for continuous cycling of the HSCs (helps them differentiate as they are moving from endosteal niche to vascular niche)

Question 21

Briefly answer the following questions:

1. Where do T lymphocytes develop (initially and to mature)?
2. How are the cortex and the medulla of the thymus different?
3. What are thermocytes?

Answer 21

1. T lymphocytes initially develop in the bone marrow, but then migrate to the thymus to achieve full maturity.
2. The cortex contains a dense collection of T lymphocytes while the medulla is more sparsely populated with lymphocytes and other cells.
3. Immature T cells

Question 22

(T/F) The stromal cells of the Thymus form a network surrounding developing thymocytes.

Answer 22

True!

Question 23

What are secondary lymphoid organs? Give examples.

Answer 23

Areas where lymphocytes encounter antigen, become activated, undergo CLONAL EXPANSION, and differentiate into EFFECTOR CELLS.

examples: lymph nodes, spleen, mucosa-associated lymphoid tissue (MALT)

Question 24

(T/F) Post-capillary venules contain a thick layer of endothelial cell wall.

Answer 24

False!

They contain a THIN layer of endothelial cell wall, allowing for cells to easy migrate out of blood vessels into tissues and site of infections.

Question 25

Fill in the blanks:

1. Lymph capillaries are ______ than blood capillaries.
2. Lymph capillaries are _______-ended vessels, lined by overlapping endothelial cells with ___-way valves.
3. The lymphatic system collects _________ from their portals of entry and delivers them to the ___________, where they can stimulate _______ immune responses.

Answer 25

1. Larger
2. Close; one (can go in but cant come out)
3. Microbial antigens; lymph nodes; adaptive

Question 26

Which one of the statements is false?

1. Lymph capillaries allow passage of tissue fluid, large proteins, bacteria, viruses, immune cells, and cell debris.
2. Dendritic cells capture microbial antigens and enter capillary vessels.
3. About two liters of lymph are normally returned to circulation each day,

Answer 26

2!

Dendritic cells capture microbial antigens and enter LYMPHATIC vessels.

Question 27

How are T-cells and B-cells located in the secondary lymphoid organs (lymph nodes/spleen) and what happens during activation events?

Answer 27

Without infection or inflammation, T-cells and B-cells are located separately into DISTINCT microenvironments.

The cells will actively migrate toward each other during activation events for their required interactions.

Question 28

Differentiation of lymphocytes into effector cells takes place in the _______ of secondary lymphoid organs.

T cells meet ____.

B cells further mature into _____ centres with the help of ___ cells.

Both B and T lymphocytes will develop into ____________.

Answer 28

Follicles

APCs

Germinal; T

Long-lived memory cells

Question 29

Which secondary lymphoid organ is the most specialized?

Answer 29

The lymph nodes!

• connected to both blood vessels and lymphatic vessels, lymph nodes are the FIRST organized lymphoid structure to encounter antigens that enter tissues spaces.
• provides ideal microenvironments for encounters between antigen and lymphocytes
• about 500 lymph nodes in the human body

Question 30

What are the three roughly concentric regions of the lymph nodes? Describe and differentiate them.

Answer 30

1. The cortex: outermost layer containing mostly B cells, macrophages, and follicular dendritic cells arranged in follicles.
2. The paracortex: populated larger by T cells and also contains dendritic cells that migrated from tissues into lymph nodes
3. The medulla: innermost layer, and the site where the lymphocytes exit (egress) the lymph node through the outgoing (efferent) lymphatics

Question 31

Antigen travels to the cortex of the lymph node via the ________ lymphatic vessels.

Answer 31

Incoming (afferent)

Question 32

1. What is the spleen? What does it specialize in?
2. Which vessels is it supplied by?
3. How do antigens and lymphocytes are carried into and out of the spleen?

Answer 32

1. The spleen (secondary lymphoid organ) is the FIRST LINE of defense against BLOOD-BORNE pathogens. It specializes in filtering blood and trapping blood-borne antigens (impt 4 systemic infections).
2. Blood vessels only
3. Blood-borne antigens and lymphocytes are carried into the spleen through the SPLENIC ARTERY and out via the SPLENIC VEIN.

Question 33

There are red and white pulps found in the spleen. What is the difference between the two?

Answer 33

Red blood cells are compartmentalized in red pulp.

White blood cells are segregated in white pulp, consisting of marginal zone and PALS (periarteriolar lymphoid sheath) which are populated by T cells. The white pulp also surronds the splenic artery.

Question 34

In the spleen, the blood-borne antigens and lymphocytes enter the spleen through the splenic artery, and interact first with cells at the _______ zone.

In this zone, antigen is trapped and processed by ________ cells, which travel to the ______.

Answer 34

marginal; dendritic; PALS

Question 35

MALT (mucosa-associated lymphoid tissue) is another secondary lymphoid organ. What does it do? How does it work?

Answer 35

It is an important layer of defense against infection at MUCOSAL and EPITHELIAL layers.

It organizes RESPONSES to antigens that enter MUCOSAL tissues (the gastrointestinal and respiratory tracts).

It includes a network of FOLLICLES and lymphoid microenvironments associated with the intestines (gut-associated lymphoid tissue).

Question 36

1. Which cells deliver antigens from the intestinal spaces to lymphoid cells in the gut wall?
2. What are Peyer’s patches?

Answer 36

1. M cells in the lining of the gut
2. Nodules of lymphoid follicles found in the small intestine (found in MALT).

*MALT has a lymph node

Question 37

Naive lymphocytes are _______ than effector lymphocytes.

Why?

What about memory lymphocytes?

Answer 37

Smaller; effector cells have more antibodies and toxic granules.

Memory lymphocytes are smaller than effector cells.

Question 38

Which myeloid cell types have granules with enzymes and toxins?

Answer 38

Neutrophils, eosinophils, basophils, and mast cells.