2 - Cells and Tissues of the Immune System

Question 1

What is the evolutionary purpose of the immune system?

Answer 1

To prevent and eradicate infections that we’ve already come across, but also that we’ve yet to cross paths with and cannot predict.

Question 2

Define infection What types of species are infectious?

Answer 2

Invasion and multiplication of one species in the body of a second species at the expense of the second species.

Viruses, bacteria, fungi, eukaryote parasites.

Question 3

Which cells are phagocytes?

Answer 3

Neutrophils
Monocytes
Macrophages
Dendritic cells

Question 4

Which cells are granulocytes?

Answer 4

Eosinophils
Basophils
Mast cells

Question 5

What white blood cells are lymphocytes?

Answer 5

T helper cells 
Cytotoxic T cells 
Regulatory T cells 
B cells 
Plasma Cells

Question 6

Where do immune cells originate before and after birth? When does this occur?

Answer 6

WBC development begins 23 days post-fertilization in fetal liver where stem cells colonize.

At ~10.5 weeks post-fert, progenitor stem cells colonize the bone marrow.

After birth they only originate from bone marrow.

Question 7

What are generative (primary) lymphoid organs? What is their function?

Answer 7

Bone marrow and thymus.

Where T and B cells mature and become competent to respond to antigens.

Question 8

What are peripheral (secondary) lymphoid organs? What is their function?

Answer 8

Lymph nodes, spleen, mucosal and cutaneous lymphoid tissues.

Where T and B cell responses to antigens are initiated.

Question 9

What is the thymus?

Answer 9

A glandular organ located behind the sternum between the lungs.

T cell progenitors (aka thymocytes) enter the thymus and exit as either helper T cells (aka TH cell or CD4+ T cell) or cytotoxic T cells (TD or CD8+ T cell).

Question 10

What is a naive T cell? What is a memory T cell? How do their levels change as thymus output decreases (ie with age)?

Answer 10

Naive T cells: have never encountered its cognate antigen

Memory T cell: has encountered cognate antigen

Naive cells decrease with age and memory T cells increase with age.

Question 11

What is an immune privileged organ? What are examples?

Answer 11

Organs that contain few, if any, leukocytes.

Brain, eyes, ovaries, testes, uterus, fetus.

Evolutionarily, the fitness cost of inflammation in these organs is too high. An immune response there would be too damaging.

Question 12

Leukocytes travel to tissues via ______ and exit via _____.

Answer 12

travel to tissues via vasculature and exit via lymphatics.

Lymphatics eventually deliver fluid back to vasculature via the thoracic and right lymphatic duct.

Question 13

What directs the movement of lymph?

Answer 13

Mainly contraction of skeletal muscles.

Pulses in arteries.

Question 14

What are lymph nodes? What do they contain?

Answer 14

Encapsulated structures that interrupt the course of lymphatic vessels that are well-suited to detect pathogens from draining tissues.

Contain T and B cells.

Question 15

When do lymph nodes get enlarged?

Answer 15

When the draining tissue is infected.

Question 16

What are antigen presenting cells (APCs)? How do they enter and exit the lymph node?

Answer 16

Leukocytes that engulf antigens in tissues and travel through lymphatics to introduce (present) the antigen to T and B cells.

Enter via afferent lymphatic vessel, exit via efferent lymphatic vessel.

Question 17

How do T and B cells enter and exit the lymph node?

Answer 17

Through high endothelial venules (HEVs) which connect to the vasculature,.

Question 18

What is the organization of T and B cells in lymph nodes in the absence of an infection?

Answer 18

T cells reside in the T cell zone, also called the parafollicular cortex (middle)

B cells reside in the B cell zone, also called the lymphoid follicle (outside).

Question 19

What are germinal centers?

Answer 19

Specialized structures in lymphoid organs that develop during T-dependent B cell responses.

Occurs when T and B cells interact.

Question 20

What is the spleen?

Answer 20

A highly vascularized organ that captures pathogen products present in the blood.

The spleen is to vasculature as the lymph node is to lymphatics.

Question 21

What is the location of the spleen called where leukocytes are concentrated? What is the organization?

Answer 21

White pulp: the structural units of immunity in the spleen.

B cells around the perimeter in B cell zones and T cells in center.

Question 22

What separates the white and red pulp of the spleen?

Answer 22

The marginal zone.

Question 23

How are the T cells of the spleen organized?

Answer 23

They form a pariarteriolar lymphoid sheath (PALS) around a center arteriole.

Question 24

What are MALT, SALT, and BALT? What do these have in common?

Answer 24

Mucosa-associated lymphoid tissue.

Skin-associated lymphoid tissue

Bronchus associated lymphoid tissue

They’re specialized lymphoid tissue that exit in locations with the highest exposure to microorganisms.

Question 25

Where can MALT, SALT, and BALT be found? How are they organized?

Answer 25

Under the epithelia of the GI tract, skin epithelia, and respiratory tract.

Organized in a similar way as lymph nodes.

Question 26

What is the most specific way to classify immune cell types?

Answer 26

Cluster of differentiation (CD) system - which has numerical designations.

Each CD represents a unique cell surface protein.

Question 27

What is the purpose of flow cytometry? How does it work?

Answer 27

Used to measure frequency of each type of cell (ie the basis for the CBC with WBC differential).

Complex mixture of cells is treated with CD-specific fluorophore-conjugated antibodies and run in a flow cytometer so lasers can activate the fluorophore and detectors measure the presence or absence on each cell.

Question 28

What is an adjuvant?

Answer 28

A substance present in the same environment as the antigen, and promotes the generation of an antigen-specific immune response (eg bacterial products).

Question 29

What is the function of humoral (adaptive) immunity?

Answer 29

Block infections and eliminate extracellular microbes via B lymphocytes.

Question 30

What is the function of cell-mediated (adaptive) immunity?

Answer 30

Elimination of phagocytosed microbes via helper T lymphocytes.

Kill infected cells and eliminate reservoirs of infection via cytotoxic T lymphocytes.

Question 31

What is a vaccine?

Answer 31

An antigen/adjuvant mixture used to stimulate production of antibodies and provide immunity against one or several diseases.

Used to act as an antigen without inducing the disease.

Question 32

What do vaccines do to the body?

Answer 32

Initiate a primary antibody response and in some cases, a secondary and tertiary response (boosters) so a person has increased protection.