Chapter 8: The Immune System

Question 1

Innate immune system

Answer 1

Composed of defenses that are always active against infection, but lack the ability to target specific invaders over others; AKA nonspecific immunity

Question 2

Adaptive or specific immunity

Answer 2

Defences that target a specific pathogen; slower to act but can maintain immunological memory of an infection to be able to mount a faster attack in subsequent infections

Question 3

Bone marrow

Answer 3

Produces all of the leukocytes (white blood cells) that participate in the immune system through the process of hematopoiesis

Question 4

Spleen

Answer 4

Site of blood storage and activation of B-cells which turn into plasma cells to produce antibodies as part of adaptive immunity; when B-cells leave the bone marrow, they are considered mature but naive; humoral immunity

Question 5

Thymus

Answer 5

Site of T-cell maturation; a small gland in front of the pericardium (sac that protects the heart); agents of cell-mediated immunity

Question 6

Lymph nodes

Answer 6

A major component of the lymphatic system, provide a place for immune cells to communicate and mount an attack; B-cells can be activated here as well

Question 7

GALT

Answer 7

Gut-associated lymphoid tissue; include tonsils and adenoids in the head

Question 8

Peyer’s patches

Answer 8

In the small intestine

Question 9

Appendix

Answer 9

Has lymphoid aggregates

Question 10

Lymphocytes

Answer 10

Responsible for antibody production, immune system modulation, and targeted killing of infected cells

Question 11

First line of defence

Answer 11

Skin (integument); physical barrier between the outside world and our internal organs, excluding most bacteria, viruses, fungi, and parasites from entering the body

Question 12

Defensins

Answer 12

Antibacterial enzymes can be found on the skin

Question 13

Complement

Answer 13

Consists of a number of proteins in the blood that act as a nonspecific defence against bacteria; punch holes in the cell walls of bacteria, making them osmotically unstable

Question 14

Classical pathway

Answer 14

Requires the binding of an antibody to a pathogen

Question 15

Alternative pathway

Answer 15

Does not require antibodies

Question 16

Interferons

Answer 16

Proteins that prevent viral replication and dispersion; cause nearby cells to decrease production of both viral and cellular proteins; also decrease the permeability of these cells, making it harder for a virus to infect them; upregulate MHC class I and II molecules, resulting in increased antigen presentation and better detection of the infected cells by the immune system; responsible for “flu-like” symptoms

Question 17

Macrophages

Answer 17

1) Phagocytize the pathogen
2) Digest the pathogen with enzymes
3) Present little pieces of the invader (mostly peptides) to other cells using a protein called the major histocompatibility complex (MHC) - binds to a pathogenic peptide (also called an antigen) and carries it to the cell surface; also release cytokines - chemical substances that stimulate inflammation and recruit additional immune cells to the area

Question 18

MHC class I molecules

Answer 18

All nucleated cells in the body display MHC class I molecules; any protein produced within a cell can be loaded onto MHC-1 and presented on the surface of the cell; AKA endogenous pathway; allows for monitoring cell health; cells that have been invaded by intracellular pathogens can then be killed by a certain group of T-cells to prevent infection of other cells

Question 19

MHC class II molecules

Answer 19

Mainly displayed by professional antigen-presenting cells like macrophages, dendritic cells in the skin, some B-cells and certain activated epithelial cells; AKA exogenous pathway; may result in activation of both the innate and adaptive immune systems

Question 20

Pattern recognition receptors

Answer 20

Special receptors on macrophages and dendritic cells; best described are toll-like receptors; able to recognize the category of the invader and allows for the production of appropriate cytokines to recruit the right type of immune cells

Question 21

Natural killer cells

Answer 21

Protect against cancer and virally infected cells; detect the downregulation of MHC and induced apoptosis

Question 22

Neutrophils

Answer 22

Most populous leukocyte in the blood and are very short-lived (a bit more than five days); phagocytic and target bacteria; can follow bacteria via chemotaxis; can also detect bacteria that have been opsonized; dead neutrophils = pus

Question 23

Eosinophils

Answer 23

Contain bright orange-red granules and are primarily involved in allergic reactions and invasive parasitic infections; release large amounts of histamine when activated; increased vasodilation and increased leakiness of the blood vessels, allowing additional immune cells (especially macrophages and neutrophils) to move out of the bloodstream and into the tissue; inflammation is particularly useful against extracellular pathogens including bacteria fungi, and viruses

Question 24

Basophils

Answer 24

Large purple granules and are involved in allergic reactions; least populous leukocyte in the bloodstream; mast cells are closely related to basophils but have smaller granules and exist in the tissues, mucosa, and epithelium; release large amounts of histamine in response to allergens, leading to inflammatory response

Question 25

What happens when an antigen binds to the surface of a mast cell?

Answer 25

Degranulation - exocytosis of granule contents, allowing the release of histamine and causing an inflammatory allergic reaction

Question 26

Hypermutation

Answer 26

B-cells undergo hypermutation of its antigen-binding region at the end of what is called the variable region (domain) at the tips of the Y

Question 27

Clonal selection

Answer 27

Only those B-cells that can bind the antigen with high affinity survive, providing a mechanism for generating specificity

Question 28

Constant region

Answer 28

The region that natural killer cells, macrophages, monocytes, and eosinophils have receptors for, and can initiate the complement cascade; note that each B-cell make only one type of antibody but we have many B-cells

Question 29

What are the five different isotypes of antibodies?

Answer 29

IgM, IgD, IgG, IgE, and IgA

Question 30

Isotype switching

Answer 30

Cells can change which isotype of antibody they produce when stimulated by specific cytokines

Question 31

Primary response

Answer 31

Initial activation takes 7-10 days

Question 32

Secondary response

Answer 32

More rapid and robust due to memory cells

Question 33

Positive selection

Answer 33

Maturing only cells that can respond to the presentation of antigen on MHC (cells that cannot respond to MHC undergo apoptosis because they will not be able to respond in the periphery)

Question 34

Negative selection

Answer 34

Causing apoptosis in cells that are self-reactive (activated by proteins produced by the organism itself)

Question 35

Thymosin

Answer 35

Peptide hormone secreted by thymic cells that facilitates maturation of T-cells ; once the T-cell has left the thymus, it is mature but naive; upon exposure to antigen, T-cells will also undergo clonal selection so that only those with the highest affinity for a given antigen proliferate

Question 36

Helper T-cells

Answer 36

CD4+ T-cells; coordinate the immune response by secreting chemicals known as lymphokines - molecules capable of recruiting other immune cells (plasma cells, cytotoxic T-cells, and macrophages) and increasing their activity

Question 37

HIV

Answer 37

Human immunodeficiency virus infection; prevents the immune system from mounting an adequate response to infection; loss of CD4+ cells

Question 38

AIDS

Answer 38

Acquired immunodeficiency syndrome; even weak pathogens can cause devastating consequences as opportunistic infections

Question 39

What stimulates CD4+ cells?

Answer 39

CD4+ T-cells respond to antigens presented on MHC-II molecules; MHC-II presents exogenous antigens, CD4+ T-cells are most effective against bacterial, fungal, and parasitic infections

Question 40

Cytotoxic T-cells

Answer 40

CTL or Tc cells or CD8+ T-cells are capable of directly killing virally infected cells by injecting toxic chemicals that promote apoptosis into the infected cell; CD8+ T-cells respond to antigens presented on MHC-I molecules - endogenous antigens; CD8+ T-cells are most effective against viral (and intracellular bacterial or fungal) infections

Question 41

Suppressor or regulatory T-cells

Answer 41

Also express CD4 but can be differentiated from helper T-cells because they also express a protein called Foxp3; cells help to tone down the immune response once infection has been adequately contained; also turn off self-reactive T lymphocytes to prevent autoimmune disease - self tolerance

Question 42

Memory T-cells

Answer 42

Cells lie in wait until the next exposure to the same antigen; when activated, they result in a more robust and rapid response

Question 43

Bacterial (Extracellular) infections

Answer 43

1) Macrophages and other APCs engulf the bacteria and subsequently release inflammatory mediators and present antigens on their surface (MHC-II)
2) Cytokines attract inflammatory cells, including neutrophils and additional macrophages
3) Mast cells are activated by the inflammation and degranulate, resulting in histamine release and increased leakiness of capillaries
4) Allows immune cells to leave the bloodstream to travel to the affected tissue
5) Dendritic cells then leave the affected tissue and travels to the nearest lymph node where it presents the antigen to B-cells
6) B-cells that produce the correct antibody proliferate through clonal selection to create plasma cells and memory cells - antibodies then travel through the bloodstream to the affected tissue, where they tag the bacteria for destruction
7) Dendritic cells also activate T-cells (particularly CD4+ cells) - two types: Th1 cells release interferon gamma which activates macrophages and increases their ability to kill bacteria and Th2 cells which help activate B-cells

Question 44

Viral (intracellular pathogen) infections

Answer 44

The virally-infected cell will begin to produce interferons, which reduce the permeability of nearby cells (decreasing the ability of the virus to infect these cells), reduce the rate of transcription and translation in these cells (decreasing the ability of the virus to multiple_ and cause systemic symptoms (malaise, muscle aching, fever, and so on); these infected cells also present intracellular proteins on their surface in conjunction with MHC-I; CD8+ T-cells will recognize the MHC-I and antigen complex as foreign and will inject toxins into the cell to promote apoptosis; the infection can be shut down before it is able to spread to nearby cells; natural killer cells will recognize the absence of MHC-I and will accordingly cause apoptosis of this cell

Question 45

Self-antigens

Answer 45

Proteins and carbohydrates present on the surface of every cell of the body; under normal conditions, these self-antigens signal to immune cells that the cell is not threatening and should not be attacked; when the immune system fails to make the distinction between self and foreign, it may attack cells expressing particular self-antigens - autoimmunity

Question 46

Hypersensitivity reactions

Answer 46

Allergies and autoimmunity

Question 47

Active immunity

Answer 47

The immune system is stimulated to produce antibodies against a particular pathogen; natural exposure - antibodies are generated by B-cells once an individual becomes infected; artificial exposure - vaccines with a weakened or killed form of the microbe or a part of the microbe’s protein structure

Question 48

Passive immunity

Answer 48

Transfer of antibodies to an individual

Question 49

Lymph nodes

Answer 49

Small, bean-shaped structures along the lymphatic vessels; contain a lymphatic channel as well as an artery and a vein; the lymph nodes provide a space for the cells of the immune system to be exposed to possible pathogens

Question 50

Functions of the lymphatic system

Answer 50

1) Equalization of fluid distribution - net pressure drawing fluid into the vessel at the venule end is slightly less than the the net pressure pushing fluid out at the arterial end; lymphatic vessels drain these tissues and subsequently return the fluid to the bloodstream (prevents edema)
2) Transportation of biomolecules - the lymphatic system transports fats from the digestive system into the bloodstream
3) Immunity

Question 51

Germinal center

Answer 51

Site where B-cells proliferate and mature in the lymph nodes in collections