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MCAT: Biology > Chapter 8: The Immune System > Flashcards

Chapter 8: The Immune System Flashcards

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1
Q

Differentiate innate and adaptive immunity.

A
  • Innate: composed of defenses that are always active against infection, but lack the ability to target specific invaders over others
  • Adaptive: defenses that target a specific pathogen, which is slower to act, but can maintain immunological memory
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2
Q

What structure produces all of the leukocytes that participate in the immune system through the process of hematopoiesis?

A

Bone marrow

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3
Q

What is the location of blood storage and activation of B-cells?

A

Spleen

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4
Q

What turns into plasma cells to produce antibodies as part of adaptive immunity?

A

B-cells

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5
Q

What is the thymus? Which cells mature in the thymus?

A
  • A small gland just in front of the pericardium, the sac that protects the heart
  • T-cells
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6
Q

What are the agents of cell-mediated immunity?

A

T-cells

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7
Q

What is the function of lymph nodes?

A
  • Provides a place for immune cells to communicate and mount an attack
  • They also filter lymph
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8
Q

What are the four components of the gut-associated lymphoid tissue (GALT)?

A
  • Tonsils
  • Adenoids
  • Peyer’s patches in the small intestines
  • Appendix
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9
Q

What are the three components of granulocytes? What is their precursor stem cell?

A
  • Neutrophils
  • Eosinophils
  • Basophils
  • Myeloid stem cell (precursor)
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10
Q

What are the functions of lymphocytes? Are they granulocytes or agranulocytes?

A
  • Responsible for antibody production, immune system modulation, and targeted killing of infected cells
  • Agranulocytes
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11
Q

What do monocytes become in tissues?

A

Macrophages

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12
Q

What is the difference between humoral immunity and cell-mediated immunity?

A
  • Humoral: B-cells and antibodies

- Cell-mediated: T-cells

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13
Q

What is the site of development of B-cells and T-cells?

A
  • B-cell: bone marrow

- T-cell: bone marrow

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14
Q

What is the site of maturation of B-cells and T-cells?

A
  • B-cell: bone marrow (but are activated in spleen or lymph nodes)
  • T-cell: thymus
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15
Q

What are the components of agranulocytes?

A

Include T-cells and B-cells (lymphocytes) and monocytes (macrophages)

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16
Q

What is our first line of defense?

A

Skin

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17
Q

What are the antibacterial enzymes found on the skin called?

A

Defensins

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18
Q

What mechanism do the respiratory passages possess to prevent pathogens from entering the body?

A

The respiratory tract has mucous membranes, lined with cilia to trap particulate matter and push it up toward the oropharynx, where it can be swallowed or expelled

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19
Q

What is lyzozyme?

A

Nonspecific bacterial enzyme secreted in tears and saliva

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20
Q

What are the two ways in which the GI tract plays a role in nonspecific immunity?

A
  • Stomach secretes acid, resulting in the elimination of most pathogens
  • The gut is colonized by bacteria, which compete with potential invaders, thus keeping them at bay
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21
Q

What is the complement system? What is their function?

A
  • Consists of a number of proteins in the blood that act as a nonspecific defense against bacteria
  • Punch holes in the cell walls of bacteria, making them osmotically unstable
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22
Q

What are the two ways in which the complement system can be activated?

A
  • Classical pathway: requires the binding of an antibody to a pathogen
  • Alternative pathway: does not require antibodies
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23
Q

What are interferons?

A
  • Cells that have been infected with viruses produce interferons
  • Proteins that prevent viral replication and dispersion
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24
Q

What do interferons upregulate? What is the result?

A
  • Upregulate MHC class I and II molecules

- Results in increased antigen presentation and better detection of the infected cells by the immune system

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25
Q

What is responsible for many “flu-like. symptoms that occur during viral infections?

A

Interferons

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26
Q

What are the three functions of an activated macrophage?

A

1) Phagocytizes the invader through endocytosis
2) Digests the invader using enzymes
3) Presents pieces of the invader to other cells using MHC

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27
Q

What does MHC do?

A

Binds to a pathogenic peptide (antigen) and carries it to the cell surface, where it can be recognized by cells of the adaptive immune system

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28
Q

What are cytokines? What releases cytokines?

A
  • Macrophages

- Chemical substances that stimulate inflammation and recruit additional immune cells to the area

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29
Q

Where is MHC-I found in? What proteins does it present? It allows the detection for what?

A
  • Found in all nucleated cells
  • Presents proteins created within the cell (endogenous antigens)
  • Allows the detection of cells infected with intracellular pathogens (especially viruses)
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30
Q

Where is MHC-II found in? What proteins does it present? It allows the detection for what?

A
  • Found in antigen-presenting cells (macrophages, dendritic cells)
  • Presents proteins that result from the digestion of extracellular pathogens that have been brought in by endocytosis (exogenous antigens)
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31
Q

What are pattern recognition receptors (PRR)? What cells possess PRR? What is the best-described?

A
  • Special receptors that are able to recognize the category of the invader (bacterium, virus, etc.)
  • Macrophages and dendritic cells
  • Toll-like receptor
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32
Q

What are dendritic cells?

A

Antigen-presenting cells in the skin

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33
Q

What are natural killer cells?

A

Attack cells not presenting MHC molecules, including virally infected cells and cancer cells

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34
Q

What is the most populous leukocyte in blood that is very short-lived?

A

Neutrophils

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35
Q

What are neutrophils? How do they follow bacteria?

A
  • Ingest bacteria, particularly opsonized bacteria (those marked with antibodies)
  • They follow bacteria using chemotaxis
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36
Q

What is an opsonized bacteria?

A

Marked with an antibody from a B-cell

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37
Q

What cells can attack opsonized bacteria?

A
  • Natural killer cells
  • Neutrophils
  • Macrophages
  • Monocytes
  • Eosinophils
38
Q

What are dead neutrophil collections responsible for?

A

For the formation of pus during an infection

39
Q

How does histamine cause inflammation?

A

By inducing vasodilatation and the movement of fluid and cells from the bloodstream into tissues

40
Q

What are eosinophils?

A
  • Used in allergic reactions and invasive parasitic infections
  • Release histamine, causing an inflammatory response
  • Red-orange granules
41
Q

What are basophils?

A
  • Large purple granules

- Involved in allergic responses by releasing histamine

42
Q

What are mast cells?

A

Involved in allergic responses by releasing histamine

43
Q

How do mast cells differ from basophils?

A

They have smaller granules and exist in the tissues, mucosa, and epithelium

44
Q

______ immunity involves the production of antibodies.

A

Humoral

45
Q

What are the three main possibilities for antibodies secreted into body fluids?

A

1) Once bound to a specific antigen, antibodies may attract other leukocytes to phagocytize those antigens (opsonization)
2) Antibodies may cause pathogens to agglutinate, forming large insoluble complexes that can be phagocytized
3) Antibodies can block the ability of a pathogen to invade tissues, essentially neutralizing it

46
Q

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

A
  • Causes degranulation (exocytosis of granule contents)

- Release of histamine, which causes an allergic reaction

47
Q

What are antibodies made of? What is their structure?

A
  • Y-shaped molecules
  • Two identical heavy chains
  • Two identical light chains
48
Q

What holds the antibody chains together?

A

Disulfide bonds and non-covalent interactions

49
Q

Where is the antigen-binding region on an antibody?

A
  • At the end of the variable region (domain)

- At the tips of the Y

50
Q

What happens when the antigen-binding region is activated?

A

The region undergoes hypermutation to improve the specificity of the antibody produced

51
Q

Which cells have the constant region? What can their receptors initiate?

A
  • Natural killer cells, macrophages, monocytes, eosinophils

- Can initiate the complement cascade

52
Q

How many isotopes do antibodies contain? What are they?

A
  • 5

- IgM, IgD, IgG, IgE, IgA

53
Q

What is isotype switching?

A

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

54
Q

Upon exposure to the correct antigen, B-cells will proliferate and produce two types of daughter cells. Differentiate them.

A
  • Plasma cells produce large amounts of antibodies

- Memory cells stay in the lymph node, awaiting reexposure to the same antigen

55
Q

What is primary response? How long does it last?

A
  • Activation of B-cells by the correct antigen, and proliferation into plasma cells and memory cells
  • 7 to 10 days
56
Q

What is secondary response?

A

Memory B-cells wait for a second exposure to a pathogen and can then mount a more rapid and vigorous immune response

57
Q

What is positive selection?

A
  • Only selecting for T-cells that can react to antigen presented on MHC
  • Cells that cannot respond to MHC undergo apoptosis
58
Q

What is negative selection?

A

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

59
Q

What is the maturation of T-cells facilitated by?

A

Thymosin, a peptide hormone secreted by thymic cells

60
Q

What are the three major types of T-cells?

A
  • Helper T-cells
  • Suppressor T-cells
  • Killer (cytotoxic) T-cells
61
Q

What are helper T-cells also called? What do they respond to?

A
  • CD4+ T-cells
  • Respond to antigens presented on MHC-II molecules
  • Because MHC-II presents exogenous antigens, CD4+ T-cells are most effective against bacterial, fungal, and parasitic infections
62
Q

How do helper T-cells coordinate the immune response?

A

By secreting chemicals known as lymphokines, which are capable of recruiting other immune cells and increasing their activity

63
Q

What is the consequence in terms of immunity of acquired immunodeficiency syndrome (AIDS)?

A

The loss of helper T-cells prevents the immune system from mounting an adequate response to infection

64
Q

Differentiate CD4+ T-cells and CD8+ T-cells.

A
  • CD4+ T-cells are better at fighting extracellular infections
  • CD8+ T-cells are better at targeting intracellular infections
65
Q

What are cytotoxic T-cells also called? What do they respond to?

A
  • CD8+ T-cells
  • Respond to antigens presented on MHC-I molecules
  • Because MHC-I presents endogenous antigens, they are most effective against viral (and intracellular bacterial or fungal) infections
66
Q

How do cytotoxic T-cells kill infected cells?

A

Directly kill virally infected cells by injecting toxic chemicals that promote apoptosis into the infected cell

67
Q

What is the mnemonic to differentiate CD4+ and CD8+ cells?

A
  • CD x MHC = 8
  • CD4+ x MHC-II = 8
  • CD8+ x MHC-I = 8
68
Q

What is the function of suppressor or regulatory T-cells?

A

Tone down the immune response after an infection and promote self-tolerance (turn off reactive lymphocytes to prevent autoimmune diseases)

69
Q

How do suppressor T-cells resemble helper T-cells? How are they different?

A
  • Also express CD4

- But, they also express a protein called Foxp3

70
Q

What are the five types of infectious pathogens?

A
  • Bacteria
  • Viruses
  • Fungi
  • Parasites (protozoa, worms, insects)
  • Prions (for which there are no immune defenses)
71
Q

What happens in autoimmune conditions?

A

A self-antigen is recognized as foreign, and the immune system attacks normal cells

72
Q

What happens in allergic reactions?

A

Non-threatening exposures incite an inflammatory response

73
Q

What happens in a bacterial (extracellular pathogen) infection?

A

1) Macrophages (and other APCs) engulf the bacteria and release inflammatory mediators, while presenting antigens on MHC-II
2) The cytokines attract inflammatory cells (neutrophils, macrophages)
3) Mast cells are activated and degranulate, releasing histamine and increased leakiness of the capillaries
4) Dendritic cell travels to the nearest lymph node, where it presents the antigen to B-cells
5) B-cells proliferate to create plasma and memory cells –> antibodies travel to the tissue where they tag bacteria for destruction
6) Dendritic cells also present the antigen to T-cells, activating T-helper cells in particular

74
Q

What is the difference between the two T-helper cells?

A
  • Th1 cells release interferon gamma (IFN-gamma), which activates macrophages and increases their ability to kill bacteria
  • Th2 cells help activate B-cells
75
Q

What happens in a viral (intracellular pathogen) infection?

A

1) The virally infected cell produces interferons
2) Present intracellular proteins on MHC-I
3) Cytotoxic T-cells respond to MHC-I and inject toxins to promote apoptosis

76
Q

What are the three consequences of virally infected cells producing interferons?

A
  • 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
  • Cause systemic symptoms (malaise, fever)
77
Q

What happens if a virus downregulates the production and presentation on MHC-I molecules?

A

Natural killer cells recognize the absence of MHC-I and will accordingly cause apoptosis

78
Q

What are self-antigens?

A

Proteins and carbohydrates present on the surface of every cell of the body

79
Q

What is active immunity?

A

Activation of B-cells that produce antibodies to an antigen prior to exposure of a particular pathogen

80
Q

What is passive immunity?

A

The transfer of antibodies to an individual

81
Q

What is natural active immunity? What is artificial active immunity?

A
  • Natural: antibodies are generated through infection

- Artificial: vaccinations

82
Q

What is natural passive immunity? What is artificial passive immunity?

A
  • Natural: transfer of antibodies from a mother’s milk to her baby
  • Artificial: transfer of antibodies intravenously
83
Q

What are the three main effects circulating antibodies can have on a pathogen?

A

1) Mark a pathogen for destruction by phagocytes (opsonization)
2) Cause agglutination of the pathogen in insoluble complexes that are taken up by phagocytes
3) Neutralize the pathogen by preventing its ability to invade tissues

84
Q

Where does lymphatic fluid enter the circulatory system?

A

Via the thoracic duct in the posterior chest, which then delivers fluid into the left subclavian vein (near the heart)

85
Q

What is the lymphatic system made of?

A

One-way vessels that become larger as they move toward the center of the body

86
Q

What are lymph nodes?

A

Small, bean-shaped structures, which contain a lymphatic channel, an artery, and a vein

87
Q

How does the lymphatic system prevent edema?

A
  • When the oncotic pressure of the blood is decreased, less water is driven into the bloodstream at the venule end
  • Fluid will collect in the tissues, but it may eventually return to the bloodstream via the lymphatics
88
Q

What is the function of the lymphatic system in terms of the transportation of fats?

A
  • Lacteals are located at the center of each villus in the small intestine
  • The fats packaged into chylomicrons enter the lacteal for transport
89
Q

Lymphatic fluid carrying many chylomicrons takes on a milky white appearance and is called ______.

A

chyle

90
Q

B-cells proliferate and mature in the lymph nodes in collections called ________.

A

germinal centers

MCAT: Biology (12 decks)

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