Chapter 43: The Immune System Flashcards

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1
Q

Innate vs. adaptive immunity

A

Innate immunity is common to all animals and is present from birth

Adaptive immunity is found only among vertebrates and develops after exposure to pathogens

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2
Q

Components of the innate immune system

A

Barrier defenses

Cellular innate defenses

Local inflammatory response

Antimicrobial peptides and proteins

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3
Q

Cellular innate defenses

A

Phagocytic cells dedicated to detecting, devouring, and destroying pathogens that include:

  • Neutrophils
  • Macrophages
  • Dendritic cells
  • Eosinophils
  • Natural killer cells
  • Mast cells

Many cellular involve the lymphatic system

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4
Q

Toll-like receptor

A

Found expressed on the surface of phagoctic cells or on the inner surface of vesicles formed by endocytosis

Binds to fragments of molecules characteristic of a set of pathogens to signal phagocytosis such as:

  • Double-stranded RNA characteristic of certain viruses
  • Lipoplysaccharides commonly found on the surface of baterium
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5
Q

Neutrophils

A

Phagocytic cells of the innate immune system that circulate in the blood and are attracted by signals from infected tissues

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6
Q

Macrophages

A

LARGER phagocytic cells of the innate immune system that stimulate adaptive immunity by presenting antigens that they engulf

Some migrate throughout the body while others are found in specific organs or tissues such as the spleen

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7
Q

Dendritic cells

A

Phagocytic cells of the innate immune system that stimulate adaptive immunity by presenting antigens that they engulf

Mainly populate tussues such as the skin that are in contact with the environment

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8
Q

Eosinophils

A

Phagocytic cells of the innate immune system that are defend against multicellular pathogens such as parasitic worms by discharging destructive enzymes

Often found beneath the epithelium

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9
Q

Natural killer cells

A

Phagocytic cells of the innate immune system that circulate through the body and detect abnormal surface proteins on some virus-infected and cancerous cells

Do NOT enfulf stricken cells but instead release chemicals that lead to cell death which inhibit the spread of virally infected or cancerous cells

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10
Q

Lymphatic system structures

A

Consists of lymphatic vessels and structures that trap foreign substances such as the lymph nodes and lymphoid organs:

  • Adenoids
  • Tonsils
  • Thymus
  • Spleen
  • Peyer’s patches- in small intestines
  • Appendix
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11
Q

Antimicrobial peptides and proteins

A

Function in innate defense by attacking pathogens or impeding their reproduction

  • Interferons
  • Complement system
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12
Q

Interferons

A

Proteins secreted by virus-infected cells that induce nearby uninfected cells to produce substances that inhibit viral replication

Limit cell-to-cell spread of viruses in the body

Control viral infections such as colds and influenza

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13
Q

Complement system

A

Consists of roughly 30 proteins in blood plasma that circulate in the inactive state and are activated by substances on the surface of many pathogens

Activation by antibodies results in a cascade of biochemical reactions that form pores in the membranes of target cells which lead to lysis of the invading cells

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14
Q

Local inflammatory response

A
  1. Begins when activated macrophages discharge cytokines that recruit neutrophils to the site of injury
  2. Mast cells release signaling molecule histamine that triggers nearby blood cessels to dilate and become more permeable
  3. Activated complement proteins promote further histamine release attracting more phagocytic cells
  4. Enhanced blood flow to the site helps deliver antimicrobial peptides that result in an accumulation of pus
  5. Pus and excess fluid are eventually taken up in lymph and transported to lymph nodes where pathogens are phagocytized by macrophages
  6. Dendridic cells are usually located outside of the lymphatic system but migrate to the lymph nodes after interacting with pathogens
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15
Q

Systemic inflammatory response

A

Cells in injured or infected tissue often secrete molecules that stimulate the release of additional neutrophils from the bone marrow

Fever can be induced in response to substances released by activated macrophages that cause the body’s thermostat to reset to a higher temperature

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16
Q

Primary components of the adaptive immune system

A

The adaptive response relies on two types of lymphocytes:

  • Those that mature in the thymus above the heart are called T cells
  • Those that mature in bone marrow are called B cells
17
Q

Epitope

A

A small accessible portion of an antigen that binds to an antigen receptor

18
Q

B cell antigen receptor

A

Y-shaped protein with two identical heavy chains and light chains linked together by three disulfide bridges

Each chain has a constant (C) region and a variable (V) region that recognizes a specific antigenic epitope

  • The constant region of the heavy chain contains a transmembrane region that anchors the receptor in the cell’s membrane

Each chain thus has two identical antigen binding sites

19
Q

Antigen recognition by B cells

A

Binding of the B cell antigen receptor to an antigen leads to the eventual secretion of a soluable, free-floating copy of the B cell antigen receptor called an antibody, also known as an immunoglobulin

Antibodies have the same Y-shapped structure as B cell antigen receptors but lack a membrane anchor

IgD is membrane bound while the other four, IgA, IgE, IgG, and IgM are soluble

20
Q

T cell antigen receptor

A

Rod-shaped protein with two different α and β chains linked together by one disulfide bridges

Each chain has a constant (C) region and a variable (V) region that recognizes a specific antigenic epitope

  • The variable region of both the α and β chain come together to form a single antigen binding site
  • The constant region of the heavy chain contains a transmembrane region that anchors the receptor in the cell’s membrane
21
Q

Antigen recognition by T cells

A

T cells bind only to fragments of antigens that are displayed or presented on the surface of host cells

Host protein that displays antigen fragment is called a major histocompatability complex (MHC) molecule

  • Class I MHC is found on all nucleated human cells; activate cytotoxic T cells
  • Class II MHC are found on macrophages, dendritic cells, and B cells; activate helper T cells

The display of protein antigen fragments occurs when a pathogen infects a host cell or when an immune cell engulfs a pathogen and degrades it

The T cell can then bind both the antigen fragment and the MHC molecule

22
Q

Lymphocyte development

B and T cells

A

Capacity to generate diversity is built into structure of Ig genes

Receptor chain is encoded by three gene segments: a variable (V), joining (J), and constant (C) segment

Alternative copies of the V and J segments are arrayed along the gene in a series can be rearranged to prodice a wide array of different chains

23
Q

Self-tolerance

A

As lymphocytes mature in bone marrow or the thymus they are tested for self-reactivity

Some B and T cells with receptors specific for the body’s own molecules are destroyed by apoptosis

The remaining self-reactive lymphocytes are typically rendered nonfunctional

24
Q

Clonal selection

A

Binding of of an antigen repeptor to a matching epitope activates the lymphocyte bearing the receptor

Once activated a B or T cell undergoes multiple cell divisions to produce a clone of identical cells

Some cells from the clone become effector cells that act immediately against the antigen

  • B cell effectors form plasma cells that secrete antibodies
  • T cell effectors form helper T cells and cytotoxic T celss

Some cells from the clone become long-lived memory cells that can give rise to effector cells if the same antigen is encountered again

25
Q

Immunological memory

A

Prior exposure to an antigen alters the speed, strength, and duration of the immune response

Primary response- slower onset; peaks about 10−17 days after initial exposure

Secondary response- faster onset; peaks about 2−7 days after exposure and is of greater magnitude and more prolonged

26
Q

Adaptive immune response

A

In the humoral immune response antibodies help neutralize or eliminate toxins and pathogens in the blood and lymph fluid

In the cell-mediated immune response specialized T cells destroy affected host cells

Both can include primary and secondary immune responses wiht memory cells enabling the secondary response

27
Q

Helper T cells

A

Trigger both the humoral and cell-mediated immune responses

The antigen must be displayed on the surface of an antigen presenting cell such as a dendridic cell, a macrophage, or a B cell

Antigen receptors on the helper T cell bind to the antigen fragment on the Class II MHC molecule

Simultaneously, an accessory CD4 protein binds to the Class II MHC molecule itself to help keep the cells joined

The helper T cell is activated, proliferates, and forms a clone of helper T cells, which then activate the appropriate B cells or cytotoxic T cells

28
Q

Cytotoxic T cells

A

Use toxic proteins to kill cells infected by viruses or other intracellular pathogens

Are activated by cytokines secreted by helper T cells and interaction with an infected antigen presenting cell

Antigen receptors on the cytotoxic T cell bind to the antigen fragment on the Class I MHC molecule

Simultaneously, an accessory CD8 protein binds to the Class I MHC molecule and triggers cytotoxic T cell activity

29
Q

Humoral activation of B cells

A

Activation of B cells involves stimulation by both helper T cells and pathogenic epitopes

B cells present antigens to which they have bound on Class II MHC proteins that are recognized by previously activated helper T cells

Activate helper T cells then secrete cytokines that lead to proliferation of the B cell and differentiation into memory B cells and antiody-secreting plasma cells

30
Q

Antibody function

A

Antibodies do not directly kill pathogens but mark them for destruction in a variety of ways:

  • In neutralization antibodies bind to viral surface proteins, preventing infection and entry into a host cell
  • In opsonization antibodies bind to epitopes on bacteria, triggering phagocytosis by macrophages or neutrophils
  • Antigen-antibody complexes may bind to a complement protein which triggers a cascade of complement protein activation
31
Q

Active vs. passive immunity

A

Active immunity develops naturally when a pathogen invades the body and elicits a primary or secondary immune response

  • Artificial active immunity develops following immunization

Passive immunity provides immediate, short-term protection conferred naturally when IgG crosses the placenta from mother to fetus or when IgA passes from mother to infant in breast milk

  • Artificial passive immunization occurs when antibodies from an immune animal are injected into a non-immune animal
32
Q

Immune rejection

A

Differences in MHC molecules stimulate rejection of tissue grafts and organ transplants

33
Q

Allergic reactions

A

IgE antibodies are produced after first exposure to an allergen attach to receptors on mast cells

The next time the allergen enters the body it binds to mast cell-associated IgE molecules and trigger the release of histamine and other mediators that cause typical allergy symptoms