chapter 43 the immune system a macrophage engulfing bacteria
TRANSCRIPT
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Chapter 43
The Immune System
A macrophage engulfing bacteria
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Smallpox virus
The Body’s Defenses
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Anthrax bacteria
The Body’s Defenses
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Protozoan Trypanosoma
(African sleeping sickness)
The Body’s Defenses
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Sac fungus Candida albicans
(yeast infections)
The Body’s Defenses
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Heartworm nematodes...
The Body’s Defenses
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How does the human body defend against invaders?
INNATE IMMUNITY Rapid responses to a
broad range of microbes
ACQUIRED IMMUNITYSlower responses to
specific microbes
External defenses Internal defenses
Skin
Mucous membranes
Secretions
Phagocytic cells
Antimicrobial proteins
Inflammatory response
Natural killer cells
Humoral response(antibodies)
Cell-mediated response(cytotoxic lymphocytes)
Invadingmicrobes
(pathogens)
Figure 43.2
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Skin is an inhospitable barrier of dead, dry cells, & secretions containing oil & lactic acid
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Mucous membranes in respiratory, digestive & urogenital tracts secrete mucus & antibiotic chemicals (e.g., lysozyme,
which digests bacterial cell walls)
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How does the human body defend against invaders?
INNATE IMMUNITY Rapid responses to a
broad range of microbes
ACQUIRED IMMUNITYSlower responses to
specific microbes
External defenses Internal defenses
Skin
Mucous membranes
Secretions
Phagocytic cells
Antimicrobial proteins
Inflammatory response
Natural killer cells
Humoral response(antibodies)
Cell-mediated response(cytotoxic lymphocytes)
Invadingmicrobes
(pathogens)
Figure 43.2
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If external defenses are not effective – nonspecific, innate response
E.g., macrophages, dendritic cells
Four types of phagocytic leucocytes (WBCs) engulf invaders
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If external defenses are not effective – nonspecific, innate response
Microbes
VacuoleLysosome
Macrophage
Figure 43.4
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Natural killer cells (WBCs) – destroy infected cells & cancer cells by inducing
apoptosis (programmed cell death)
If external defenses are not effective – nonspecific, innate response
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Antimicrobial proteins – (e.g., lysozyme) produced by many cells of the body, often in response to infection; actively destroy
microbes
If external defenses are not effective – nonspecific, innate response
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Local inflammatory response – injury or pathogens can cause mast cells of
connective tissues to release histamine, triggering dilation and increased
permeability of capillaries
If external defenses are not effective – nonspecific, innate response
Fever – systemic (widespread) response that increases the body’s thermostat
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How does the human body defend against invaders?
INNATE IMMUNITY Rapid responses to a
broad range of microbes
ACQUIRED IMMUNITYSlower responses to
specific microbes
External defenses Internal defenses
Skin
Mucous membranes
Secretions
Phagocytic cells
Antimicrobial proteins
Inflammatory response
Natural killer cells
Humoral response(antibodies)
Cell-mediated response(cytotoxic lymphocytes)
Invadingmicrobes
(pathogens)
Figure 43.2
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ImmuneImmune
SystemSystem
Circulatory
System
Lymphatic
System
Immune system – mounts attack on specific disease agents
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2 main types of lymphocytes (WBCs):
B cells – produced in bone marrowdifferentiate in bone marrow
T cells – produced in bone marrowdifferentiate in thymus
Immune system – mounts attack on specific disease agents
Mature B and T cells are found throughout the body in lymph and blood
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2 main types of lymphocytes (WBCs):
Immune system – mounts attack on specific disease agents
Bone marrowLymphoid
stem cell
B cell
Blood, lymph, and lymphoid tissues
T cell
Thymus
Figure 43.10
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Lymphocytes recognize and respond to particular microbes and foreign molecules, i.e.,
they display specificity
A foreign molecule that induces an
immune response is known as an
antigen
RECOGNITION
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RECOGNITION
Fig. 43.7
Multiple antibodies may recognize the same antigen by different epitopes (small accessible portions
of the larger molecule)
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B cells produce antibodies, that are either secreted out of the cells or remain embedded in the B cell
membranes, and that bind to antigens
RECOGNITION
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B cells produce antibodies, that are either secreted out of the cells or remain embedded in the B cell
membranes, and that bind to antigens
T cells have T-cell receptors, embedded in their cell membranes, that bind to antigens
RECOGNITION
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RECOGNITION
Even though many receptors (antibodies or T-cell receptors) encounter a given type of antigen, only the receptors that are compatible will bind to them
Fig. 43.12
Illustrated here for B cells, but the process for T cells is similar
This process is known as clonal selection
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Fig. 43.8
RECOGNITION Secreted antibodies con-stitute a group of proteins called immunoglobulins
Antibodies have 2 heavy chain and 2 light chain subunits
Each subunit has a constant region and a variable region
The variable region can bind to an antigen
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Construction of antibodies(and T-cell receptors)
Millions of antigens are recognized by randomly combining the protein products of hundreds of genes
RECOGNITION of non-self molecules
Card analogy: although there are only 52 cards in the deck, random combinations can produce an
enormous number of different hands
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Construction of antibodies
B
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Construction of antibodies
BB
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Construction of antibodies
B BB
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In a healthy immune system, as B and T cells mature they are destroyed by apoptosis if they attack self
molecules
RECOGNITION of self molecules
Healthy, mature B and T cells then have the capacity to distinguish self from non-self molecules
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Almost all cells in an individual human’s body have major histocompatibility complex (MHC)
glycoproteins embedded in their cell membranes
RECOGNITION of self molecules
Class I MHC molecules are found on almost every nucleated cell
Class II MHC molecules are restricted to a few specialized cells, including macrophages,
dendritic cells, B cells, etc.
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MHC glycoproteins migrate to the cellmembrane after they are produced
RECOGNITION of self molecules
MHC glycoproteins pick up molecules from the cytosol that are presented at the cell’s surface
T cells bind to MHC glycoproteins and the molecules they present
An individual’s own MHC glycoproteins, and molecules of its own body that the MHC glycoproteins present, are
treated as self
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However, T cells treat foreign molecules presented by MHC glycoproteins as antigens
RECOGNITION of non-self molecules
Fig. 43.9
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Cytotoxic T cells bind to cells that carry Class I MHC glycoproteins
RECOGNITION of non-self molecules
Fig. 43.9
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Helper T cells bind to cells that carry Class II MHC glycoproteins
RECOGNITION of non-self molecules
Fig. 43.9
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Fig. 43.12
ATTACK & MEMORY The B and T cells that recognize a given foreign
antigen produce two types of clones:effector cells (attackers) and memory cells
Illustrated here for B cells, but the process for T cells is similar
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ATTACK & MEMORY The B and T cells that first recognize a given foreign
antigen are short lived, whereas immune memory cells can have long lifetimes
Illustrated here for B cells, but the process for T cells is similar
Fig. 43.12
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Fig. 43.13
ATTACK & MEMORY Memory cells help produce a secondary immune
response that is faster, of greater magnitude, and of longer duration than the primary immune response
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ATTACK & MEMORY There are two types of immune response:
Humoral responseB cells and antibodies
Attack antigens that have not yet infected cells (toxins, bacteria, and viruses in body fluids)
Deactivate, coat, and clump antigens (which are then often engulfed and destroyed by macrophages)
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ATTACK & MEMORY There are two types of immune response:
Cell-mediated responseT cells
Attack antigens after they have entered cells, as well as fungi, protozoa, and parasitic worms
Activated T cells kill antigen-containing cells by creating pores in their cell membranes
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RECOGNITION, ATTACK, & MEMORY
Figure 43.14
Humoral response Cell-mediated response
First exposure to antigen
Antigens Dendritic cells Infected cells
Activate Activate Activate
Gives rise to Gives rise to Gives rise to
B cell HelperT cell
CytotoxicT cell
Plasmacells
MemoryB cells
Active and memory helperT cells
Memory cytotoxic
T cells
Active cytotoxic
T cells
Secrete antibodies that defend againstpathogens and toxins in extracellular fluid
Defend against infected cells, cancer cells, and transplanted tissues
Cytokinesactivate
Involves the activation and
clonal selection of B cells
Results in the production of
antibodies that circulate in the
blood and lymph
MHC II MHC I
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RECOGNITION, ATTACK, & MEMORY
Figure 43.14
Humoral response Cell-mediated response
First exposure to antigen
Antigens Dendritic cells Infected cells
Activate Activate Activate
Gives rise to Gives rise to Gives rise to
B cell HelperT cell
CytotoxicT cell
Plasmacells
MemoryB cells
Active and memory helperT cells
Memory cytotoxic
T cells
Active cytotoxic
T cells
Secrete antibodies that defend againstpathogens and toxins in extracellular fluid
Defend against infected cells, cancer cells, and transplanted tissues
Cytokinesactivate
Involves the activation and
clonal selection of cytotoxic T
cells
Cytotoxic T cells directly
destroy certain target cells
MHC II MHC I
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RECOGNITION, ATTACK, & MEMORY
Figure 43.14
Humoral response Cell-mediated response
First exposure to antigen
Antigens
Activate Activate Activate
Gives rise to Gives rise to Gives rise to
B cell HelperT cell
CytotoxicT cell
Plasmacells
MemoryB cells
Active and memory helperT cells
Memory cytotoxic
T cells
Active cytotoxic
T cells
Secrete antibodies that defend againstpathogens and toxins in extracellular fluid
Defend against infected cells, cancer cells, and transplanted tissues
Cytokinesactivate
A primary immune
response begins with the
first exposure to an antigen
A secondary immune
response begins with a re-exposure to an
antigen, and stimulates
memory cells
Dendritic cells Infected cells
MHC II MHC I
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Medical practices can augment our immune response by inhibiting invaders or
enhancing the immune response
Antibiotics Inhibit microbial reproduction
Potent agents of natural selection
Vaccines (weakened or dead microbes, or their toxins)
Stimulate development of memory cells = faster response to invasion
Selectively effective
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The immune system and blood types
Table 43.1
antigen antigen antigens
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Allergies
Exaggerated immune responses to otherwise benign substances
What happens when the immune system malfunctions?
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What happens when the immune system malfunctions?
1. Antibodies are produced
Fig. 43.20
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What happens when the immune system malfunctions?
1. Antibodies are produced 2. Stems of antibodies attach to mast cells, especially in the respiratory tract
Fig. 43.20
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What happens when the immune system malfunctions?
1. Antibodies are produced 2. Stems of antibodies attach to mast cells, especially in the respiratory tract
3. When antibodies attached to mast cells bind antigens, the mast cells release histamine, which causes inflammation
Fig. 43.20
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Autoimmune diseasesThe immune system lacks or loses its ability to
distinguish self vs. non-self molecules, i.e., it loses its self-tolerance and produces anti-self antibodies
What happens when the immune system malfunctions?
Rheumatoid arthritis (cartilage of joints)
Multiple sclerosis (mylein sheaths of neurons)
Insulin-dependent diabetes mellitus (insulin-secreting cells of the pancreas)
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What happens when the immune system malfunctions?
Severe Combined Immunodeficiency (SCID)
An inherited disorder
Acquired Immunodeficiency Syndrome (AIDS)
Caused by retroviruses (Human Immunodeficiency Viruses –
HIV) that especially infect helper T cells
Immunodeficiency diseasesInhibit effective immune response; either
inherited or acquired
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Adults and children estimated to be living with HIV as of the end of 2001
Western Europe
560,000560,000North Africa & Middle East
440,000440,000Sub-Saharan
Africa
28.1 28.1 millionmillion
Eastern Europe & Central Asia
1 million1 million
South & South-East Asia
6.1 million6.1 million
Australia & New Zealand
15,00015,000
North America
940,000940,000Caribbean
420,000420,000
Latin America
1.4 1.4 millionmillion
Total: 40 million
East Asia & Pacific
1 million1 million
What happens when the immune system malfunctions?
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Estimated number of deaths from AIDS during 2001
Western Europe
6,8006,800North Africa & Middle East
30,00030,000Sub-Saharan
Africa
2.3 2.3 millionmillion
Eastern Europe &Central Asia
23,00023,000East Asia & Pacific
35,00035,000South & South-East Asia
400,000400,000
Australia & New Zealand
120120
North America
20,00020,000Caribbean
30,00030,000
Latin America
80,00080,000
Total: 3 million
What happens when the immune system malfunctions?
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What happens when the immune system malfunctions?
HIV destroy helper T cells– Victims die from other diseases
The global AIDS epidemic
Transmission– Direct contact between broken skin, mucous membranes & body
fluids
No cure – Treatments = inhibitors of reverse-transcriptase and protease– Problem = virus evolves quickly
How to reduce your risk– Practice safe sex– Avoid used needles
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Cancer
Malfunction in cell production combined with a lack of recognition by the
immune system of aberrant cells or too many of them
Uncontrolled growth = tumor
What happens when the immune system malfunctions?
Causes
Carcinogens, viruses, inheritance
No guaranteed cure
Most treatments also destroy healthy cells
How to reduce your risk
Reduce exposure to carcinogens