1. Chapter 24 The Immune System
The human body’s immune system
recognizes agents that cause disease and
attacks them.
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2. INNATE IMMUNITY
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3. 24.1 All animals have innate immunity
Nearly everything in the environment teems with pathogens, agents that cause disease.
The immune system is the body’s system of defenses against agents that cause disease.
Innate immunity is a series of defenses that
act immediately upon infection and
are the same whether or not the pathogen has been encountered before.
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4. 24.1 All animals have innate immunity
Invertebrates rely solely on innate immunity, which may consist of
an exoskeleton,
low pH,
the enzyme lysozyme, and
immune cells capable of phagocytosis, cellular ingestion and digestion of foreign substances.
Vertebrates have innate and adaptive immunity.
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5. 24.1 All animals have innate immunity
Vertebrate innate immunity includes
barriers such as skin and mucous membranes,
interferons, proteins produced by virus-infected cells, that help to limit the cell-to-cell spread of viruses,
neutrophils (phagocytic cells),
macrophages, large phagocytic cells that wander through the interstitial fluid,
natural killer cells that attack cancer cells and virus-infected cells, and
a complement system, a group of about 30 kinds of proteins that can act with other defense mechanisms.
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6. Antiviral proteins block viral reproduction Virus
Figure 24.1B
Viral nucleic acid
Antiviral proteins block viral reproduction
Virus 1
New viruses 2
Interferon genes turn on
DNA
mRNA 3 5
Interferon molecules
Interferon stimulates cell to turn on genes for antiviral proteins
Figure 24.1B The interferon mechanism against viruses 4
Host cell 1
Host cell 2
Makes interferon; is killed by the virus
Is protected against the virus by interferon from cell 1 6

7. 24.2 Inflammation mobilizes the innate immune response
Tissue damage triggers the inflammatory response, a major component of our innate immunity, which can
disinfect and clean infected tissues and
limit the spread of infection to surrounding tissues.
Bacterial infections can bring about an overwhelming systemic inflammatory response leading to septic shock, characterized by
very high fever and
low blood pressure.
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8. Figure 24.2 The inflammatory response Neutrophil
Bacteria
Splinter
Signaling molecules
Macrophage
Neutrophil
Movement of fluid
Mast cell
Phagocytosis
Capillary
Red blood cells
Figure 24.2 The inflammatory response
Neutrophil 1
Tissue injury; signaling molecules are released from mast cells and macrophages that affect capillary cells. 2
Capillaries widen and become leaky. Neutrophils migrate to the infected area. 3
Neutrophils digest bacteria and cell debris at the site, and the tissue heals. 8

9. ADAPTIVE IMMUNITY
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10. 24.3 The adaptive immune response counters specific invaders
Our immune system responds to foreign molecules called antigens, which elicit the adaptive immune response. This is a complex biochemical system but essentially lymphocytes produce proteins called antibodies that destroy antigens
The adaptive immune system
is found only in the vertebrates,
reacts to specific pathogens, and
“remembers” an invader.
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11. 24.3 The adaptive immune response counters specific invaders
Infection or vaccination triggers active immunity.
Vaccination, or immunization, exposes the immune system to a vaccine,
a harmless variant or
part of a disease-causing microbe (antigen).
Lymphocytes make antibodies that destroy antigens
We can temporarily acquire passive immunity by receiving premade antibodies.
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12. 24.4 The lymphatic system becomes a crucial battleground during infection
The lymphatic system is
involved in innate and adaptive immunity and
consists of a network of
lymphatic vessels,
lymph nodes, and lymph, which is similar to blood plasma.
Lymph nodes occur throughout the body and include the spleen
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13. 24.4 The lymphatic system becomes a crucial battleground during infection
Lymphatic vessels
collect fluid from body tissues and
return it as lymph to the blood.
Lymph organs
include the spleen and lymph nodes and
are packed with white blood cells that fight infections.
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14. 24.4 The lymphatic system becomes a crucial battleground during infection
As lymph circulates through lymphatic organs it
collects
microbes,
parts of microbes, and
microbial toxins, and
transports them to lymphatic organs where
macrophages in lymphatic organs engulf the invaders and
lymphocytes may mount an adaptive immune response by forming antibodies.
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15. Figure 24.4
Organs
Adenoid
Lymphatic ducts that drain into veins
Lymph node
Tonsils
Lymph nodes
Masses of lymphocytes and macrophages
Thymus
Lymphatic vessels
Valve
Lymphatic vessel
Spleen
Blood capillary
Tissue cells
Interstitial fluid
Appendix
Bone marrow
Figure 24.3 The human lymphatic system
Lymphatic capillary 15