Chapter 44 – The Immune System: Internal Defense
Immune Response
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Body’s defensive responses against pathogens, toxins, other harmful agents
Recognize foreign or dangerous macromolecules
Respond to block entry, neutralize, and destroy.
Immunity: Definitions
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Immunity: immunis (latin) – “to make safe”
o Maintain an internal environment that allows us to maintain homeostasis
Pathogen: Disease producing organism
Antigen: foreign protein or molecules that initiate a response
Antibodies: defensive proteins produced by plasma cells (subpopulation of B-cells)
Some types of antigens
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Bacteria
o Extracellular: pneumonia and tetanus
o Intracellular: leprosy and tuberculosis
Viruses (flu and cold viruses)
Parasitic worms (helminthes)
o Stimulate eosinophils to respond
Abnormal body cells and virally infected cells
Human Immune Responses
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Pathogens invade tissues
o Rapid
 Nonspecific (innate) immune responses
 Skin; epithelial surfaces
o Physical barriers
o Antimicrobial peptides and other compounds
 Cytokines; chemokines
 Complement
 Phagocytes
o Phagocytosis
 Inflammation (both)
o Requires several hours to days
 Specific (adaptive) immune Responses – T cells and B Cells
 Cell mediated immunity
 Antibody mediated immunity
 Inflammation
Invertebrates and Vertebrates
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Invertebrates
o Nonspecific immune responses
 Physical, phagocytic, physiological and inflammatory
 Physical barriers (cuticle, epithelium)
 Phagocytosis
 Antimicrobial peptides (soluble,lyse membranes, destroy pathogens)
 Anything that destroys from a chemical standpoint.
Vertebrates
o Both nonspecific and specific immune responses
First-Line Defenses
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Physical barriers
o Skin
o Mucous linings of respiratory, digestive tracts
Antimicrobial peptides
o Produced by epithelial membranes
pH in stomach and acidic secretions onto surface of Skin
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Mucus
HCl may not necessarily destroy all pathogens in the digestive tract
Chemical Defenses
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Lysozyme in tears and saliva lyse bacterial walls
o Essentially punch holes in the surface of the bacterium causing them to have a chemical
imbalance and lyse.
Nonspecific Immune Cells
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Phagocytes destroy bacteria
o Neutrophils
o Macrophages
Natural Killer (NK) cells destroy cells infected with viruses
o Foreign or altered (tumor cells)
o In our system at all times
Cytokines
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Signaling proteins regulate interactions between cells
Interferons
o Inhibit viral replication
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o Activate natural killer cells
o Produced by cells that are virally infected
Tumor necrosis factor (TNF)
o Initiates inflammatory response
Interleukins
o Help regulate interactions between lymphocytes and other body cells
o Help mediate inflammation and fever
Chemokines
o Attract, activate, direct movement of certain immune system cells.
Complement Proteins
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Enhance inflammatory response
Lyse cell wall of pathogens
Coat pathogens (enhancing phagocytosis)
Attract white blood cells to site of infection
Refer to image in book – Pathogens invade Tissues
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Cells are injured
Activates molecules in plasma, mast cells, macrophages
o Vasodilation
 Increased blood flow to area
 Brings phagocytes, nutrients antibodies
 Redness
 Increased temperature
o Increased capillary permeability
 Antibodies pass from blood into inflamed area
 Edema pain
o Phagocytes migrate to region
 Increased phagocytosis
 Systemic Response
 Release TNF, IL-1
o Fever
Temperature (fever)
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A systemic response to mediators released at site of inflammation
Inhibits growth of many pathogens
Body temperature rises about 37.2C in response to pyrogens
Mobilizes defenses; accelerates repairs; inhibits pathogens
o Tends to decrease the ability of the invader to replicate
Acquired (adaptive, specific) immunity
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Acquired immunity – produced by prior exposure or antibody production
o Active immunity
 Produced by antibodies that develop in response to antigens (Immune response
 Naturally acquired immunity – develops after exposure to antigens in
environment
 Induced active immunity – develops after administration of antigen to
prevent diseases
o Passive Immunity
 Produced by transfer of antibodies from another person
 Induced passive immunity – conferred by administration of antibodies
to combat infection
 Natural passive immunity – conferred by transfer of maternal antibodies
across placenta or in breast milk
o Adaptive immunity involves specific cells called lymphocytes
Similarities in Animals and Human specific Immunity
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Specific (adaptive, acquired) response directed focused on individual organism or antigen
Molecular biology indicated adaptive (specific) immunity arose in jawed vertebrates as a result
of a viral infection
[My laptop died so I missed this last one]
Lymphatic System
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Living and nonliving components
Systemic (not localized) response
Defensive functions – neutralize and destroy
Non immune functions –
o Return excess interstitial fluid and filtered back to circulatory system
o Transport lipids absorbed from digestive tract to circulatory system.
Lymphatic system connects to all parts of the body
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Lymph nodes are accumulated in the axillary, groin, and jugular areas.
Lymphatic capillaries
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Flaplike – flaps are anchored so that as fluid pressure increases the flaps open. As fluid is
absorbed the flap closes
Not selective
Bone Marrow and Thymus are primary lymphoid organs
Site of cell development and immunocompetence
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Cells that migrate from the bone marrow to the thymus are called T-cells
Those that remain in the bone are B-Cells
Bone
o NK cells
o Macrophages
 Work with T cells – antigen presenting cells
o Monocyte
 Dendritic cells
 Work with T-cells – Antigen Presenting cells
o T-Cells
 Memory T cells
 T- cytotoxic cells
 T Helper cells – cooperate with B-Cells
 The last 2 are part of cell mediated immunity
o B-Cells
 Migrate to lymph nodes
 Plasma cell
 Memory Cell
Primary – where they’re produced
Secondary (peripheral) – organs and tissues
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Lymphocytes reside here and is where it makes contact with the antigen and mounts a response
Examples: spleen, lymph nodes, tonsils, payers patches (tissues in the intestine)
Immunocompetence
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Successful immune response require recognition of foreign organisms and substances
Is selection against T cells and B cells that recognize self and other cells that do not – those that
recognize self are destroyed
B-cells in bone marrow, T-cells in Thymus
Genetic rearrangement provides for ability to recognize a large number of different organisms
and antigens