The Immune System

1
The Immune System
2
2 Divisions of Immunity in Humans and Other
Mammals

• I. Innate Immunity Non-Specific

II. Acquired immunity Specific
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A. Barrier Defenses
4
Skin
5
B. Cellular Defenses
Microbes/antigens
PHAGOCYTIC CELL
Vacuole
Lysosome containing enzymes
6
There are different types of phagocytic cells
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Fig. 43-7
Interstitial fluid
Adenoid
Adenoid
Tonsil
Tonsil
Blood capillary
Lymph nodes
Blood capillary
Lymph nodes
Spleen
Lymphatic vessel
Tissue cells
Spleen
Lymphatic vessel
Tissue cells
Peyers patches (small intestine)
Peyers patches (small intestine)
Appendix
Appendix
Lymphatic vessels
Lymph node
Masses of defensive cells
Lymph node
Masses of defensive cells
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D. Inflammatory Responses
Fig. 43-8-3
Pathogen
Splinter
Chemical signals
Macrophage
Fluid
Mast cell
Capillary
Phagocytosis
Red blood cells
Phagocytic cell
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II. Acquired immunitylymphocyte receptors
provide pathogen-specific recognition
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Fig. 43-9
B cells and T cells have receptor proteins
that can recognize and bind to antigens
Antigen- binding site
Antigen- binding site
Antigen- binding site



Plasma membrane
T cell
Cytoplasm of T cell
Cytoplasm of B cell
B cell
(b) T cell receptor
(a) B cell receptor
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B Cells
Class II MHC and processed antigen are displayed
Antigen-specific B cell receptor
Antigen
Antibodies (Immunoglobins)
B cell
Cytokines (Lymphokines)
Plasma cell
Activated helper T cell
bacteria
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T Cells
Resting cytotoxic T cell
Resting helper T cell
Cytokines Released by Helper T-Cells
Granule w/ destructive enzymes
Activated killer cell
Activated helper T cell
Activated when they encounter infected cells that
are presenting antigens
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Killer Cells Cytotoxic Ts
Killer cell
Target cell
Target-oriented granules
Surface contact
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Fig. 43-12
Antigen- presenting cell
Microbe
Infected cell
Antigen associates with MHC molecule
1
Antigen fragment
Antigen fragment
1
1
Class II MHC molecule
Class I MHC molecule
2
2
T cell receptor
T cell receptor
2
T cell recognizes combination
(a)
Cytotoxic T cell
(b)
Helper T cell
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Activation of B Cells to Make Antibody
Circulating antibody
Antigen
Antigen-presenting cell
Class II MHC and processed antigen are displayed
Antigen-specific B cell receptor
Antigen is processed
Antigen
Class II MHC
Cytokines
Antibodies
B cell
Activated helper T cell
Antigen-presenting cell
Plasma cell
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Fig. 43-14
Animation Role of B Cells
Antigen molecules

B cells that differ in antigen specificity
Antigen receptor
Antibody molecules
Clone of memory B cells
Clone of plasma cells
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Fig. 43-16
Humoral (antibody-mediated) immune response
Cell-mediated immune response
Key
Antigen (1st exposure)
Stimulates Gives rise to

Engulfed by
Antigen- presenting cell



B cell
Helper T cell
Cytotoxic T cell


Memory Helper T cells



Antigen (2nd exposure)
Memory Cytotoxic T cells
Active Cytotoxic T cells

Plasma cells
Memory B cells
Secreted antibodies
Defend against extracellular pathogens by binding
to antigens, thereby neutralizing pathogens or
making them better targets for phagocytes and
complement proteins.
Defend against intracellular pathogens and cancer
by binding to and lysing the infected cells or
cancer cells.
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Helper T Cells
Fig. 43-17
Antigen- presenting cell
Peptide antigen
Bacterium
Class II MHC molecule
CD4
TCR (T cell receptor)
Helper T cell

Cytokines
Humoral immunity (secretion of antibodies
by plasma cells)

Cell-mediated immunity (attack on infected cells)


B cell
Cytotoxic T cell
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Fig. 43-18-3
Released cytotoxic T cell
Cytotoxic T cell
Perforin
Granzymes
CD8
TCR
Dying target cell
Class I MHC molecule
Pore
Target cell
Peptide antigen
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Fig. 43-19
Bacterium
Antigen-presenting cell
Peptide antigen
B cell
Class II MHC molecule
Clone of plasma cells
Secreted antibody molecules

Cytokines
TCR
CD4
Endoplasmic reticulum of plasma cell
Activated helper T cell
Helper T cell
Clone of memory B cells
2 µm
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Fig. 43-21
Viral neutralization
Opsonization
Activation of complement system and pore formation
Bacterium
Complement proteins
Virus
Formation of membrane attack complex
Flow of water and ions
Macrophage
Pore
Foreign cell