This document summarizes the key components of cellular immunity, including adaptive and innate immunity. It describes the properties of immunity, such as specificity and memory. The major topics covered are cytokines, MHC proteins, lymphocytes, antigen presentation, T cell activation, and B cell activation. Adaptive immunity involves cell-mediated responses by T cells and antibody-mediated responses by B cells. Innate immunity provides genetically determined defenses.

1. HS 345: HUMAN PHYSIOLOGY
WILMINGTON COLLEGE
LISA REGULA MEYER
Cellular Immunity

2. © 2012 Pearson Education, Inc.
Properties of Immunity
1. Specificity
2. Versatility
3. Memory
4. Tolerance

3. Immunity
Response to threats on an
individualized basis
Adaptive Immunity
Active Immunity Passive Immunity
Adaptive immunity is not present at birth; you
acquire immunity to a specific antigen only when
you have been exposed to that antigen or receive
antibodies from
another source.
Develops in response
to antigen exposure
Develops after
exposure to
antigens in
environment
Develops after
administration of
an antigen to
prevent disease
Conferred by
transfer of maternal
antibodies across
placenta or in
breast milk
Conferred by
administration of
antibodies to
combat infection
Naturally acquired
active immunity
Artificially induced
active immunity
Naturally acquired
passive immunity
Artificially induced
passive immunity
Genetically
determined−no
prior exposure or
antibody
production
involved
Innate Immunity
Produced by transfer
of antibodies from
another source

4. Adaptive Defenses
Cell-Mediated
Immunity
Direct Physical and
Chemical Attack
Antibody-Mediated
Immunity
Attack by Circulating
Antibodies
Destruction
of antigens
Phagocytes
activated
T cells
activated
Communication
and feedback
Antigen presentation
triggers specific
defenses, or an
immune response.
Activated B
cells give rise
to cells that
produce
antibodies.
Activated T cells find
the pathogens and
attack them through
phagocytosis or the
release of chemical
toxins.

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Major Components of Cellular Immunity
Cytokines
MHC proteins
Lymphocytes

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Cytokines
 Chemical messengers released by tissue cells
 To coordinate local activities
 To act as hormones to affect whole body
Functions of Cytokines
1. Stimulate T cell divisions
 Produce memory TH cells
 Accelerate cytotoxic T cell maturation
1. Attract and stimulate macrophages
2. Attract and stimulate activity of cytotoxic T cells
3. Promote activation of B cells

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Types of Cytokines
Interleukins
Lymphokines
Monokines
Chemokines
Interferons

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MHC Proteins
 The membrane glycoproteins that bind to antigens
 Genetically coded in chromosome 6
 The major histocompatibility complex (MHC)
 Differs among individuals
Antigen Presentation
T cells only recognize antigens that are bound to
glycoproteins in plasma membranes

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Class I MHC
 Found in membranes of all nucleated cells
 Pick up small peptides in cell and carry them to the surface
 T cells ignore normal peptides
 Abnormal peptides or viral proteins activate T cells to destroy
cell

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Class II MHC
 Found in membranes of antigen-presenting cells (APCs)
 Found in lymphocytes
 Inserted in plasma membrane to stimulate T cells

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Lymphocytes
Lymphoid Stem Cells
 Group 1
 Remains in bone marrow and develop with help of stromal cells
 Produces B cells and natural killer cells
 Group 2
 Migrates to thymus
 Produces T cells in environment isolated by blood–thymus
barrier

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T Cells make up 80% of circulating lymphocytes
Cytotoxic
 Attack cells infected by viruses
 Produce cell-mediated immunity
Memory
 Formed in response to foreign substance
 Remain in body to give “immunity”
Helper*
 Stimulate function of T cells and B cells
Suppressor*
 Inhibit function of T cells and B cells
*Regulatory T Cells control sensitivity of immune response

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Overview
Antigen presentation
Antigen recognition
T Cell activation
 Antigen binding
 Co-stimulation
T Cell proliferation
T Cell differentiation

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Cell-Mediated Immune Response
Antigen Presentation
 First step in immune response
 Extracted antigens are “presented” to lymphocytes
 Or attached to dendritic cells to stimulate lymphocytes
 Can be phagocytic or non-phagocytic antigen-presenting
cells

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 Phagocytic APCs
• Free and fixed
macrophages
 In connective tissues
• Kupffer cells
 Of the liver
• Microglia
 In the CNS
Non-phagocytic APCs
 Langerhans cells
 In the skin
 Dendritic cells
 In lymph nodes and
spleen

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Antigen Recognition
 Inactive T cell receptors
 Recognize Class I or Class II MHC proteins
 Recognize a specific foreign antigen
 Double recognition
 Binding occurs when MHC protein matches antigen

19. © 2012 Pearson Education, Inc.

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CD Markers
• CD8 Markers
 Found on cytotoxic T
cells and suppressor T
cells
 Respond to antigens on
Class I MHC proteins
• CD4 Markers
 Found on helper T cells
 Respond to antigens on
Class II MHC proteins

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Co-Stimulation
 For T cell to be activated, it
must be costimulated
 By binding to stimulating
cell at second site
 Which confirms the first
signal

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Proliferation and Differentiation
After activation, activated T cells enlarge and
multiply
Newly expanded population of T cells differentiate
into
 Cytotoxic T cells
 Memory T cells
 Regulatory T cells
 Suppressor T cells
 Helper T cells

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Activation of CD8 T Cells
Activation of CD8 T Cells
 Activated by exposure to antigens on MHC proteins
 One responds quickly
 Producing cytotoxic T cells and memory T cells
 The other responds slowly
 Producing suppressor T cells

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Cytotoxic T Cells
 Seek out and immediately
destroy target cells
1. Release perforin
 To destroy antigenic plasma
membrane
1. Secrete poisonous lymphotoxin
 To destroy target cell
1. Activate genes in target cell
 That cause cell to die

25. Antigen Recognition Activation and
Cell Division
Infected cell
Inactive
CD8
T cell
Viral or
bacterial antigen
Antigen recognition occurs
when a CD8 T cell encounters
an appropriate antigen on the
surface of another cell, bound
to a Class I MHC protein.
Antigen recognition results
in T cell activation and cell
division, producing active TC
cells and memory TC cells.
Active
TC cell
Memory
TC cells
(inactive)
Infected
cell
CD8
protein
Class I
MHC
T cell
receptor
CD8
T cell
Antigen
Costimulation
activates
CD8 T cell
Before activation
can occur, a
T cell must be
chemically or
physically
stimulated by
the abnormal
target cell.
Costimulation

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Activation of CD4 T Cells
 Active helper T cells (TH cells)
 Secrete cytokines
 Memory helper (TH) cells
 Remain in reserve
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28. Activation by Class I MHC proteins
Antigen bound to
Class I MHC protein
Indicates that the cell is infected
or otherwise abnormal
CD8 T Cells
Cytotoxic T Cells Memory TC Cells
Attack and destroy
infected and
abnormal cells
displaying antigen
Await
reappearance
of the antigen
Control or moderate
immune response by
T cells and B cells
Suppressor T Cells

29. Activation by Class II MHC proteins
Helper T Cells
Stimulate immune
response by
T cells and B cells
Await
reappearance
of the antigen
Memory TH Cells
CD4 T Cells
Indicates presence of pathogens,
toxins, or foreign proteins
Antigen bound to
Class II MHC protein

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B Cell Sensitization
 Corresponding antigens in interstitial fluids bind to B
cell receptors
 B cell prepares for activation
 Preparation process is sensitization
 During sensitization, antigens are:
 Taken into the B cell
 Processed
 Reappear on surface, bound to Class II MHC protein

31. © 2012 Pearson Education, Inc.
Helper T Cells
 Sensitized B cell is prepared for activation but needs helper T
cell activated by same antigen
B Cell Activation
 Helper T cell binds to MHC complex
 Secretes cytokines that promote B cell activation and division

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B Cell Division
 Activated B cell divides into:
 Plasma cells
 Memory B cells

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Plasma Cells
 Synthesize and secrete antibodies into interstitial fluid
Memory B Cells
 Like memory T cells, remain in reserve to respond to next
infection

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Pathologies of Cellular Immunity
HIV/AIDS
DiGeorge Syndrome
Wiskott-Aldrich syndrome

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Combines Responses to Viral Infection
 Similar to bacterial infection
 But cytotoxic T cells and NK cells are activated by contact
with virus-infected cells

37. BACTERIA
Phagocytosis by
macrophages and APCs
Antigen
presentation
Activation of
cytotoxic T cells
Activation of
helper T cells
Activation
of B cells
Antibody
production by
plasma cells
Destruction of
bacteria by
cell lysis or
phagocytosis
Opsonization
and phagocyte
attraction
Formation of
antigen−antibody
complexes
Defenses against bacteria involve phagocy-
tosis and antigen presentation by APCs.

38. Release of
interferons
Infection of
tissue cells
Appearance of antigen
in plasma membrane
Infection of or uptake
by APCs
VIRUSES
Antigen
presentation
Activation of
helper T cells
Activation
of B cells
Antibody
production by
plasma cells
Destruction of
viruses or
prevention of
virus entry into cells
Increased
resistance to
viral infection
and spread
Stimulation
of NK cells
Activation of
cytotoxic T cells
Destruction of
virus-infected cells
Defenses against viruses involves direct contact with virus-infected cells
and antigen presentation by APCs.