The IMMUNE SYSTEM

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The IMMUNE SYSTEM

• AP Bio Chapter 43

Antibody Immune System Response - Medical
Animation
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http//www.youtube.com/watch?viVMIZy-Y3f8
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Organs of the Immune System
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Fig. 43-7
Interstitial fluid
Adenoid
Tonsil
Blood capillary
Lymph nodes
Spleen
Lymphatic vessel
Tissue cells
Peyers patches (small intestine)
Appendix
Lymphatic system
Lymphatic vessels
Lymph node
Masses of defensive cells
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The Lymphatic System

• The lymphatic system aids the immune system
  in removing and destroying waste, debris, dead
  blood cells, pathogens, toxins, and cancer cells.
  
• The lymphatic system absorbs fats and fat-soluble
  vitamins from the digestive system and delivers
  these nutrients to the cells of the body where
  they are used by the cells.
• The lymphatic system also removes excess fluid,
  and waste products from the interstitial spaces
  between the cells.

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What about the spleen?

• It acts as a filter for blood as part of the
  immune system. Old red blood cells are recycled
  in the spleen, and platelets and white blood
  cells are stored there.

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The immune system recognizes foreign bodies and
responds with the production of immune cells and
proteins
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• Two major kinds of defense have evolved
• innate immunity and
• acquired immunity

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• Innate immunity is present before any exposure to
  pathogens and is effective from the time of birth
• It involves nonspecific rapid responses to
  pathogens
• Innate immunity consists of external barriers
  plus internal cellular and chemical defenses

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• Acquired immunity, or adaptive immunity, develops
  after exposure to agents such as microbes,
  toxins, or other foreign substances
• It involves a very specific response to pathogens

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Fig. 43-2
Pathogens (microorganisms and viruses)
Barrier defenses Skin Mucous membranes Secretions
INNATE IMMUNITY
Recognition of traits shared by broad ranges of
pathogens, using a small set of receptors

Internal defenses Phagocytic cells Antimicrobial
proteins Inflammatory response Natural killer
cells

Rapid response
Humoral response Antibodies defend
against infection in body fluids.
ACQUIRED IMMUNITY

Recognition of traits specific to
particular pathogens, using a vast array of
receptors
Cell-mediated response Cytotoxic lymphocytes
defend against infection in body cells.

Slower response
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The IMMUNE SYSTEM
pathogens
skin
Innate response
Acquired response
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Innate immunity of vertebrates

• Physical
• Skin low pH of skin secretions
• Mucous membranes lining digestive, respiratory,
  genitourinary tracts trap and remove microbes
  (with cilia in resp)

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• Chemical
• Lysozyme enzymes that attack microbial walls,
  found in tears, saliva, and mucus
• Gastric juice low pH
• Interferons proteins produced by viral-infected
  cells to alert other cells to defend against
  viral reproduction also stimulates macrophages
• Complement proteins in plasma that when
  activated by microbial contact may lyse cells,
  trigger inflammation, or assist acquired
  defensive immunity

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Complement aiding the acquired immunity system
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• Cellular
• Macrophages attack microbes in the spleen and
  interstitial fluid (known as monocytes in the
  blood)
• Neutrophils most numerous phagocytizing cells,
  phagocytize bacteria
• Eosinophils attack multicellular parasites
• Dendritic cells in contact with environment,
  stimulate acquired immunity system
• Natural killer cells (NK cells) recognize
  absence of self-markers on infected cells

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macrophage
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Neutrophils first on the job
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Eosinophils attack multicellular parasites
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A dendritic cell
http//www.rockefeller.edu/interactive/steinman/de
ndritic_cell_v5.swf
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• Dendritic cell
• alerting the
• acquired
• immune
• system

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NK cell doing its job!
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What are toll-like receptors?

• TLRs are proteins that span membranes in
  leukocytes and other cells that recognize
  nonspecific microbes that breach physical
  barriers such as the skin or intestinal tract.
• They in turn activate the immune system.
• Originally identified in insects.

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TLRs spanning the membrane.
Response
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Toll-like receptors
Alert! Microbes entering!
http//www.youtube.com/watch?viVMIZy-Y3f8
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• Inflammatory response
• Redness, swelling, heat
• Damaged mast cells in connective tissue release
  histamine which triggers dilation and leakiness
  of blood vessels, activates macrophages, promotes
  blood flow to the area
• Fever triggered by toxins or pyrogens released
  by macrophages, stimulates production of wbcs,
  speeds tissue healing
• Septic shock overwhelming systemic inflammatory
  response

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Fig. 43-8-3
Pathogen
Splinter
Chemical signals
Macrophage
Fluid
Mast cell
Capillary
Phagocytosis
Red blood cells
Phagocytic cell
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ACQUIRED IMMUNITY (adaptive immunity)

• Job of lymphocytes that circulate in the blood
  and lymph, conc in spleen and lymph nodes
• Develop from pluripotent stem cells in the bone
  marrow and liver of fetuses
• Become T cells after cells have migrated to the
  Thymus or
• B cells that develop in the Bone marrow

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Where is the thymus gland?
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How do the B and T cells work with the innate
immune system?

• Signaling molecules (cytokines) from
  macrophages and dendritic cells activate them.

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What are antigens?

• Antigens proteins or polysaccharides protruding
  from microbes or toxins floating around
  (antibody-generating)
• Epitope (antigenic determinants) portion of the
  antigen recognized by immune cells

Looks like epitopes to me!
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Fig. 43-10
Antigen- binding sites
Epitopes (antigenic determinants)
Antigen-binding sites


Antigen
Antibody A
Antibody C
V
V
V
V
C
C
C
C
Antibody B
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How tricky are pathogens

• Antigenic variation changing their surface
  epitopes to be unrecognizable
• Some viruses go into a latency period and hide
  from the immune cells
• AIDS does both of these.

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There are millions of lymphocytes with their own
types of antigen receptors. How is the great
diversity of B and T cells produced?

• They are determined during early embryonic
  development by genetic recombination
• Receptors have constant regions and variable
  regions that are specific for antigens.

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Fig. 43-9a
Antigen- binding site
Antigen- binding site


Disulfide bridge
V
V
V
V
Variable regions
C
C
Constant regions
C
C
Light chain
Transmembrane region

Plasma membrane
Heavy chains
Cytoplasm of B cell
B cell
(a) B cell receptor
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Fig. 43-9b
Antigen- binding site

Variable regions
V
V
Constant regions
C
C
Transmembrane region

Plasma membrane
? chain
? chain
Disulfide bridge
T cell
Cytoplasm of T cell
(b) T cell receptor
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What prevents B and T cells from reacting against
the bodys own molecules?

• Lymphocytes with receptors specific for bodys
  own molecules are either inactivated or destroyed
  by apoptosis. This is called self-tolerance.

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How to distinguish self from nonself

• MHC molecules are so named because they are
  encoded by a family of genes called the Major
  Histocompatibility Complex They identify cells
  as belonging to you!
• (histo tissue)

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• Class I MHC molecules are found on almost all
  nucleated cells of the body
• Class II MHC molecules are found on immune cells
  such as dendritic cells, macrophages, and B
  cells.
• They digest antigens and display pieces of the
  antigen with their MHC complex and are called
  antigen-presenting cells (APCs).

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Class I body cells
Class II- immune cells
Once the cells engulf the antigens, they display
them on their MHC complexes SELF-NONSELF.
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• Cytotoxic-T cells will bind to the MHC I
  complexes (recognize infected cells)
• Helper T- cells will bind to the MHC II
  complexes. MHC II cells are called APCs
  (Antigen Presenting Cells).

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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 I MHC molecule
Class II 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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Immunological Memory

• When antigens react with the immune cells, the
  cells that are specific for that antigen are
  activated to divide repeatedly and differentiate
  into clones
• Effector cells combative cells
• Memory cells which carry receptors for that
  particular antigen
• This is called CLONAL SELECTION.

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Fig. 43-14
Antigen molecules

B cells that differ in antigen specificity
Antigen receptor
This one!
Clonal selection
Antibody molecules
Clone of memory cells
Clone of plasma cells
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Monoclonal Antibody Production
Monoclonal Antibody Production
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• The first exposure to a specific antigen
  represents the primary immune response
• During this time, effector B cells called plasma
  cells are generated, and T cells are activated to
  their effector forms
• In the secondary immune response, memory cells
  facilitate a faster, more efficient response

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Fig. 43-15
Primary immune response to antigen A
produces antibodies to A.
Secondary immune response to antigen A produces
antibodies to A primary immune response to
antigen B produces antibodies to B.
104
103
Antibody concentration (arbitrary units)
Antibodies to A
Antibodies to B
102
101
100
0
7
14
21
28
35
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Exposure to antigen A
Exposure to antigens A and B
Time (days)
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Remembering the antigen!
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Vaccines stimulate a mild primary response so
body can wage a secondary response to recognize
another attack.
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Acquired Immunity 2 types Humoral and
Cell-mediated

• Humoral Immune Response (antibody-mediated
  response)
• involves B cells and
• production of antiBodies in response to
  free-floating antigens or those on surface of
  foreign cells

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B cells mature into plasma cells that produce
antibodies.
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• Cell-mediated Response
• involves cytotoxic T cells that destroy target
  infected cells

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The central role of Helper-Ts

• Immune cells (class II MHC) engulf antigens and
  display them on their MHC.
• Specific helper-Ts recognize the MHC-antigen
  complex.

Binding to the helper-T
Displaying the antigen
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• A T-cell surface protein called CD4 binds the
  helper-T to the MHC-II.
• Activated helper-Ts release cytokines
  (interleukins)
• - result in more specific help-Ts and
  memory cells being produced.
• - stimulate both cell-mediated and
  humoral responses

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The central role of Helper-Ts
Fig. 43-17
Antigen- presenting cell
Peptide antigen
Binds
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
Animation The Immune Response
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Cell-mediated Response, how?

• When a nucleated regular cell becomes infected,
  pieces of antigens are combined with the MHC I
  and they bond to cytotoxic T cells with the help
  of CD8 surface proteins.
• The cytotoxic cell becomes a killer cell which
  releases perforin that punches holes in the
  infected cell.

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• CD 8s and CD 4s are like bungy cords.

They hold the MHC to the T or B cells
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Cell Mediated ImmunityResponse of Cytotoxic T
cells
Cytotoxic T-cell Activity Against Target Cells
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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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Humoral Response, how?

• The B cell takes in a few foreign molecules and
  presents antigen fragments in its class II MHC to
  activated helper-T cells.
• The activated B cell then proliferates into a
  clone of plasma cells that will produce
  antibodies and a clone of memory B cells. (Some
  do not require T-cell binding or cytokines.)

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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

TCR
CD4
Cytokines
Endoplasmic reticulum of plasma cell
Activated helper T cell
Helper T cell
Clone of memory B cells
2 µm
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Humoral ImmunityT-Cell Dependent Antigens
Interaction of Antigen Presenting Cells and
T-helper Cells
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The cartoon illustrates how an antibacterial
antigen-specific immune response is generated.
Microbes invade the body and are captured by
dendritic cells (DCs, the policemen). The DC
presents the antigen to the B and Th cells.
The B cells respond by bombing the microbes
with antibodies.
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Putting it all together
http//highered.mcgraw-hill.com/sites/0072495855/s
tudent_view0/chapter24/animation__the_immune_respo
nse.html
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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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Hematopoetic stem cells in bone marrow
differentiate
Cells present in
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Types of Antibodies

• Antibodies are proteins that are made of light
  and heavy chains.
• There are 5 different antibodies IgM, IgG, IgA,
  IgD, and IgE. IgG is the most abundant.
• IgE antibodies involved in allergies

Respond to Different antigens
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IgE Mediated Hypersensitivity

• Initial exposure, helper T cells bind to exposed
  antigens on immune cells.
• Cytokines stimulate the production of B cells
  specific for IgE antibodies.
• Second exposure, those antibodies bound to mast
  cells bind to the allergic antigens which cause
  the mast cells to release histamines and start an
  allergic response.

IgE Mediated Hypersensitivity
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Antibodies label antigens for disposal by

• 1) Neutralization blocking the ability of a
  virus or bacterium to infect a host cell by
  binding to its surface

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2) Opsonization antibodies (opsonins) coat
microbes for phagocytosis by macrophages
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opsonization
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3) Antigen-antibody complexes on microbes can
activate the complement system and trigger a
membrane attack complex (MAC).
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Ys and Cs having a party!
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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
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Active and Passive immunity

• Active production of antibodies from exposure
  or from immunization
• Passive temporary immunity by antibodies
  supplied from the placenta, mothers milk, or
  antibody injection

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Immune Rejection

• Blood Matching Antibodies to blood group
  antigens can stimulate an immune response.
• A person will make antibodies to other blood
  antigens than its own.

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You make antibodies against any blood antigens
you do not have.
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• Transplanted tissue and organs are rejected due
  to foreign MHC molecules. The use of closely
  related donors and immune suppression drugs help
  to minimize rejection.

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• In bone marrow transplants, the recipients bone
  marrow cells are destroyed by radiation,
  eliminating the recipients immune system.
• The lymphocytes in the bone marrow transplant may
  produce a graft versus host reaction to the host
  cells if the MHC
• molecules are not
• closely matched.

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Immune System Disorders

• Allergies are hypersensitivities to certain
  environmental antigens, or allergens.
• - IgE antibodies produced in an initial
  exposure may bind to mast cells and cause a
  histamine response.

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• Anaphylactic shock is a severe allergic response
  in which vasodilation leads to a life-threatening
  drop in blood pressure

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• Autoimmune disease immune system turns against
  itself
• Ex - lupus, rheumatoid arthritis,
  insulin-dependent diabetes mellitus, and multiple
  sclerosis.

rheumatoid arthritis
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Lupus
Systemic lupus erythematosus (SLE) is a long-term
autoimmune disorder that may affect the skin,
joints, kidneys, brain, and other organs.
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Multiple Sclerosis

• Multiple sclerosis (or MS) is a chronic, often
  disabling disease that attacks the central
  nervous system (CNS).
• Symptoms may be mild, such as numbness in the
  limbs, or severe, such as paralysis or loss of
  vision.

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• The bodys own defense system attacks myelin, the
  fatty substance that surrounds and protects the
  nerve fibers in the central nervous system. The
  nerve fibers themselves can also be damaged.

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• Immunodeficiency may be developmental (genetic)
  or in response to a chemical, drugs, cancer,
  viruses (HIV).
• Severe combined immunodeficiency (SCID), is a
  genetic disorder in which both B cells and T
  cells) of the adaptive immune system are impaired
  due to a defect in one of several possible genes.
  

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• Exercising to exhaustion and stress can impair
  the immune system.

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Enzyme-Linked ImmunoSorbent Assay (ELISA)
used to detect antibodies
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Generalized ELISA protocol for detecting a target
antigen. Enzyme (E) is conjugated to secondary
antibody.
Bind sample(antigen) to support
Add primary antibody wash

Add secondary antibody-enzyme conjugate wash
Add substrate. If enzyme is present, then a
color change (blue) will occur.
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The need for controls

• Positive primary antibodies
• - to make sure assay is working
• Negative buffer
• - to make sure all samples are not positive
  and thus get a false positive

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HINTS!

• Label correctly!
• Do not contaminate!
• You can use 40 uL instead of 50 uL with the
  micropipettes. Amounts are not critical. This
  is a qualitative test!
• If you mess up, you will have to repeat the test
  AFTER SCHOOL!

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If serial dilutions are used, you can see
different intensities of antibodies present.
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Cell signaling and immunology

• In cells of the immune system, signaling leads to
  activation of cell-type specific immune
  activities.
• Ligand interaction with receptors on the surface
  of cells of the immune system triggers
  intracellular signal transduction directly or
  through association with assistant signal
  transduction molecules.

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Immune signaling serves a variety of functions

• apoptotic deletion of cells bearing receptors
  against self-peptides
• activation of immune and inflammatory response
  activities

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Signaling in the innate response

• Toll-like receptors (TLRs) appear to be one of
  the most ancient, conserved components of the
  immune system, and are the basic signaling
  receptors of the innate immune system.
• TLRs trigger signals evoking synthesis and
  secretion of cytokines and activation of host
  defenses through various pathways.

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Cytokines cell to cell

• secreted by immune cells in response to cellular
  signaling, and bind to specific membrane
  receptors, which then signal the cell via second
  messengers, often tyrosine kinases, to alter
  cellular activity (gene expression).
• Interleukins comprise the largest class of
  cytokines, and are manufactured by one leukocyte
  to act on other leukocytes as signaling ligands.
  Cytokines are often produced in cascades.

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Cytokine Signaling
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Signaling in the adaptive immune response

• Ligands
• Antigens
• MHC processed peptide pieces
• Hematopoietic growth factors (cause blood cells
  to grow and mature)

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• Signal Transduction
• Tyrosine-kinases
• 2nd messengers Ca ions, IP3,
• G-proteins, etc.
• Activation of transcription factors
• Response
• Transcribe mRNA into proteins for immune
  activation

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