The Immune system
The Immune system is the body’s
defense system
• Against:
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Bacteria
Viruses
Protists
Other living invaders
Toxins
Foreign debris
Cancerous cells
• The immune system is
complex
• Defends against threats
known and unknown
Elements of the Immune system
• Many lines of defense, for
many kinds of threats
• Skin
• Blood
• Thymus
• Spleen
• Lymphatic system
• Mucous membranes
• Bone marrow
Innate vs. Adaptive immunity
Innate Immunity
• Non-specific
• Defends against known
invaders
• Skin, lysozyme
• Pre-existing
• Cannot adapt to changing
threats
Adaptive Immunity
• Mechanisms which fight
specific invaders
• For unknown threats
• Responsive
• Requires time to build
defense (days)
• Cannot anticipate threats
• Remembers previous
threats
Humoral vs. Cell-mediated Immunity
Cell- Mediated Immunity
• Live cells kill invaders
• Innate: Phagocytic cells
(e.g. macrophages,
neutrophils)
• Adaptive: B lymphocytes
and T lymphocytes create
specific responses to unique
invaders
Humoral immunity
• Proteins in blood
(“humors”)
• Innate- complement
system, clotting factors,
cytokines, etc.
• Adaptive: Antibodies
Blood is a mixture of cells and plasma
Human Blood after centrifugation
• ~55% Plasma
• ~45% Red blood cells
• <1% White blood cells and
platelets (“buffy coat”)
Blood plasma
• Water
• Nutrients
• Solutes- Na+, Cl-,
wastes, CO2, etc.
• Contains humoral
immune elements
• Some innate immunity
All blood cells are part of the
hematopoetic stem cell lineage
Hematopoetic stem cells differentiate
into all blood cells
• Pluripotent- able to
become any one of
many cell types
• Includes T cells, B
cells, macrophages,
etc.
Red blood cells carry oxygen and CO2
• Lose nucleus in
development
• Short-lived, no repair
• Packed solid with
hemoglobin
• Membranes designed to
maximize surface area
• Facilitate gas transfer
Hemoglobin
• The oxygen-carrying
protein
• Heterotetrameric protein
• 2 alpha subunits, 2 beta
• Each subunit holds a
Heme group
• Each heme holds an Fe++
ion
• Each Fe++ can bind an
O2
Hemoglobin binding curve
• In areas of High O2
(e.g., lungs)- binds O2
very well (picks up O2)
• In areas of Low O2 (e.g.,
muscles) binds O2
poorly (drops off O2)
• Myoglobin binds O2 in
muscle & organ tissues
Platelets assist with blood clotting
• Recruit plasma protein
fibrinogen to a cut
• They release clotting
factors
• Clotting factors convert
fibrinogen to fibrin
• Fibrin net prevents
blood loss
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The liquid part of blood is called
A) water.
B) plasma.
C) serum.
D) extrastitial fluid.
E) anionic fluid.
White blood cells come in a great
variety of types
Elements of Innate Immunity
Lysozyme- an innate enzymatic
defense
• Enzyme that cuts
bacterial cell walls
• Also cuts chitin, a
constituent of fungal
cell walls and arthropod
exoskeleton
• Found in mucous, tears,
egg whites
Complement- humoral defense against
non-specific invaders
• A biochemical cascade
• Non-specific
• Signalling pathway to
cause cell lysis
• Also Recruitable by
adaptive immune
system
Interferons are nonspecific anti-viral
signalling molecules
Phagocytic white blood cells devour
bacteria
• Which of the following, produced by virusinfected cells, diffuses to neighboring cells to
help them fight a viral infection?
• A) lysozyme
• B) interferon
• C) histamine
• D) antigen
• E) interleukin-2
The Inflammatory response
Keeping the body safe comes at a cost
• Inflammation
implicated in heart
disease, etc.
• Gum inflammation
linked to heart attacks
The lymphatic system collects lymph
and houses white blood cells in nodes
Adaptive Immunity contains humoral
and cell-mediated components
Adaptive Immunity is learned, and has
memory
Antibodies- the Key component of
humoral adaptive immunity
• Two light chains, two
heavy chains
• Each contains a variable
region and a constant
region
Antigen- anything which can be bound
by an antibody
B Cells- the
source of
antibodies
Clonal
selection
musters
B-cell
defense
forces
against
specific
antigens
Adaptive Immunity is learned, and has
memory
Immune cells are the only cells with
different DNA
• VDJ recombination of light
and heavy chains generate
antibody diversity
• Change is permanent
• A form of Russian Roulette
for the cell
• Successful recombination
creates a binding antibodycell survives
• Unsuccessful- cell is
destroyed
• Finding a good cell takes time
Bound antibodies are the mark of
death for invaders
Breast milk contains maternal
antibodies
• Infants have no
acquired immunity
• Mother’s acquired
immunity is transferred
to the baby through
nursing
• Passive immunity
• Is not retained by the
baby
Vaccination gives the body active
immunity
• An antigen sample is
given to a person
• Person’s immune system
mounts a response to the
antigen
• Antigen can be
deactivated/destroyed
virus particles, etc.
• No waiting time for body
to develop 2o immune
response
Antibodies can be used as therapy
• Some growth factors
are overactive in certain
cancers
• Antibody binds to
growth factors, or their
receptors
Polyclonal Antibodies
• From multiple B cells
• Bind to different
epitopes of an antigen
Monoclonal antibodies
• Obtained from a
single B cell
• Bind to a single
epitope
• A single B cell is
fused to a myeloma
cell
• Myeloma cells are
immortal
Mouse antibodies can be humanized
• Constant regions of
mouse antibody are
gradually replaced with
human sequences
Fluorescent antibodies can be used in
scientific experiments
• Fluorescent molecules
can be linked to
antibodies
• Antibodies show us
where proteins exist in
vivo
In an ELISA, Horseradish Peroxidase is
linked to a 2o antibody
Indirect ELISA
To detect the presence of an antibody
Primary Antibody
Secondary Antibody
Wash
Block
Wash
Substrate
Home pregnancy tests utilize
antibodies
• The transfer of antibodies from breast milk to
an infant is an example of __________
immunity.
• A) nonspecific
• B) passive
• C) humoral
• D) active
• E) cell-mediated
T cells are the primary cell-mediated
adaptive immune response
Major Histocompatibility Complex
(MHC or HLA)
• MHCI
Found on all cells, recognized by TC cells
• MHCII
Found on B cells and Macrophages
recognized by TH cells
When presented with antigen, Helper T
cells recruit other immune cells
• The basic function of T cells is to identify and
destroy invaders in our
• A) blood or lymph.
• B) interstitial fluid.
• C) cells.
• D) immune system.
• E) brain.
CD4 on the surface of TH cells is the
site of HIV binding
Any known stage of the HIV life cycle is
a potential point for therapy
Protease inhibitors prevent formation
of HIV capsids
AZT is a nucleoside analog reverse
transcriptase inhibitor
AZT
Thymine
Cytotoxic T cells destroy infected body
cells
In Autoimmune disease, the immune
system attacks the self
Allergies are immune responses to
harmless antigens
• A substance that can elicit an immune
response is called a(n)
• A) complement.
• B) interferon.
• C) histamine.
• D) antibody.
• E) antigen.
• Which one of the following statements about HIV
is false?
• A) The genome of HIV consists of RNA.
• B) HIV attacks helper T cells.
• C) New HIV are produced inside helper T cells.
• D) HIV is transmitted by body fluids transporting
infected cells.
• E) Some antibiotics have proven effective in
combating the spread of AIDS.
• Which type of immune response is always
disadvantageous to a person?
• A) cell-mediated
• B) inflammatory
• C) humoral-mediated
• D) autoimmune
• E) All immune responses are advantageous.