SOMETIMES THE INNATE IMMUNE RESPONSE IS NOT ENOUGH

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SOMETIMES THE INNATE IMMUNE RESPONSE IS NOT ENOUGH
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SOMETIMES THE INNATE IMMUNE RESPONSE IS NOT ENOUGH
Listeria monocytogenes proliferate inside
macrophages.
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TODAY
INTRODUCTION TO ADAPTIVE IMMUNITY Chapter 1.
Pages 4 - 20
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ADAPTIVE IMMUNITY IS A NEW KID ON THE BLOCK
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ADAPTIVE IMMUNITY
Adaptive immune responses are distinct from
innate immune responses
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ADAPTIVE IMMUNITY HAS SEVERAL PROPERTIES THAT
DISTINGUISH IT FROM INNATE IMMUNITY
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ADAPTIVE IMMUNE RESPONSES ARE GENERATED IN
RESPONSE TO ANTIGENS
ANTIGEN Originally meant Antibody Generation.
Now expanded to include any macromolecule that
activates B or T lymphocytes.
Antigens Proteins Lipopolysaccharides Lipid
s Nucleic acids
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ORIGIN OF LYMPHOCYTES
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Antigens are detected by specialized T cell
receptors (TCR) or B cell receptors (BCR).
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B cells recognize antigen structures in three
dimensions, while T cells are more two
dimensional or even linear.
Kuby 3-1
T cells B cells
B cells
B cells
B cells
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B and T cells mediate two distinct forms of
adaptive immunity
1. Humoral Immunity. Directed against
extracellular microbes. Mediated by B
lymphocytes. B lymphocytes secrete antibodies
that neutralize and eliminate microbes and
microbial toxins.
2. Cellular Immunity. Directed against
intracellular microbes. Mediated by T
lymphocytes. T lymphocytes activate phagocytes
and lymphocytes or kill infected host cells.
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HUMORAL AND CELLULAR IMMUNE RESPONSES ARE
DISTINCT ARMS OF THE ADAPTIVE IMMUNE SYSTEM
TAILORED TO REPLY TO DISTINCT MICROBES.
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PHASES OF THE IMMUNE RESPONSE
1. Recognition Naïve lymphocytes recognize
corresponding antigen.
2. Activation Lymphocytes differentiate and
start clonal expansion.
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CLONAL EXPANSION
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PHASES OF THE IMMUNE RESPONSE
3. Effector phase. Differentiated lymphocytes
initiate microbial elimination.
4. Decline After microbial elimination the
signal for lymphocyte activation disappears. Most
of the cells activated by antigen die by a
process of programmed cell death (apoptosis).
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Specificity in Adaptive Immunity
1. Prior exposure to one antigen results in
stronger responses to subsequent challenges with
the same antigen but not to challenges with
other, even similar antigens.
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Memory in Adaptive Immunity.
The immune system launches stronger and more
effective responses to the same antigen with
repeat exposures
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THE B LYMPHOCYTE FAMILY
Each B cell expresses a unique B cell receptor
(BCR), which recognizes a distinct microbial
3-dimensional structure.
One B cell produces a single kind of antibody
specificity.
In a B cell that has never previously encountered
its target structure (naïve B cell), the BCR is
restricted to the plasma membrane of the B cell.
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The B lymphocyte family.
Naïve B cells are activated by antigens and other
second signals.
Activation of B cells results in their
proliferation (clonal expansion) and
differentiation into effector cells that actively
secrete antibodies
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• ANTIBODY - The Business End of the Humoral Immune
  Response.

Source B lymphocytes (B cells).
Released into circulation and mucosal fluids by B
cells upon infection.
Neutralize microbes and microbial toxins present
in the blood and in the lumens of mucosal organs
(G.I. Tract and respiratory tract).
Stops microbes from gaining access to and
colonizing host cells.
Do NOT have access to intracellular microbes.
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THE T LYMPHOCYTE FAMILY
ANTIGEN PRESENTING CELLS (APC)
APC line the potential sites of entry for
microbes (skin, G.I. tract, respiratory tract,
etc.). APCs capture, process and present antigens
to T lymphocytes in peripheral lymphoid tissues .
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THE T LYMPHOCYTE FAMILY
T cells also express clonotypic antigen
receptors. A single T cell recognizes a single
T cell antigen.
Th CD4
Tc CD8
Unlike B cells, T cells have co-receptors that
aid antigen receptors in recognition.
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WE DISTINGUISH TWO CLASSES OF T LYMPHOCYTES
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The T lymphocyte family.
A killer T (Tc) cell killing an infected host
cell.
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Due to the degree of specificity the Immune
system is also presented with a dilemma. How do
you bring the right lymphocyte together with its
cognate antigen upon infection quickly enough to
activate the appropriate immune reply?
The Peripheral lymphoid organs (lymph nodes,
spleen, mucosal and cutaneous lymphoid tissues)
concentrate antigens and lymphocytes to optimize
interactions.
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THE LYMPHATIC SYSTEM
A network that transports fluids from tissues to
the circulatory system.
Unlike the circulatory system, the lymphatic
system is not closed and has no central pump.
Excess interstitial fluid is collected by the
lymphatic system and is processed by lymph nodes
prior to being returned to the circulatory system.
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LYMPH NODES
Fluid from epithelia, collective tissues and
parenchymal organs drains to the lymph nodes.
This means that lymph contains a collection of
materials from epithelia and tissues. As such, it
is an ideal sample of the likelihood of an
ongoing infection. APCs sample the fluid at these
sites or travel here presenting antigens found
in epithelial microbes. In this manner, antigens
from throughout the body become concentrated in
draining lymph nodes.
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SPLEEN
The spleen is an abdominal organ that
concentrates blood-borne antigens. Antigens are
transported to the spleen by dendritic cells and
macrophages. The spleen is rich in phagocytes
that ingest and destroy microbes in the blood.
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LYMPHOCYTES CONSTANTLY RECIRCULATE BETWEEN
TISSUES TO MEDIATE MICROBIAL KILLING
Lymphocyte recirculation is essential for T cells
to meet their targets.

• T cells mature in the Thymus.

2. T cells enter lymph nodes, where they
encounter APCs.
3. T cells are activated and differentiate in the
lymph nodes.
4. T cells exit lymph nodes and enter circulation
where they mediate microbial destruction.
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SUMMARY

• Adaptive Immunity has humoral (B lymphocytes) and
  cellular (T lymphocytes) components.

2. Lymphocytes are cells of the adaptive immune
response that express clonally distributed
antigen receptors.
3. B lymphocytes produce antibodies in response
to three dimensional shapes. T lymphocytes
recognize peptide fragments of protein antigens
on other cells.
4. APCs capture antigens and concentrate them in
lymph nodes.
5. Lymphocytes and APCs are organized in
peripheral lymphoid organs where immune responses
are initiated and develop.
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