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Specific Host Defenses: The
Immune Response
SECOND
LINE
A. Cells
1. Phagocytic Cells (neutrophils
and macrophages)
2. Natural Killer Cells
a. recognize body cells infected
with foreign bodies (i.e. viruses)
b. utilize perforins  "holeforming" proteins
Credit: © Dr. Richard Kessel & Dr. Gene Shih/Visuals Unlimited
This phagocyte or macrophage is able to ingest small particles that might be inhaled into the
lungs. SEM X1630.
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Credit: © Science VU/W.J. Johnson/Visuals Unlimited
A macrophage shown engulfing cancer cells. Macrophage cells circulate through the blood
stream searching for bacteria, dead or abnormal cells, or foreign objects to engulf. SEM
X3000.
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 B. Antimicrobial
Proteins
Cytokines- reg. intensity/duration
of immune response
 Interferons - produced by viral
infected cells, inhibits viral
replication
 Interleukins - secreted by
macrophages, lymphocytes; resets
thermostat
Chemokines
-attract and
direct movement of immune
sys. Cells
Tumor Necrosis Factors attacks tumors
Inflammatory Response –
 1. HISTAMINE release….
-histamine makes capillary walls
leaky, relaxes smooth muscle  blood
flows into wounded area: inflammation
…increased delivery of WBCs, etc.
 2. Clotting response - chemically
stimulated by wounded cells (platelets,
etc.)
3. Attraction of Phagocytic WBCs
(i.e. Macrophage) / pus
 C.
4.
Fever
elevated temperature...
- inhibits bacteria metabolism
- stimulates phagocytic WBCs
- increases production of interferon
in viral attacks
aspirin reduces fever; prolongs
viral (flu) infections
Complement
system
 group of proteins that aid in
immune response
functions include a) lysis b)
coating pathogens to make them
easier to catch c) attract white
blood cells – “chemotaxis” d)
stimulate immune response
Innate or Genetic Immunity:
Genetically determined.
May be due to lack of receptors
or other molecules required for
infection.
Immunity of mice to poliovirus.
Acquired Immunity:Immunity that
an organism develops during
lifetime.
ACQUIRED – ADAPTIVE
IMMUNITY
- ANTIGEN
PRESENTATION IS A
KEY CONCEPT!!!!
- APC (ANTI-PRESCELLS)
T Cells and Cell Mediated
Immunity
Cellular Components of Immunity:
T cells are key cellular
component of immunity.
T cells have an antigen receptor
that recognizes and reacts to a
specific antigen (T cell receptor).
T
cell receptor only recognize
antigens combined with major
histocompatability (MHC) proteins
on the surface of cells.
MHC Class I: Found on all cells.
MHC Class II: Found on
phagocytes.
Clonal selection increases number
of T cells.
T Cells Only Recognize Antigen Associated
with MHC Molecules on Cell Surfaces
T Cells and Cell Mediated
Immunity
1. T Helper (TH) Cells: Central
role in immune response.
+
Most are CD4
Recognize antigen on the
surface of antigen presenting
cells (e.g.: macrophage).
Activate
macrophages
Induce formation of
cytotoxic T cells
Stimulate B cells to
produce antibodies.
Types of T cells (Continued)
2. Cytotoxic T (Tc) Cells:
Destroy target cells.
Recognize antigens on the
surface of all cells:
•Kill host cells that are
infected with viruses or
bacteria.
•Recognize and kill cancer
cells, transplanted tissue.
Release protein called
perforin which causing lysis
of infected cells.
Undergo apoptosis when
stimulating antigen is gone.
Credit: © Dr. Dennis Kunkel/Visuals Unlimited
Human T-lymphocyte attacking fibroblast tumor/cancer cells. SEM X500.
284555
Credit: © Science VU/Visuals Unlimited
Cancer cell with several T-lymphocytes attacking it.
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Credit: © Science VU/Visuals Unlimited
Two dead cancer cells, their cell walls and bodies disintegrating after a successful Tlymphocyte attack.
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Types of T cells (Continued)
3. Delayed Hypersensitivity T
(TD) Cells: Mostly T helper
and a few cytotoxic T cells that
are involved in some allergic
reactions (poison ivy) and
rejection of transplanted tissue.
4. T Suppressor (Ts) Cells: May
shut down immune response.
Immune
system is an example of
positive feedback
system enhances a runaway effect
TH activation by MHC II releases
interleukins which stimulates B
cells and other T cells
interleukins stimulates activity of
TH cells
TH
cell stimulates B cells specific
for antigen to become plasma
cells.
Antigens are mainly proteins on
viruses, bacteria, foreign red
blood cells…
Duality of Immune System
I. Humoral (Antibody-Mediated)
Immunity
Involves production of
antibodies against foreign
antigens.
Antibodies are prod. by type
of lymphocytes called B cells.
B
cells stim. will secrete
antibodies called plasma cells.
Antibodies are found in ECF
(blood plasma, lymph, mucus,
etc.) and the surface of B cells.
Defense against pathogen/toxins
before they enter cells.
Also cause certain reactions
against transplanted tissue.
Antibodies
Proteins that recognize and bind to
a particular antigen with very high
specificity.
Made in resp. to exp. to antigen.
One virus or microbe may have
several antigenic determinant sites,
to which different antibodies may
bind.
GENERATING ANTIBODY
DIVERSITY – 3 mechanisms
1) Genomic Rearrangement (during
differentiation)
2) Insertions/Deletions when
“pasted” together
3) Hypermutation – up to 10,000
times higher than normal
STEM CELL DNA FOR ANTIBODY
PRODUCTION
How Do B Cells Prod. Antibodies?
Clonal
Selection: When a B cell
encounters an antigen it recognizes,
it is stimulated and divides into
many clones called plasma cells,
which actively secrete antibodies.
Each
B cell produces antibodies
that will recognize only one
antigenic determinant.
Humoral Immunity (Continued)
Apoptosis
Programmed cell death (“Falling
away”).
Human body makes 100 million
lymphocytes every day. If an
equivalent number doesn’t die,
will develop leukemia.
Duality of Immune System….
II. Cell Mediated Immunity
specialized set of lymphocytes
called T cells that recognize
foreign antigens on the surface
of cells, organisms, or tissues:
Helper
T cells
Cytotoxic
T cells
T
cells regulate proliferation and
activity of other cells of the
immune system: B cells,
macrophages, neutrophils, etc.
Clonal
Deletion: B and T
cells that react against self
antigens appear to be
destroyed during fetal
development. Process is
poorly understood.
Immunological Memory
Primary Response:
After initial exposure to
antigen, no antibodies are
found for several days.
Most B cells become plasma
cells, some memory cells.
Gradual decline of antibodies
Secondary Response:
Subsequent
exposure to the same
antigen displays a faster and more
intense antibody response.
Increased antibody response is
due to the existence of memory
cells, which rapidly produce
plasma cells upon antigen
stimulation.

AUTOIMMUNITY
 Lupus
- immune response to your
own cells parts (especially nucleic
acids)
 rheumatoid arthritis - immune
response to joint cartilage
 insulin-dependant diabetes –
attacks beta cells of pancreas
 multiple sclerosis - attack myelin
sheath

Allergic Response -over-reaction
to a harmless substance

response is caused by histamine
• tissue swelling , excess
mucous (yum)
• constricted airway poss.
Anaphylatic shock
• sneezing
• tears
Rh
Blood Group and Pregnancy
Rh – mother can produce
antibodies to Rh + child
Immune system can attack Rh+
child (2nd pregnancy)
Potential PATHOGENS
- bacteria, viruses, parasites
Prions can cause Bovine Spongiform
Encephalopathy: “Mad Cow
Disease”  cause by a protein!
KURU
 AIDS
 HIV
attacks TH cells
 some cells are killed by
immune system but others
produce more virus
 immune system slowly
loses
Credit: © Dr. Hans Gelderblom/Visuals Unlimited
HIV (Human Immunodeficiency Virus) budding. HIV infects a number of cells in the body,
though the main target is a lymphocyte cell, which is a type of T-cell. Once the HIV virus has
infected the host cell it then replicates itself with thousands of copies. TEM X120,000.
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