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Current Topics
 Organ transplants - stem cells, xenografts
 Allergies - more common? More serious?
 Vaccinations - stricter requirements?
 Possible epidemics - avian flu, SARS
 HIV and AIDS
 Stress
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Defense Systems
 Pathogens
 Lymphatic system
 Nonspecific defenses
 First line
 Second line
 Specific defenses
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Pathogens: Bacteria
 single celled, prokaryotic
 antibiotics based on differences between
prokaryotic and eukaryotic cells
 Infections can result in toxins
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Viruses
 Extremely small
 “parasitic DNA” or RNA
 Enter cells via endocytosis
 Diseases: AIDS, hepatitis, encephalitis,
rabies, colds, warts, chicken pox
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Prions
 Infectious proteins
 Cause folding problems of normal brain
proteins
 Resist cooking, freezing, drying
 Diseases: bovine spongiform encephalitis
(BSE), Creutzfeld-Jakob disease (CJD)
 Other pathogens: protozoa, fungi, worms
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Determination of Health Risk
 Transmissibility: how easily passed from
person to person
 Mode of transmission: respiratory, fecal-oral,
body fluids
 Virulence: how much damage caused by
infection
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Lymphatic System
 Functions:
 Maintain blood volume in cardiovascular
system
 Transport of fats from digestive system
 Filters out foreign material to defend
against infection
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Lymphatic Characteristics
 Lymph – from excess tissue fluid
 lymphatic vessels
 One way system toward the
heart
 No pump; lymph moved by
- milking action of skeletal
muscle
- smooth muscle in vessel walls
- one-way valves
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Lymphatic Vessels
Lymph capillaries have flap-like minivalves
 Fluid leaks into lymph capillaries
 anchored by filaments
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Lymph Nodes
 Defense cells within lymph nodes
 Macrophages – engulf and destroy foreign
substances: bacteria, viruses, cancerous
cells, cell debris
 Lymphocytes – provide immune response
to antigens
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Lymphatic System: Components
 Lymph
 Lymph nodes
 Spleen: cleanses blood,
removes dying red blood
cells, helps fight infection
 Thymus: secretes
hormones that cause T
lymphocytes to mature
 Tonsils: protect throat
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Body Defenses
protects against variety of
invaders
Specific for each type
of invader
responds immediately
Figure 12.6
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Surface Membrane Barriers – First Line
of Defense
 Skin - physical and chemical defenses
 Keratin, dead cells
 Constant replacement; pathogens also shed
 pH 5-6 inhibits bacterial growth
 Antibiotic peptide in sweat
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Surface Membrane Barriers
 Saliva and lacrimal fluid contain lysozyme
 Mucus traps microorganisms in digestive and
respiratory pathways
 Stomach mucosa
 Secretes HCl acid
 Has proteases
 Vomiting, defecation, urination
 Resident bacteria
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Second Line of Defense: Defensive Cells
1. Phagocytes (neutrophils
and macrophages)

Engulf foreign material
into a vacuole
2. Eosinophils
3. Natural killer cells (NK)
 lyse and kill cancer
cells, virus-infected
cells
 Secrete perforins that
destroy membranes
Figure 12.7a
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Antimicrobial Chemicals
 Complement
 A group of at least
20 plasma proteins
 Activated when
they attach to cells
(complement
fixation)
 Damage foreign
cell surfaces
Figure 12.10
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Antimicrobial Chemicals
 Interferons
 proteins secreted by virus-infected cells
 bind to surfaces of nearby healthy cells to
inhibit virus entry, replication
 = alert system
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Inflammatory Response
 Triggered when tissues are injured
 Produces four cardinal signs
 Redness
 Heat
 Swelling
 Pain
 Prevents spread of damaging agents
 Disposes of cell debris and pathogens
 Sets the stage for repair
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Steps in the Inflammatory Response
Figure 12.8
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Fever
 Abnormally high body temperature
 Hypothalamus control reset by pyrogens
(secreted by WBCs)
 Fever inhibits release of iron and zinc from
liver and spleen (needed by bacteria)
 Fever speeds tissue repair
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Defense Mechanisms
fever
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Specific Defense: The Immune System
 Antigen-specific – acts against particular
foreign substances
 Systemic – not restricted to the initial
infection site
 Has memory – mounts a stronger attack on
“known” pathogens
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Antigens (Nonself)
 Any substance capable of activating the immune
system response
 Examples
 Foreign proteins, large carbohydrates
 Haptens - small molecules that bind to our
proteins and become antigenic
 Pollen grains, microorganisms
 MHC - Major Histocompatibility Complex
are cell surface proteins that provide unique
“fingerprint” on each person’s cells
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Cells of the Immune System
 Lymphocytes
 Originate from hemocytoblasts in red bone marrow
 B lymphocytes mature in bone marrow
 Antibody-mediated immunity (humoral) Cells produce chemical defense (antibodies)
 T lymphocytes mature in thymus gland
 Cellular immunity - living cells attack invader
 Mature = become immunocompetent, able to react
with antigen
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Cells of the Immune System
 Lymphocytes
 Macrophages
 Arise from monocytes
 reside in lymphoid organs
 Consume foreign particles
 Present antigens on their surface as a signal to
B, T cells
 Release chemicals (monokines) that stimulate
immune response
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Antibody-Mediated Immune Response
 B cell with specific
receptors binds to its
specific antigen
 binding activates the B cell
to divide rapidly,
producing a clone
 Plasma cells secrete
antibodies into lymph
 Memory cells of same
clone
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Secondary Response
 Memory cells are
long-lived
 2nd exposure
causes a rapid
response
 Secondary
response is
stronger and
longer lasting
Figure 12.13
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Antibodies (Immunoglobulins) (Ig)
 IgG shown here:
 Four amino acid
chains linked by
disulfide bonds
 2 heavy chains, 2
identical light chains
 Specific antigenbinding sites are
present
Figure 12.15b
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Antibody Function
 Antibodies inactivate antigens in a number of
ways
 Complement fixation
 Neutralization
 Agglutination QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
 Precipitation
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ANTIBODY FUNCTION ANIMATION
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Antibody Classes
 Antibodies of each class have slightly different roles
 Five major immunoglobulin classes
 IgM – can fix complement; ABO blood system
 IgA – found mainly in mucus, mother’s milk
 IgD – important in activation of B cell
 IgG – most common; can cross the placental
barrier and protect fetus
 IgE – least frequent; involved in allergies
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Monoclonal Antibodies
 Antibodies from descendents of a single cell
line
 Examples of uses
 Diagnosis of pregnancy
 Treatment after exposure to hepatitis and
rabies
 Targeted drug delivery
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Cellular (Cell-Mediated) Immune
Response
Figure 12.17
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Cell-Mediated Immune Response
T cells: 4 types
Helper T cells:
stimulate other immune
cells
Cytotoxic T cells: kill
abnormal and foreign
cells
Memory T cells:
reactivate on reexposure
Suppressor T cells
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Summary of the Immune Response
Figure 12.19
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Active Immunity
 B cells encounter
antigens and
produce antibodies
 Active immunity
can be naturally or
artificially acquired
 Passive immunity:
use of antibodies
made elsewhere
Figure 12.14
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Tissue Rejection
 Transplants: 75%+ match of MHC essential
 Autografts, isografts
 Allografts, xenografts
 improvements in immunosuppressive drugs,
better tissue typing, national organ banks
 New technologies:
 Stem cells - adult, cord blood,
embryogenic
 Engineered pigs
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Disorders of Immunity: Allergies
(Hypersensitivity)
 Abnormal, vigorous immune responses
 Triggered by IgE
 Localized: affects only the area exposed
 Systemic: affects several organ systems
 Anaphylactic shock – severe, systemic
inflammatory response
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Allergy Mechanisms
First exposure: antigen
invades body, IgE antibodies
produced and bind to mast
cells.
Second exposure: antigens bind to
IgE, cause release of histamine
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Autoimmune Diseases
 The immune system does not distinguish
between self and foreign molecules
 The body produces antibodies and sensitized
T lymphocytes that attack its own tissues
Multiple sclerosis
Myasthenia gravis
Juvenile diabetes
Rheumatoid arthritis
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Self Tolerance Breakdown - How?
1. Inefficient lymphocyte programming
2. Appearance of self-proteins in the
circulation that have not been exposed to
the immune system
3. Cross-reaction of antibodies produced
against foreign antigens with self-antigens
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AIDS Pandemic
 More than 36 million
infected with HIV
worldwide
 Increasing spread in
Asia and India
 Outside U.S., most
often spread by
heterosexual contact
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 HIV is a retrovirus
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Invasion of T cell by HIV
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Time Course of the Progression of AIDS
after HIV Infection
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Figure 9.21
 AIDS quilt
Figure 10.22x2
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Safer Sex
 Transmission: body fluids, i.e., blood, semen,
breast milk, vaginal secretions
 Abstinence
 Reduce number of sexual partners
 Choose sexual partners with low-risk
behavior
 Use latex or polyurethane condoms or
barriers
 GET TESTED
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