Download Immunology: Specific Immunity

Immunology: Specific Immunity
• Immunity: not being susceptible to disease
• Types of immunity
– Innate: you have it from birth.
• Species: as humans, immune to diseases of
many other creatures
• Genetic: presence/absence of receptors
• Non-specific host defenses: Macrophages, etc.
– Acquired: after exposure, your body remembers
specific invader.
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Other views of immunity
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• 2 x 2 matrix: Immunity is either active or
passive; either natural or artificial.
• Active means that host is making his own
antibodies; passive means the antibodies came
from someone else.
• Natural means the antibodies
Active
Active
were acquired by the host thru
Artificial natural
natural means; artificial means
Passive Passive
they were injected.
Artificial natural
Nature of antigens
• The immune system recognizes, responds to,
and remembers molecules that are antigens.
• An antigen:
– Is foreign
– Is large
– Is molecularly complex.
• A molecule that is too small to be an antigen
without piggy-backing onto another is a hapten
• The specific part of an antigen recognized by
an antibody or receptor is called an epitope.
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Dual Nature of the immune system
• Humoral and cell mediated
– Humoral refers to body fluids, specifically that this
branch of the immune system uses antibodies
which are protein molecules dissolved in blood,
body fluids, and secretions.
• B lymphocytes are the source of antibodies
– Cell mediated refers to the direct involvement of
cells to attack an infection
• T lymphocytes either kill cells directly or recruit
macrophages to kill cells directly
Basics of antibodies
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• Protein molecules produced by activated B
cells.
• Belong to class of proteins called
immunoglobulins (Ig), subclass of globulins.
• Y-shaped molecule with hinges
– Ends include variable regions where antigen
binding occurs.
– Antibodies made by a single B cell are all the same,
differ from those made by another in variable
region.
Basic Antibody structure
•Molecule
undergoes
shape change
upon binding
to antigen.
•Classic lock
& key like an
enzyme.
Fc end: binds to host cells.
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The Antibodies
• IgG: most abundant in
blood and body fluids;
single Y shaped
molecule, remains in
circulation for long time.
• IgM: 5 Y-shaped units
linked together, first type
of antibody made in an
immune response.
http://www.neuro.wustl.edu/neuromuscular/pics/igm.gif
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The Antibodies
• IgA: present in large quantities in body secretions; a
dimer (2 Y-shaped units, tail to tail), helps protect
mucous membranes.
• IgE: single Y shaped unit, in small quantities, found
bound to mast cells attached by Fc end, involved in
allergies (mast cells release histamine).
• IgD: The receptor for antigen normally found on the
surface of B cells; if it is shed into bloodstream, looks
a lot like an IgG antibody. In very small amounts.
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Memory and antibody titer
Upon first
exposure to
antigen,
accumulation
of antibody is
slow.
Memory cells
make for a
quicker,
larger
response
afterwards.
This is the basis for booster shots.
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The Immune response
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• An immune response is what the immune
system does when confronted by an antigen.
• An immune response is an elaborate interplay
between antigen, non-specific defenses, and B
and T lymphocytes.
• The process involves direct contact (cells,
molecules bind to receptors on cell surfaces)
and cytokines (messenger molecules) that also
bind to receptors on cell surfaces.
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Take Immunology to learn the details of
how an immune response happens
Now for more on antibodies,
vaccines, and hypersensitivities.
How DO antibodies help?
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• Antibodies attach to antigens. Period. But…
– Because there are at least 2 binding sites, crossbridges form, linking antigens together in clumps.
– Attaching covers up critical sites on the antigens.
• Agglutination: Aby links cells, viruses together
to make clumps that attract macrophages.
• Precipitation: toxin molecules come out of
solution, can be cleared out.
• Neutralization: toxins, viruses no longer active.
How DO antibodies help?-2
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• Opsonization: an opsonin is something that
promotes phagocytosis.
– By making antigens into clumps.
– By providing a “handle” (Fc end of antibody).
• Complement fixation
– Antibody binds to antigen, antibody changes shape
– Shape change activates complement
• Activated complement leads to increased
inflammation, opsonization, and cell lysis.
Vaccines
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• From “vaccus”, Latin for cow, from Ed Jenner
using cowpox to immunize.
• Live attenuated vaccine
– Pathogen grown to make it weak, used alive.
• Killed/inactivated vaccine
– Destroyed with formalin, weaker immune response
• Subunit/conjugate/engineered
– A portion of pathogen used, often combined with
another molecule for effectiveness; antigen may be
produced through genetic engineering.
Hypersensitivities-1
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• Inappropriate immune responses
• Type II are cytotoxic reactions like the Rh factor
problem and bad blood transfusions.
– Rh is one of many blood groups, like ABO
– An Rh+ fetus in an Rh- mother means she gets
immunized by baby’s blood cells, makes Aby.
– Second pregnancy, fetal RBCs are attacked.
– Solution: give Rho-gam during 1st pregnancy.
• Type III are immune complex disorders, where
too many agn-aby clumps cause inflammation.
Hypersensitivities-2
Allergies
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• Type I are immediate type, in which antigen
binds to IgE on mast cells, histamine released.
– Histamine: smooth muscle contraction, vasodilation.
– Results in asthma, diarrhea, shock depending on
where antigen enters body. Ex. Bee sting.
• Type IV are delayed type, T cell produces
various cytokines which affect macrophages.
– The bar fight scenario: come, stay, get angry.
– Angry macrophages cause much tissue damage.
– Ex. Poison ivy; urushiol-coated cells killed.