Download Evolution of the Immune System

Immune System Part I:
The Evolution of the Immune System
Immune System and Innate Immunity
• The human body has over 100 trillion
bacteria living on it or within it.
• An immune system protects an organism
from pathogens and other foreign material.
• The innate immune system provides the
first line of defense by
• activating a small variety of immune
cells to produce molecules that stop the
invading pathogens and its resulting
disease
• providing physical barriers to stop a
pathogen
Adaptive Immune System
• The innate immune system is immediate
and utilized by many multicellular
organisms.
• In contrast, an adaptive immune
system produces antibodies specific to a
pathogen or foreign particle after the
pathogen activates B- and Tlymphocytes.
• The adaptive immune response is slower
than the innate immune response and it
may take days to become effective.
• Present only in jawed vertebrates
Homeostasis and the Immune System
• Pathogens invade organisms
because they are seeking:
- a source of food or water
- protection
- a place for reproduction
• Defense mechanisms evolved
to rid the organism of
pathogens and return the
organism back to its original
state.
Evolution of the Immune System
• Ancestral amoebas performed
phagocytosis to obtain food.
• It would be advantageous for
these ancestral amoeba to be
able to distinguish between
self and non-self when
ingesting other cells.
• The interaction between
receptors and signature
molecules could provide this
distinction mechanism.
General Cell Communication
(Remember this stuff?!?)
Propose a cell communication mechanism that
ancestral amoeba may have used to distinguish
between foreign cells and other amoeba cells …
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Cell Communication and Immune System
Example of receptors
and various signature
molecules or PAMPs.
•Explain how this part of
the immune system is an
example of cell
communication.
•List all the observations
you can make about this
diagram.
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Evolution and Immunity
Toll-like
receptor
(TLR)
pathways
comparison
for plants,
invertebrates
and
vertebrates
1. List any similarities that you observe among the 3
pathways.
2. If this pathway was once in an ancestral cell, explain
why the differences exist between the three organisms.
Plant Defenses
Plants, like animals,
must defend against
pathogens and
herbivores with:
• physical barriers
• secondary
metabolites
• immune
responses
Plants’ Physical Defenses
• Pathogens can invade plants.
• Plants’physical defenses include:
- hairs that insects cannot
penetrate
- thorns or spines that large
herbivores avoid
- waxy cuticles that bacteria and
fungi cannot penetrate
Plant Defenses Against Herbivory
•Herbivores harm plants by
eating them.
•Defenses against herbivory
include production of
secondary metabolites.
Defense and Secondary Metabolites
Plant Defenses Against Herbivory
Plant Defenses Against Herbivory
Coevolution of Herbivores and Plants
• Certain herbivores and plants have
coevolved with one another.
• This butterfly can breakdown the secondary
metabolite produced by the passion vine and use
a nitrogen by-product in protein metabolism.
Induced Defense Response
•Certain pathogens will produce
molecules that produce the
hypersensitive response (HR).
•This results in localized death of
plant cells very quickly.
Systemic Acquired Resistance
•
Methyl salicylate from
the HR is spread to rest
of the plant.
•
Once converted to
salicylic acid, a
transduction pathway is
activated causing
systemic acquired
resistance (SAR) for the
entire plant that lasts for
several days.
Immunity and Invertebrates
-- Physical Barriers -Examples of innate immunity in Drosophila:
•First line of defense is the exoskeleton made of chitin.
•Chitin also lines the digestive tract.
•The enzyme lysozyme found in the gut breaks down the
cell walls of bacteria.
Innate Immunity
• If the pathogen escapes
the digestive tract, it will
be in a fluid called
hemolymph.
• Moving throughout the
hemolymph are
hemocytes.
• Some hemocytes can
destroy pathogens by
phagocytosis.
Innate Immunity
• Some hemocytes have Toll receptors that
produce antimicrobial peptides which
inactivate or kill fungal or bacteria by
disrupting plasma membranes.
• Each Toll receptor identifies certain signature
molecules as a pathogen or foreign material.
Toll Receptor
•
The Toll receptor recognizes
signature molecules or
PAMPs.
•
This activates signal
transduction pathways, often
producing transcription
factors.
•
These transcription factors
activate genes needed to
synthesize anti-microbial
peptides for destruction or
deactivation of pathogens.
Evidence
These flies were engineered
so that the immune cells
expressed a green
fluorescent protein when the
innate immune system was
activated.
The top fly was inoculated with bacteria and the
one below was “stabbed” with a sterile needle (no
injection of bacteria). The top fly’s immune system
was activated while the bottom fly’s was not.