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Innate immunity: The first line of defense How does your

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Title: Innate immunity: The first line of defense How does your


1
Innate immunity
  • The first line of defense

2
How does your body know whats dangerous?
  • Your body is constantly exposed to foreign
    agents
  • on the surface of your skin
  • when you breathe
  • when you eat
  • your body comes into contact with many things
    that are not made of the same materials as you
  • Sometimes you come into contact with things that
    are dangerous, like influenza virus, or the
    salmonella bacteria
  • A functioning immune system is able to sort out
    what is safe and what is dangerous

3
Self vs non self
  • Your bodys innate immune system is able to
    detect things that are dangerous
  • Things your immune system sees
  • Things that are normal and part of your body
    self (ex your DNA, your proteins)
  • Things that are not part of your body non-self
  • Not dangerous (ex a carrot that you eat, grass
    on your skin, perfume that you breathe in)
  • Dangerous (ex components of bacteria, viruses,
    parasites and fungi)

4
The innate immune system
  • This is the first line of defense in your immune
    system
  • The innate immune system is a little bit like a
    look-out system, it is only alerted when
    something different and dangerous comes along
  • The goal of the innate immune system is to detect
    pathogens and trigger an immune response

5
Analogy
  • The innate immune system is like a traffic cop
    parked on the street waiting to catch people
    speeding. The police officer has a detector that
    can calculate the speed of passing vehicles.
    When someone speeding passes by that, the
    detector measures it, and the cop issues a ticket
    to the speeder.
  • Cars passing by at legal speeds are normal, so
    the police officer doesnt stop them
  • these cars are normal, they are like the normal
    DNA and proteins in your body
  • The police officer needs a detector to be able to
    determine who is speeding
  • your innate immune system has pattern recognition
    receptors that determine whats dangerous and
    whats not)
  • Cars that are speeding are different and
    potentially dangerous, so the cop stops them.
  • When the cop stops the car, a series of steps are
    taken
  • a ticket is issued
  • the drivers information is registered in a
    database so that there is a record of the
    speeding.
  • When pattern recognition receptors detect
    something dangerous, and a series of steps occurs
    inside your cells to try to stop the dangerous
    agent from spreading and to warn your body

6
Info about innate immune system
  • If you did not have an innate immune system, your
    body would have no way to detect an infection!
  • The goal of the innate immune system is to detect
    pathogens and alert the adaptive immune system.
  • Characteristics of the adaptive immune system
  • adapts to generate specific immunity, get rid of
    the pathogen and remember what that pathogen
    looks like if it ever sees it again in the
    future.
  • Characteristics of the innate immune system
  • You are born with an innate immune system and it
    does not change or adapt as you encounter
    pathogens.
  • The innate immune system has no memory.
  • It is not specific to individual pathogens (ex
    does not specifically recognize the specific cold
    virus you had last winter, but it can recognize
    viruses in general)
  • The innate immune system can recognize patterns
    that are the same in many kinds of microbes.

7
Detecting patterns
  • All the cells in your body have Pattern
    Recognition Receptors (PRRs)
  • These PRRs are responsible for detecting
    dangerous foreign agents. How?
  • Different classes of microbes share certain
    characteristics that do not exist in human cells
    these are Pathogen Associated Molecular Patterns
    (PAMPs)
  • Example human cells have nucleic acids that are
    normal (DNA, mRNA, tRNA). Bacteria and viruses
    often have different nucleic acids.

8
The pattern recognition receptors in your cells
can tell which nucleic acids are dangerous and
which are normal.
9
There are PRRs in your cell membranes and inside
the cytoplasm of your cells. Scientists have
identified around 15 different PRRs in humans,
each of which is specific for a different
pathogen associated molecular pattern. That way,
viruses, bacteria, parasites and fungi can be
detected by the innate immune system.
10
  • When a microbe infects a cell, the PRRs can
    detect a PAMP from that microbe
  • This recognition activates a cascade of events
    involving cellular proteins.
  • At the end of this cascade, a protein is sent to
    the nucleus which signals the DNA to make
    proteins that start an immune response
  • These proteins can
  • Create an anti-infection state in the infected
    cell so as to slow the grow of the microbe
  • Warn surrounding cells that there is an invader
    nearby
  • Recruit cells from the immune system to come help
    clear the infection
  • Help activate immune cells that are specific for
    that particular microbe

Click once for the animation
11
Where is the innate immune system?
  • All your cells have PRRs, because all your cells
    are susceptible to infection!
  • Some cells have more types of PRRs and can
    respond quicker (ex dendritic cells)

12
  • When a virus infects a cell, a PRR detects it,
    triggering a cascade of signals.
  • Immune proteins are made
  • Some of these proteins are secreted and can warn
    surrounding cells that theres an infection
    nearby. Some proteins can recruit other immune
    cells to the site of infection.
  • The infected cell can break down viral proteins
    and show them to the newly recruited immune cell
    (a T cell)
  • The T cell is now activated and can recognize the
    specific piece of protein from that specific
    virus. Because of the signals from the innate
    immune response, the adaptive immune system can
    now generate a specific response against the
    virus, can clear the virus and remember that
    specific virus so it cant infect you again in
    the future.

Click once for the animation
13
You need both!
  • In order for the human immune system to work you
    need
  • An innate immune system
  • An adaptive immune system
  • Without either of these, your immune system would
    not work

14
Other species
  • Most multicellular organisms have an innate
    immune system
  • Other mammals have both innate and adaptive
    immune systems
  • Butinsects and plants only have an innate immune
    system!
  • Did you know
  • Pattern recognition receptors were first
    discovered in fruit flies
  • Sea urchins have over 200 different types of PRRs
    to defend themselves

http//www.news.wisc.edu/newsphotos/images/fruit_f
ly_research03_6801.JPG,
http//www.alaskaunderseatours.com/photos/Red-Sea-
Urchin.jpg
15
Conclusions
  • The innate immune system is the first line of
    defense against pathogens
  • Your cells have Pattern Recognition Receptors
    that can detect elements that are conserved in
    many kinds of microbes Pathogen Associated
    Molecular Patterns
  • Recognition of something dangerous leads to a
    signal that warns other cells and the immune
    system that there is an invader
  • Without the innate immune system, your body could
    not fight off infection!

16
Extra information
  • Pathogens are often able to trick the innate
    immune response

17
  • Many microbes are able to block the innate immune
    response.
  • Some are able to block this cascade of events at
    various stages
  • Examples
  • Influenza virus has a protein that is able to
    hide its RNA so that PRRs cant detect it.
  • Hepatitis C virus is able to break apart a
    protein involved in the innate immune cascade
  • Mycobacterium tuberculosis can prevent gene
    transcription

18
If a microbe blocks the innate immune response,
what happens?
  • Case 1 Immune system wins.
  • Microbes arent usually able to fully block the
    innate immune response. Therefore, a immune
    response is generated and the pathogen is
    cleared.
  • Ex Influenza virus. The virus cant block the
    whole innate immune response, and the infection
    is resolved.
  • Case 2 Pathogen wins.
  • In some chronic infections the immune system is
    never fully able to clear the pathogen.
  • Ex Hepatitis C virus. Microbes that cause
    chronic infections are able to block the innate
    immune response at many stages, and have methods
    to deter the adaptive immune response as well.
    Hepatitis C is a lifelong illness with no cure.
    The current treatment involves stimulating the
    innate immune system.

19
Made possible by
www.immunologymontreal.ca
www.cihr-irsc.gc.ca/synapse
www.mcgill.ca/hostres/training
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