November 5th 2012
November-05-12
12:36 PM
Ecological Immunology
The basic principle of this is that disease kills (or reduces fitness at the very least)
So therefore there should be positive selection on mechanisms that can resist disease
o Despite this, no animal has ever evolved with perfect immunity?
o Why?
Red Queen Hypothesis
Pathogens evolve even more rapidly than you do
For example, if tape worms are able to reproduce every few weeks, think how
many generations they would go through in your 70+ year lifespan. Much more
chance to evolve more rapidly than you
Immune systems are not "free"
You must "pay" something to maintain them
o Immune system is damaging
o Energy you invest in your immune system cannot be used toward reproduction, so the more
you give to immunity, the more you have to take from somewhere else
Immune system costs
Energy (calories from food)
o
Some must be used to keep your immune system online
o Hard to measure energy consumed when not in use, but can and have measured it when in
use (using these methods)
Increased metabolic rate = increased demand for energy, increases during increased
immune response (As much as 15% increase in basal metabolic rate)
Increased consumption of glucose
Comes from a variety of stores, when really run down, it begins depleting fat
reserves
Resources
o Things required for immune system as well as other functions, so you only have so much,
and have to balance its use
o Immunity requires scarce resources, not only calories
Such as carotenoids
o
These resources put a limit on how much you can put into your immune response, if you are
short on these resources, the amount you can put into your immune system is limited
Immunopathology
o In immune response, we make these reactive molecules, like reactive oxygen species (ROS)
These are "thrown" at pathogens to help destroy them
But too much can do damage to yourself
Only a problem if your ROS molecules outweigh your antioxidants
Oxidative Stress
Reactive molecules
o
Damage cell membranes, DNA, leading to cellular dysfunction and/or death Such as hydroxyl radicals that steals H from a unsaturated fatty acid
Which leaves a reactive carbon radical
Which can then bind to things like oxygen
Known as Lipid peroxidation
Lipid Peroxidation
Can have numerous negative effects
This process is how pathogens are destroyed by ROS molecules, however are not very specific so
the potential is there to damage your cells as well
Antioxidants
Deactivate reactive molecules
o Without becoming active itself
Can do that by rearranging molecular bond structure of molecule that the reactive molecule took
an H from
So by having lots o
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