DiagnosticsDiet Restriction Can Lead To Unwanted Changes In Immunity
Why do animals lose their appetites when sick? Should this inform our
understanding of diet restriction therapies intended to increase lifespan?
In
this week"s issue of the online open access journal PLoS Biology,
scientists at Stanford University report another step taken towards
understanding
the link between immunity and aging.
Individuals can evolve two ways of surviving infections; they can resist
the invading microbe by killing it, or they can tolerate the microbe and
simply not become ill as microbe numbers rise. Most animals become
anorexic (lose their appetites) when they are infected, but the effects
this has
on the host isn"t well understood. Does the anorexia help the animal
survive the infection or is it simply an unfortunate side effect? This
story
is complicated by the science of aging and diet restriction; moderate diet
restriction appears to increase the lifespan of laboratory animals. Will
medical treatments that mimic diet restriction and attempt to increase our
lifespan interfere with this immune-regulated feeding response? "The
answer seems to depend upon the infecting pathogen," argues senior author
Dr David Schneider, of the Department of Microbiology & Immunology at
Stanford University.
"We used infected fruit flies (Drosophila melanogaster) to answer these
questions. We found that flies become anorexic when infected with some
bacteria. To see how this anorexia might affect the fly"s immune response
we used two tricks. The first was to use a fly with a mutant taste
receptor - this fly appears not to like the taste of fly food and doesn"t
eat much. We also limited the flies" diets by diluting their food. We
found that diet restriction altered the fly"s immune response and affected
both resistance and tolerance. The fly became more tolerant of
Salmonella infections, which suggests that anorexia could be a good thing
that helps a host survive an infection. However, we found that diet
restriction caused the flies to turn off an immune response that was
critical for resisting Listeria infections and thus the flies died rapidly
when
infected with this microbe. "
These results provide one explanation for how anorexia might help an
infected fly - the fly is better at tolerating the infection. These
results
suggest that diet restriction treatments will have complicated
interactions with infections; they may help the infected animal survive
some infections
but can be deleterious in others. "Diet restriction might become a useful
tool once we can determine the rules governing its interactions with
different pathogens; however, diet restriction should be applied
cautiously because it is clear, at least in flies, that diet restriction
can lead to
unwanted changes in immunity," Schneider concludes.
Funding: This work was funded by a National Science Foundation Graduate
Research Fellowship, National Institutes of Health grant 1RO1AI069164, and
an
Ellison Medical Foundation Senior Scholar"s Award in Aging. The funders
had no role in study design, data collection and analysis, decision to
publish, or preparation of the manuscript.
Competing interests statement: The authors declare that no competing
interests exist.
Citation:
"The Role of Anorexia in Resistance and Tolerance to Infections in Drosophila."
Ayres JS, Schneider DS (2009)
PLoS Biol 7(7): e1000150. doi:10.1371/journal.pbio.1000150
PLoS Biology