David Schneider, PhD, has used used two kinds of bugs (fruit flies and bacteria) to great effect, teasing out intriguing insights into the effects of sleep and caloric intake on response to infection.
Much has been written about the power of the immune system to stave off infectious disease; not so much about the damage the immune response itself can inflict on the organism it's designed to stave. If you've ever ever had influenza, you're well aware of how rotten it made you feel. That was largely a byproduct of your immune response, which, in its zeal to destroy microbial pathogens, often attacks not only infected but healthy tissue. It also raises your body temperature to uncomfortable heights and squirts out inflammatory molecules and oxidants that, while nipping the bug in the bud, may weaken innocent nearby cells and render them more vulnerable to maladies later on.
A delicate balance must be achieved between destroying the invader and sparing the host. To the rescue comes another, less-talked-about aspect of disease control Schneider calls "tolerance" - not to be confused with "immunological tolerance," the willingness of the immune system not to respond with a vengeance to every damned molecule it meets along the way.
For example, an animal may amp up production of anti-oxidant molecules to scavenge free radicals that are released by immune activity in response to an infection. Or, beset by the parasite that causes malaria, it might boost its output of a special molecule that mops up hemoglobin, which, when released from ruptured red blood cells into the circulation, can severely damage tissues.
In a just-out review article in Science, Schneider and two co-authors emphasize the importance of tolerance, a collection of mechanisms that increase an animal's ability to withstand infection independently of its ability to clear the pathogen itself. They write:
The concept of tolerance may... be applicable to the "Typhoid Mary" phenomenon. Healthy carriers that remain asymptomatic despite being infected are likely to have a high level of tolerance to the pathogen with which they are infected.
As above, so below. In the world of one-celled invaders and, unfortunately, in the larger world we inhabit, we sometimes have to fight back even at the cost of considerable damage to the home front. And, in both these worlds, it seems, victory results from a mix of fighting and enduring.