Fans of The Three Stooges may remember the episode in which Curly asks Moe what he wants to eat. Moe responds, "Four pieces of burnt toast and a rotten egg." Why did he say this? Because Moe had a "tapeworm and it's good enough for him." Little did Moe know that he was actually dispensing profoundly deep immunological wisdom.
This week, scientists from the University of Michigan and the University of Manchester reported in the journal PLoS Pathogens
that, when faced with a parasitic infection, a mouse's immune system will purposefully cause it to undereat (i.e., "hypophagia"). To show this, they infected normal mice and mice that had various immunological deficiencies with the roundworm Trichinella spiralis.
(This parasite causes trichinosis, an infection associated with undercooked pork.)
The researchers demonstrated that a mouse infected with T. spiralis has a two-phase hypophagic response. Both phases of reduced eating were dependent on a functioning adaptive immune response (which generates antibodies). Mice that lacked an adaptive immune response ate normally. That might not sound like a terrible thing, but it didn't work out well for the mice.
Typically, when mice don't eat, blood levels of a metabolism-regulating hormone called leptin decrease. Leptin also happens to regulate the immune response. With less leptin around, the mouse is able to direct its immune system toward producing antibodies. But if levels of leptin are too high, the mouse appears less able to do that.
Connecting all this, the authors hypothesized that leptin was the key factor. They believe that mice purposefully quit eating so that their leptin levels drop, allowing the mouse to generate a robust antibody response against the parasite. To test this, they injected leptin into mice infected with T. spiralis. Just as they expected, the mice had a very difficult time fighting off the parasite.
Altogether, the researchers demonstrated that undereating is not just a side effect of parasitic infection; instead, it is vital to fighting off the worm.
And you thought there was no intellectual value in watching The Three Stooges. Nyuk nyuk nyuk.
(This post is dedicated to my dad, who still watches Moe, Larry and Curly.)
: Worthington JJ, Samuelson LC, Grencis RK, McLaughlin JT (2013) Adaptive Immunity Alters Distinct Host Feeding Pathways during Nematode Induced Inflammation, a Novel Mechanism in Parasite Expulsion. PLoS Pathog 9(1): e1003122. doi:10.1371/journal.ppat.1003122
(Image: Trichinella spiralis via Wikimedia Commons)