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Expert on relationship between animals and bacteria wins Guggenheim honor

June 18, 2009 By David Tenenbaum

University of Wisconsin–Madison developmental biologist Margaret McFall-Ngai has been awarded a prestigious Guggenheim Fellowship, a one-year grant that will support her investigation into how animals interact with their natural complement of microbes.

Along the way, she hopes to explore a theory about the origin of immunity among vertebrates.

McFall-Ngai studies the bobtail squid, which harbors light-emitting bacteria that help it avoid predators. This is symbiosis — a mutually beneficial relationship between two organisms, and McFall-Ngai says symbiosis between animals and bacteria is an emerging and increasingly important aspect of biology. “Your human cells are outnumbered by the bacterial cells in your gut,” she says.

These bacteria are not just residents, but assistants, she says, breaking down food and producing vital chemicals.

This symbiosis raises a question: Conventional wisdom says the immune system is designed to distinguish and attack foreign organisms, yet the bacteria in our intestinal tracts and mouths are seldom under attack. “Immunologists have traditionally thought of the immune system principally as recognizing non-self, but that idea may be too limited,” she says. “Perhaps the immune system also serves to manage the microbes living with us.”

In animals with backbones, the immune systems can “adapt,” to remember disease-causing organisms after infection, and many immunologists believe the adaptive immune system improves our defense against microbes. But the immune system must have sophisticated ways to distinguish between beneficial non-self and pathogenic non-self, says McFall-Ngai. “This function may be managed by the adaptive immune system.

Having an immune system that tolerates beneficial microbes, McFall-Ngai says, gives vertebrates “a selective advantage” that may stem from more efficient use of food. “Now that we know that many animals, including humans, require partnerships with trillions of microbes for their health, we need to figure out how this complexity is managed. A new view of the immune system may be the answer. It would be a very cool thing.”