by Greg Miller
As I watched a man two rows ahead of me sniffle and cough
throughout a Tuesday afternoon symposium, I found myself worrying about his
future mental health. After all, I'd just heard talk after talk about how immune
system signaling molecules--like those triggered by infections--can muck with the
brain and cause memory deficits and mood alterations.
Granted, much of this work was done with rodents. Staci
Bilbo of Duke University in Durham, North Carolina, described evidence from her group suggesting that
neonatal rats infected with Escherichia coli bacteria grow up to be poor performers in a
standard test of rat memory. As adults, these animals have abnormally high
numbers of activated microglial cells--the immune system's foot soldiers in the
brain--in the hippocampus, a key memory center. Blocking microglia activation,
Bilbo reported at the meeting, restores normal learning and memory.
Ruth Barrientos of the University of Colorado, Boulder, described findings
from similar experiments with aging rats, suggesting that the very old as well
as the very young may be particularly vulnerable to memory deficits triggered
by infections and the resulting immune system activity.
Perhaps the most disturbing demonstration of the immune
system's potential to influence the brain and behavior was a set of movies
played by Judy Van de Water of the University of California, Davis. Van de
Water is a co-investigator on a large study looking for environmental
and genetic risk factors for autism. She and her colleagues have found that
some mothers of autistic children have antibodies against proteins in the fetal
brain. To investigate whether these antibodies could be interfering with fetal
brain development, the researchers purified antibodies from human mothers of
autistic children and injected them into gestating monkeys.
The movies showed the behavior of two such monkeys as
adolescents. When put in a cage with another, familiar monkey, they didn't interact
and play like monkeys normally do. One repeatedly ran back and forth across the
floor of the enclosure. The other did backflips over and over in a corner.
Although the findings are suggestive, Van de Water noted that only about 17% of
moms of autistic kids in their cohort have tested positive for antibodies
against fetal brain proteins. "It's certainly not what causes all autism,"
The most direct link to human mental health came from psychiatrist
Andrew Miller of Emory University in Atlanta, who described his work with
cancer patients taking immune system activating drugs to fight cancer. In 2001,
Miller and colleagues reported that nearly half of people who take one such
drug, interferon alfa-2b, become depressed within 12 weeks. At the meeting,
Miller presented brain-imaging data suggesting that people taking interferon
alfa have abnormal metabolism in several brain regions important for regulating
arousal and mood. "For us in psychiatry, the idea that infection and the
immune system might come into play in disorders of the brain is one of the most
exciting new ideas to come down the pike in some time," Miller said.