Sci. Aging Knowl. Environ., 12 May 2004
Learning Is in the Blood
Weakening the immune system saps brainpower
A well-tuned immune system not only rebuffs noxious invaders but keeps the brain sharp, a new study suggests. The work shows that hobbling the immune system in mice impairs learning and memory. The results raise the possibility that enhancing immunity might bolster brain acuity in illnesses such as Alzheimer's disease (AD) and stave off the mental declines of aging.
Researchers have long known that the brain influences the immune system, but they are just beginning to unravel how the immune system adjusts the workings of the brain. T cells and other immune system cells can infiltrate the organ and release molecules that alter nerve transmission and behavior. Some studies have suggested a link between T cells and mental acuity. Last year immunologist Rita Effros of the University of California, Los Angeles, and colleagues nabbed immune cells from AD patients and measured the length of telomeres, the chromosome caps that limit cells' reproductive life spans. The longer the T cell telomeres, the better a patient scored on a cognitive test. Pinning down how these cells affect mental abilities is important in part because they often malfunction with age (see "Immunity Challenge").
To further analyze interactions between the brain and T cells, neuroimmunologist Michal Schwartz of the Weizmann Institute of Science in Rehovot, Israel, and colleagues measured how well mice without a functioning immune system learned the location of a submerged rest platform in a tank of water. The immune-impaired mice took longer than control rodents to find the platform and couldn't recall its position from one day to the next. These experimental mice lacked B cells as well as T cells, so the team also tested a line of mice that have no T cells but are otherwise immunologically intact. The rodents also floundered, but their scores climbed after they each received a T cell infusion. The researchers then dosed normal mice with one of two drugs that, among other effects, makes rodents forgetful in the water tank. Mice that also received a compound called copolymer-1 that prods T cells retained their mental sharpness. Together, the results suggest that depleting T cells undermines learning and memory and that stimulating the cells prevents the loss. "Boosting the immune system might be a way for the brain to recharge itself," says Schwartz. Jump-starting T cells might help save the faculties of patients with diseases such as AD and keep our minds keen as we age, she says.
The finding is exciting "and opens major new approaches to neuroimmunology," says Effros, but "it's not totally unexpected to think that the immune system can affect cognitive function apart from AD." "It's a very exciting paper," says neuroscientist Steven Zalcman of the University of Medicine and Dentistry of New Jersey in Newark. But just stimulating the immune system won't guarantee better thinking, he says. As we age, some parts of the immune system become hyperactive, which can also wreak havoc. Stimulating T cells and quenching other immunological activities might be the trick for keeping our brains in shape.
May 12, 2004
Science of Aging Knowledge Environment. ISSN 1539-6150