Overactive immune systems — not weakened ones, as conventionally believed — could make the elderly more prone to viral infections, Yale School of Medicine researchers have discovered.

The study — from a research team led by Daniel Goldstein, an associate professor of internal medicine and cardiology at the School of Medicine — shows that the immune systems of elderly mice infected with the herpes virus mistakenly attack healthy liver cells as well, said Heather Stout-Delgado, a post-doctoral fellow at the School of Medicine who designed and conducted the experiments.

In elderly mice between 18 and 20 months old, immune system cells released excess amounts of the inflammatory chemical interleukin 17, which caused white blood cells to kill liver cells, in turn causing all the mice to die. The immune systems of mice between the ages of 2 to 4 months released less interleukin 17, and none of the young mice died.

When researchers gave the aged mice an anti-inflammatory drug which reduced their interleukin 17 levels, all of them survived, said lab member Anushree Shiralli.

While scientists have long known that elderly people are more susceptible to viral infections, Goldstein said, previous studies showed that aged mice had weakened, not excessively strong, immune responses to viral infections.

“(The study) indicated that exaggerated or imbalanced immune responses contribute to death with aging rather than what was previously known, which typically was that declining immunity explained impairments in response to infection with age,” Goldstein said.

Goldstein said the results of the study indicate that anti-inflammatory drugs could help the elderly to overcome viral infections.

Goldstein and his team will next study whether their results apply to infections in other organs, such as the lungs. The team will also look at immune reactions to the flu among the elderly.

“We assume that a lot of the immune responses in elderly are augmented and have deleterious effects in the aged host,” Stout-Delgado said.

The study was funded by the National Institute on Aging, and the anti-inflammatory drugs were provided by the biotechnology company Amgen. Other researchers involved with the study were Yale researchers Wei Du and Carmen Booth.

The results of the study were published in the Nov. 19 issue of Cell Host & Microbe journal.