Fail to snooze, immune cells lose.

In the bleary-eyed land of the sleep-deprived, the body's immune defenses apparently take a nap. Even relatively modest sleep loss over one night markedly reduces the activity of an important type of infection-fighting immune cell, according to a new report. A good night's sleep restores these cells to their former vigor.

The health implications of such immune losses remain unknown. But the findings add to evidence that "sleep, like fever, may represent a basic host defense mechanism," contend Michael Irwin, a psychiatrist at the San Diego Veterans Affairs Medical Center, and his coworkers. For instance, research on mice and other nonhuman animals suggests that a brief period of sleep deprivation lowers resistance to influenza infection, while sustained sleep loss may bring on

Irwin's team studied 23 healthy men age 22 to 61 who spent certain bacteria-caused illnesses. 4 nights in a sleep laboratory. On the third night, volunteers were denied sleep between 3 a.m. and 7 a.m., losing nearly half their usual slumber time.

The activity of natural killer cells, a type of lymphocyte that helps to fight off viral infections, fell substantially in 18 of the men on the morning after sleep deprivation, the investigators report in the November/December PSYCHOSOMATIC MEDICINE. In fact, compared to the average activity level of these immune cells the day before, activity dropped 30 percent for the entire group after the shortened night's sleep. On the final morning of the study, after volunteers had returned to uninterrupted sleep, natural killer cells bounced back to their former vitality.

Early morning awakening and other sleep problems may contribute to the loss of immune function observed by other researchers (SN: 4/6/91, p.216) in depressed patients and in people who care for spouses with Alzheimer's disease, Irwin's group proposes.