The immune system protects us from scores of invaders, but it can also turn against us when white blood cells called autoimmune T cells attack the body's own tissue. But now it appears that these renegades may come to our rescue after nerve injury. The findings, reported in the current issue of Nature Medicine, could lead to new treatments for strokes and spinal cord injuries.
To prevent collateral damage to precious nerve cells during immune skirmishes, the brain and spinal cord are tightly sealed off from the rest of the body by the blood-brain barrier. Yet autoimmune cells occasionally slip past this barrier, sometimes with devastating results: In multiple sclerosis (MS), for instance, these cells destroy the nerve fibers' protective sheath, crippling their victims. The same cells, mysteriously, have been found on occasion in the central nervous system of healthy people. Six months ago, Michal Schwartz and her team at the Weizmann Institute of Science in Rehovot, Israel, showed that another type of white blood cell called a macrophage can help damaged spinal nerves grow back. She wondered if rogue T cells might perform a similar job inside this inner sanctum.
Schwartz cultured T cells that trigger a condition similar to MS in rats, then injected these immune cells into rats immediately after crushing their optic nerves. When nerve cells are injured so severely, surrounding cells also die off in the hours after the trauma. Two weeks after the rats sustained their injuries, Schwartz's group found that the number of surviving cells in the damaged nerves of these rats was three times higher on average than in rats with similar damage that received a placebo injection. "The revolution here is that the autoimmune response is not always bad," she says. "It may be a normal physiological response to damage."
It's unknown why some autoimmune cells would come to the rescue in emergencies, while others ravage vital tissue. As they explore this mechanism, Schwartz hopes there may be ways in the meantime to recruit the "good" autoimmune T cells. If she succeeds, says neuroimmunologist Howard Weiner of the Center for Neurologic Disease at Harvard Medical School in Boston, the cells could perhaps be enlisted in strokes, spinal injuries, and other conditions marked by heavy neuron loss immediately following an accident.