White blood cells that help heal wounds are showing early promise in rats for treating spinal cord injuries.

They helped the animals regain some leg movement after their spinal cords were severed, researchers report.

That injury normally paralyzes the hind legs permanently. But in many rats that received a dose of their own white cells in their spinal cords when the cut was made, the hind legs could eventually crawl slowly on the knees. The legs usually couldn't support the rats' weight.

The degree of recovery is about equal to what's been achieved before with other techniques, said researcher Michal Schwartz of the Weizmann Institute of Science in Rehovot, Israel. The more interesting thing, she said, is that planting white cells in an injured spine can help it regenerate, much as the cells help heal damage elsewhere in the body.

She stressed that the technique has been tried only in rats, and the recovery is only partial. There is "a long way to go to see whether it works in humans," she said.

She and colleagues report the findings in the July issue of the journal Nature Medicine.

The approach is promising, said Naomi Kleitman of the University of Miami School of Medicine and the Miami Project to Cure Paralysis.

The work is part of a flurry of recent research that shows some recovery with just a small amount of spinal cord regeneration, Kleitman said. Scientists now have to figure out how that happens and whether it can be improved enough to help patients get around, she said.

If so, people would probably be treated with a combination of techniques, she said. Other approaches include building anatomical bridges across injury sites, providing substances to promote regrowth and blocking substances that inhibit regeneration.

Nerve cells through most of the body regenerate if damaged. Nobody knows why spinal nerve cells normally don't. Schwartz believes they don't get enough help from immune-system cells called macrophages, which rush to sites of injury elsewhere in the body, clean up dead cells and debris, and produce substances needed for healing.

So she and colleagues took macrophages, from the rats' blood and stimulated their healing behavior by exposing them to segments of rat leg nerves in the laboratory. Then the researchers severed the animals' spinal cords and planted hundreds of thousands of the stimulated macrophages at the injury site and just next to it.

The first hint of an effect showed up about two months after the injury, Schwartz said, and 15 of the 22 treated rats had partial recovery. Experiments showed that nerve fibers had grown across the injury site, although it's not know just how much regrowth occurred, she said.

Paul Reier, a professor of neuroscience and neurosurgery at the University of Florida College of Medicine in Gainesville, called the work "a significant piece of the puzzle" of how to treat spinal injury.

He noted that the animals were treated immediately after their spinal cords were cut, so it remains to be seen whether the macrophage treatment could help people who've been paralyzed for a long time.

In addition, most human spinal injuries result from crushing rather than complete severing of the spinal cord, so scientists will have to see if the macrophage treatment would help that situation too, he said.