Microglia to the rescue

Immune cells fight a losing battle against a harmful abnormal protein found in some cases of amyotrophic lateral sclerosis (ALS), as Kang and Rivest report. The findings support the hypothesis that extracellular accumulations of faulty proteins trigger the disease's neural damage.

Researchers aren't sure why muscle-controlling motor neurons deteriorate in ALS. Patients with the inherited form of the disease carry mutations in the gene for the antioxidant enzyme SOD1. But how defective SOD1 causes neurodegeneration remains uncertain. One possibility is that the altered SOD1 builds up outside neurons and eventually kills them. Several studies suggest that some neighboring cells can shield neurons from the protein's ill effects. Kang and Rivest tested whether microglia, the main infection-combating cells in the brain, were protective.

The researchers transplanted bone marrow...