These findings suggest that CCR2+ macrophages recruited into the peripheral nerves from the blood exert neuroprotective functions on the lower motor neurons in mSOD1 ALS and that the clearance of abnormal mSOD1 protein from peripheral nerves by these cells is a hitherto underestimated host protective mechanism (Supplementary Fig. 6). The gene discussed is CCR2; the disease is amyotrophic lateral sclerosis.