Cerebral and peripheral amyloid phagocytes--an old liaison with a new twist.

In this month's issue of Nature Medicine, Town et al. suggest that peripheral macrophages invading the brain reduce cerebral amyloidosis and thus may play a key role in the pathogenesis of Alzheimer's disease (AD). This observation intensifies the longstanding controversy of whether mononuclear cells such as macrophages and/or microglial cells are beneficial or detrimental in AD.