Examining post-mortem tissue from the brains of people with Alzheimer's disease, investigators identified what appear to be iron-containing microglia -- specialized scavenger cells that sometimes become inflammatory -- in a particular part of the hippocampus, a key brain structure whose integrity is critical to memory formation.
In post-mortem brain tissue from people not diagnosed with Alzheimer's, neither the iron deposits nor the scavenger cells engulfing them were present in that brain region.
The findings, recounted in a study published in Neurobiology of Aging. 
 Surprisingly, in the brain region of interest there was no consistent overlap between the iron-laden microglia and the amyloid plaques or tau. The bulk of microglia found in association with iron in the study were in an activated, inflammatory state.
The researchers noted that this was a preliminary study performed on a small number of human brain specimens, which are generally difficult to obtain.
"Some imaging studies using mouse models of Alzheimer's disease had revealed the presence in these mice's brains of tiny, mysterious black dots that could signal the presence of iron, an element that shows up dark under MRI and, in certain chemical forms, can be highly reactive and inflammation-inducing," author said. 
http://med.stanford.edu/news/all-news/2015/07/iron-containing-inflammatory-cells-seen-in-alzheimers-brains.html