reduced in patients with Alzheimer’s disease [160]. Moreover, resolvin D1 levels significantly correlated with worse Mini-Mental State Examination scores [160], suggesting that the lack of factors to induce M2 polarization has potential functional relevance in human disease. To that end, efforts have been taken to examine different populations of M1 or M2 markers in human Alzheimer’s disease patients. Using several different mRNAs for M2 markers, two different populations can be identified: Alzheimer’s disease brains that are skewed towards M1 and those with an M2a bias [161]. Furthermore, the different populations are associated with different disease stages. In what appears to be early Alzheimer’s disease, there is an M1 bias, while patients with later stage Alzheimer’s disease have an M2a bias. This suggests a potential functional relevance of different microglia populations. However, whether the transition from M1 to M2a is related to disease progression or is simply a response to the enhanced pathology is yet to be understood. Obviously, more work is needed to determine just what these populations represent.
