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Macrophage imbalance (M1 vs. M2) and upregulation of mast cells in wall of ruptured human cerebral aneurysms: preliminary results

David Hasan14*, Nohra Chalouhi2, Pascal Jabbour2 and Tomoki Hashimoto3

Author Affiliations

1 Department of Neurosurgery, Carver College of Medicine, University of Iowa, Iowa City, IA, USA

2 Department of Neurosurgery, Thomas Jefferson University and Jefferson Hospital for Neuroscience, Philadelphia, PA, USA

3 Department of Anesthesia and Perioperative Care, University of California San Francisco, San Francisco, CA, USA

4 Department of Neurosurgery, University of Iowa Hospitals and Clinics, 200 Hawkins Drive, JCP 1616, Iowa City, IA, 52242, USA

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Journal of Neuroinflammation 2012, 9:222  doi:10.1186/1742-2094-9-222

Published: 21 September 2012



M1 and M2 cells are two major subsets of human macrophages that exert opposite effects on the inflammatory response. This study aims to investigate the role of macrophage M1/M2 imbalance and mast cells in the progression of human cerebral aneurysms to rupture.


Ten patients with cerebral aneurysms (five ruptured and five unruptured) underwent microsurgical clipping. During the procedure, a segment of the aneurysm dome was resected and immunostained with monoclonal antibodies for M1 cells (anti-HLA DR), M2 cells (anti-CD 163), and mast cells (anti-tryptase clone AA). A segment of the superficial temporal artery (STA) was also removed and immunostained with monoclonal antibodies for M1, M2, and mast cells.


All ten aneurysm tissues stained positive for M1, M2, and mast cells. M1 and M2 cells were present in equal proportions in unruptured aneurysms. This contrasted with a marked predominance of M1 over M2 cells in ruptured aneurysms (p = 0.045). Mast cells were also prominently upregulated in ruptured aneurysms (p = 0.001). Few M1 and M2 cells were present in STA samples.


M1/M2 macrophages and mast cells are found in human cerebral aneurysms; however, M1 and mast cell expression seems to markedly increase in ruptured aneurysms. These findings suggest that macrophage M1/M2 imbalance and upregulation of mast cells may have a role in the progression of cerebral aneurysms to rupture.

Aneurysm; Inflammation; Macrophages; M1; M2; Mast cells