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Published on: August 2, 2024
Histological analysis of infiltrating macrophages in the cerebral aneurysm walls
Shigeo Yamashiro1, Hiroki Uchikawa2, Makoto Yoshikawa2
1Division of Neurosurgery, Department of Cerebrovascular Medicine and Surgery, Saiseikai Kumamoto Hospital, Japan.
Abstract:
A series of recent evidences suggested activated macrophages have broadly two distinct forms that possess opposite functions for the process of inflammation: classically activated macrophages (M1/kill macrophages) and alternatively activated macrophages (M2/repair macrophages) according to their functions and expression markers. To elucidate what roles those two phenotypes of macrophages play in the evolution of cerebral aneurysm, the presence of macrophages inside the aneurysm walls was assessed with an immunohistochemical approach. The portions of the aneurysm domes deflated after neck clipping were utilized for the further histological examinations, including immunostainings with five antibodies to identify macrophage subpopulations. In this study, contrary to the previous reports, the following various ratios of subtypes were observed in the aneurysm walls: M1 > M2 (2 cases), M1 < M2 (2 cases), M1 = M2 (3 cases). While M1-like macrophages have been typically regarded as a main driver of the degenerating process, these surprisingly richer presences of M2-like macrophages in the aneurysm walls suggests that an unrecognized biological process might be in play in aneurysm development.
Insights
This study investigated macrophage roles in cerebral aneurysms, finding diverse M1 and M2 macrophage ratios. The significant presence of M2 macrophages suggests novel biological processes in aneurysm development.
Area of Science:
- Neuroscience
- Immunology
- Pathology
Background:
- Activated macrophages exhibit distinct M1 (pro-inflammatory) and M2 (tissue repair) phenotypes.
- Understanding macrophage roles is crucial for elucidating cerebral aneurysm evolution.
Purpose of the Study:
- To investigate the presence and subtypes of macrophages within cerebral aneurysm walls.
- To determine the functional roles of M1 and M2 macrophages in aneurysm pathogenesis.
Main Methods:
- Immunohistochemical analysis of macrophage subpopulations in resected aneurysm domes.
- Utilized five antibodies to identify and quantify M1 and M2 macrophage markers.
Main Results:
- Observed varied ratios of M1 and M2 macrophages in aneurysm walls: M1>M2 (2 cases), M1
- Contrary to expectations, a significant presence of M2-like macrophages was detected.
Conclusions:
- The findings challenge the traditional view of M1 macrophages as the sole drivers of aneurysm degeneration.
- The substantial M2 macrophage presence indicates previously unrecognized biological mechanisms contributing to aneurysm development.
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