Methods: To examine recruitment of peripheral CD11b+ cells to the brain we developed GFP+ bone marrow (BM) chimeric mouse and exposed these mice to RSD. In the first study enriched CD11b+ cells were isolated from whole brains and GFP+ cells were analyzed using flow cytometry. To establish the location of GFP+ cells a subset of mice were perfused and brains were used for histological analyses. In the second study we exposed IL-1 receptor type-1 deficient (IL-1r1-/-) mice to RSD and enriched brain CD11b+ cells were collected to analyze cellular phenotypes. In addition, GFP+ BM-derived cells from wild-type mice were transferred into IL-1r1-/- mice. Following RSD these IL-1r1-/- chimeric mice were perfused and brains were used for histological analyses.
Results: RSD increased the number of GFP+ cells associated with the brain and these GFP+ cells were predominantly CD11b+ (>85%). GFP+/CD11b+ cells exhibited an inflammatory profile through higher expression of Ly6C. Brains obtained from RSD mice revealed that GFP+ cells were localized in specific stress-responsive brain regions. The GFP+ cells co-localized with Iba-1 immunofluorescence indicating that these cells were derived from a myeloid lineage. Furthermore, the presence of GFP+ cells was absent in the brains of IL-1r1-/- chimeric mice.
Conclusions: RSD induced recruitment of macrophages (CD11b+/Ly6Chigh) to specific regions in the CNS and this was dependent on systemic expression of IL-1r1.