382 Differential Modulation of Skull Macrophages and Monocytes by Indoles in Germ-Free and Aged Mice Post-Stroke

INTRODUCTION: The role of skull bone marrow in cerebrovascular disease has not been well studied. We hypothesized that post-stroke indole treatment would modulate immune responses differently in germ-free (GF) and aged non-germ-free (non-GF) mice. METHODS: We used a reversible middle cerebral artery occlusion (MCAO) model in aged (18 months) wild-type (WT) male mice to investigate the effects of indoles. GF and aged non-GF mice were treated with either indoles or vehicle post-stroke. Flow cytometry assessed the percentage of skull macrophages and monocytes (CD45+CD11b+) and the mean fluorescence intensity (MFI) of CD80, a co-stimulatory molecule critical for immune activation. RESULTS: We found that after MCAO in aged mice, indoles significantly increased the percentage of skull macrophages (32.9% ± 2.35) compared to the vehicle group (26% ± 1.27; p = 0.032), while there was no significant difference in monocyte percentage between indoles (94.85% ± 0.7) and vehicle (95.33 ± 0.5; p = 0.62). Additionally, there was no significant reduction in CD80 MFI with indoles (5790 ± 375) compared to vehicle (6786 ± 434; p=0.11). In GF mice, there was no significant change in the percentage of skull macrophages between indoles (31.3% ± 2.35) and vehicle (32.9% ± 2.07; p = 0.64). However, indoles significantly decreased the percentage of skull monocytes (93% ± 0.877) compared to vehicle (95.36% ± 0.48; p = 0.047) and significantly reduced CD80 MFI (3759 ± 139) compared to vehicle (4756 ± 178; p = 0.001). CONCLUSIONS: Indole treatment induces distinct immunomodulatory effects in GF and aged non-GF mice post-stroke. These findings highlight the critical role of microbiota in mediating the immune-modulatory effects of indoles in post-stroke neuroinflammation.