Abstract TMP77: Iga+ B Cells Are Recruited To The Brain After Intracerebral Hemorrhage

Abstract

Introduction: There is ample evidence of a B cell response in human stroke patients, and evidence that long-term cognitive decline is linked to ongoing B cell activation in ischemic stroke models in mice. However, the role of B cells in hemorrhagic stroke, particularly at late timepoints, is unknown. Methods: Intracerebral hemorrhage (ICH) was induced in 12-week male C57BL/6 mice by collagenase (or saline for sham controls) injection into the striatum. Mice were perfused 2, 4, or 8 weeks post-ICH or sham, ipsilateral and contralateral hemispheres were harvested and B cell counts analyzed by flow cytometry. Motor deficits were measured via grid walk test and short-term memory was tested by Y maze at 1, 2, 4, 8, 12, and 16 weeks post-ICH or sham. B cell repertoire analysis was conducted by PCR amplification and molecular cloning of B cells in 8 week post-ICH or naïve brain tissue, followed by Sanger sequencing and comparison to the IMGT database. Results: B cells are robustly recruited to the ipsilateral hemisphere as early as 2 weeks post-ICH (2439 +/- 987 cells; n=5) and persist at 8 weeks (14,162 +/- 12,103 cells, n=4). At 2 and 4 weeks a small fraction of B cells in the ipsilateral hemisphere are IgA+ (2 weeks=14.0% +/- 6.8%, n=5; 4 weeks=13.3% +/- 4.6%, n=3). Interestingly, by 8 weeks post-ICH this proportion significantly increased in ICH (41.3% +/- 22.8, n=6) but not sham controls (12.0% +/- 11.8%, n=5). While our work has demonstrated no significant motor deficit after 2 weeks post-ICH, preliminary data suggests a cognitive short-term memory deficit starting 16 weeks post-ICH. Furthermore, we have found that post-ICH brain-infiltrating IgA+ B cells are somatically hypermutated and show diverse V gene usage. Conclusion: Our findings suggest that ICH induces a robust, delayed IgA+ B cell response within the affected brain hemisphere, underscoring the need to better understand how B cells shape post-stroke inflammation and recovery, particularly at late timepoints.