Ectopic B lymphocyte follicles exacerbate ischemic brain damage via MIF-CD74/CXCR4 and interferon signaling.

Neuroinflammation, encompassing both innate and adaptive immune responses, plays a crucial role in ischemic stroke. Although B lymphocytes are central to adaptive immunity, their contributions to ischemic stroke remain poorly understood. Here, we demonstrated that B lymphocytes accumulate in ischemic lesions, forming germinal center-like structures at the later stage after stroke, which mainly depended on in situ proliferation. This accumulation correlated with worsened neuroinflammation and ischemic injury, whereas B cell depletion reduced chronic brain damage during stroke. Mechanistically, microglia recruited B cells into ischemic lesions through MIF-CD74/CXCR4 signaling during the early phase of stroke, while IFN-related pathways in B cells further drove neuroinflammation and brain injury. Targeting these pathways markedly alleviated cerebral ischemia and inflammation. Our findings shed light on the role of B lymphocytes in stroke pathology and suggest promising new avenues for therapeutic intervention.