Glucocorticoids Regulate Bone Marrow B Lymphopoiesis After Stroke

Rationale: After stroke, patients frequently experience altered systemic immunity resulting in peripheral immunosuppression and higher susceptibility to infections, which is at least partly attributed to lymphopenia. The mechanisms that profoundly change the systemic leukocyte repertoire after stroke are incompletely understood. Emerging evidence indicates that stroke alters hematopoietic output of the bone marrow. Objective: To explore the mechanisms that lead to defects of B lymphopoiesis after ischemic stroke. Methods and Results: We here report that ischemic stroke triggers brain-bone marrow communication via hormonal long-range signals that regulate hematopoietic B lineage decisions. Bone marrow FACS analyses and serial intravital microscopy indicate that transient middle cerebral artery (tMCA) occlusion in mice arrests B cell development beginning at the pro-B cell stage. This phenotype was not rescued in Myd88-/- and TLR4-/- mice with disrupted Toll like receptor signaling or after blockage of peri...