Abstract 3038: Altered Expression Of The Immunomodulatory Proteins Cd200 And Cd200r1 In Lymphoid Tissue Following Ischemic Stroke
Background and Purpose: Previous studies have demonstrated a rapid activation of peripheral immune responses following experimental stroke, marked by increases in pro-inflammatory cytokines, chemokines, and leukocyte entry into the brain, which may exacerbate tissue damage caused by reperfusion. In the CNS, a consequence of the local immune response to stroke is disruption of the immunosuppressant interaction between CD200 ligand (CD200), expressed by CNS-resident cells, and CD200 receptor (CD200R1) on microglia. Microglia are myeloid-derived cells, which serve as endogenous macrophages within the CNS. In models of CNS injury, disruption of the CD200-CD200R1 interaction leads to changes in intracellular signaling that can increase expression of several pro-inflammatory factors. In the present study, we compared gene expression of CD200 and CD200R1 in the bone marrow, a site of immune cell production, between sham and stroke mice. Additionally, we explored CD200 and CD200R1 protein expression in the primary and secondary lymphoid tissues between sham and stroke mice.
Methods: Experimental stroke was induced by middle cerebral artery occlusion in male C57BL/6 mice for 90 minutes prior to reperfusion. Mice were sacrificed 5, 24, and 72 hours after stroke. Bone marrow was harvested from femur and RNA was extracted using Trizol®. cDNA was analyzed for CD200 and CD200R1 expression using qPCR. Western blots were performed on protein extracts from spleens and lymph nodes.
Results: In the 5-hour cohort, a significant increase in CD200R1 and CD200 expression was observed in the bone marrow of stroke mice compared with sham. Expression of CD200 and CD200R1 was also elevated in secondary lymphoid tissue in stroke mice. In the 72-hour cohort, a significant decrease in CD200 expression was observed in stroke mice compared to sham mice. Within lymphoid tissue, similar trends were also observed for CD200R1.
Conclusions: Immediately following stroke injury, CD200 and CD200R1 gene expression levels are altered in bone marrow, thereby enhancing pro-inflammatory signaling and increasing immune cells in peripheral circulation that can migrate into the brain. The subsequent decrease in expression of these proteins in the 72-hour cohort suggests that CD200- and CD200R-expressing cells are depleted in the bone marrow as a result of their activation, mobilization, and recruitment to the brain. Increased CD200 and CD200R expression in the spleen suggest a similar response by the peripheral immune system as the brain signals for the production of anti-inflammatory components. These results suggest that following stroke, bone marrow activation induces a mobilization signal which targets CD200/R-expressing cells to sites of ischemic brain injury, and is consistent with previous observations showing increased CD200R1 protein levels in the brain following stroke.
- © 2012 by American Heart Association, Inc.