Abstract Body: Background:
Immune responses are fundamental to ischemic stroke pathology. Controlling pro-inflammatory responses helps reduce brain ischemic injury and has translational significance. The interaction between CD200R, an inhibitory receptor on immune cells, and the CD200 ligand suppresses pro-inflammatory pathways. The accumulating data have suggested that CD200R is minimally expressed on adult microglia after stroke, suggesting an inhibitory role of the CD200-CD200R axis in mobilization of peripheral immune cells.
Hypothesis
CD200-CD200R signaling in peripheral leukocytes is more essential than the central (brain) signaling to post-stroke inflammation and outcomes.
Methods:
CD200R global knockout (KO), GFP, and C57BL/6 wild-type (WT) male and female (16-20 months) were used to generate 3 types of bone marrow chimeric (BMC) mice: GFP-to- KO (central signaling), KO-to-GFP (peripheral), and GFP-to-WT (control). All chimeras underwent a 60-minute transient middle cerebral artery occlusion (MCAO). Three days after stroke, neuroinflammation was evaluated by flow cytometry (FC; for leukocyte infiltration), and brain/plasma ELISA (cytokines). Stroke outcomes, including infarct volume and neurobehavioral deficits, were also assessed.
Results
We have validated the three BMC models by FC (Fig. 1). FC analysis further revealed significantly more infiltration of immune cells into ischemic brains of KO-to-GFP vs. control mice; whereas no difference was seen in GFP-to-KO vs. control group. Brain and plasma ELISA data indicated significantly higher levels of pro-inflammatory cytokines (TNF-α, IL-1β) in the KO-to-GFP vs. control mice. Additionally, KO-to-GFP mice demonstrated larger infarct sizes, more severe neurological deficit scores (NDS), and greater motor impairments in the open field test (OFT) and grip strength assessment.
Conclusions
Peripheral CD200R signaling (but not the central signaling) impacts on post-stroke inflammation and outcomes. Our data highlight a potential therapeutic target for mitigating stroke injury by modulating peripheral CD200-CD200R axis.