Abstract TP266: Ischemic Stroke Induces Striking Heterogeneity in the Inflammatory Leukocyte Infiltrate Across the Core and Penumbra

Abstract

Background: Current therapies for ischemic stroke focus on reperfusion but do not address the acute inflammatory response. Previous clinical trials aimed at modulating the inflammatory milieu by disrupting leukocyte infiltration failed to show clinical efficacy. One possible explanation for this unexpected shortcoming is an incomplete understanding of the precise spatio-temporal underpinnings of leukocyte extravasation and infiltration. Methods: Here we describe the evolution of the inflammatory response in a mouse transient middle cerebral artery occlusion (tMCAO) stroke model at 0, 1, 2 and 3 days post reperfusion. We used wide field and confocal immunofluorescence microscopy to examine the exact nature and location of the invading myelomonocytic populations, with close examination of the leukocyte position with regard to the brain vasculature and the perivascular space. Results: Our findings suggest that the vast majority of infiltrating myelomonocytic cells escape the perivascular compartment and enter the parenchyma. Interestingly, leukocyte extravasation and accumulation in the subcortex occurred over several days. Dramatic heterogeneity in the inflammatory infiltrate was observed across the infarcted tissue, but also in the surrounding penumbra and adjacent cortical surface. In addition, triphenyl tetrazolium chloride staining, a common indicator for infarcted tissue, did not correlate with the amount or location of leukocyte infiltration. Conclusion: Taken together our findings demonstrate that the infiltration of leukocytes dynamically evolves over several days following reperfusion. Furthermore, leukocytes infiltrate in a heterogeneous pattern that does not correlate well with traditional markers of cellular dysfunction. A better understating of the precise spatio-temporal infiltration of inflammatory cells could help inform the next generation of therapeutic interventions.