Role of mannose-binding lectin in neutrophil infiltration after traumatic brain injury and brain ischemia

Abstract

Background: Traumatic Brain Injury (TBI) and stroke are leading causes of death and permanent disability worldwide. Following the primary damage, leukocyte infiltration and the complement cascade are recognized as mechanisms involved in secondary brain damage. It has been reported that pharmacological targeting of mannose-binding lectin (MBL), a protein of the lectin pathway of complement activation, is protective in experimental models of acute brain injury. Also, stroke patients carrying genetic MBL deficiency present smaller infarctions and better clinical outcomes. The aim of this study is to investigate the involvement of the lectin pathway in the immune response mediated by neutrophils in mouse models of TBI and stroke.

Methods: Wild-type (wt) and MBL-deficient mice were subjected to controlled cortical impact as a model of TBI or permanent middle cerebral occlusion (pMCAo) as a model of stroke. Cryostat brain sections were obtained and specific staining for neutrophils was carried out at different time points, i.e. 1 (n=xx), 4 (n=xx) and 15 (n=xx) days after TBI or 1 day (n=xx) after pMCAo. We studied neutrophil infiltration and regional location by confocal microscopy, and investigated signs of formation of neutrophil extracellular traps (NETs) by assessing histone 3 citrullination and chromatin decondensation. Cell quantification was carried out in different brain regions (cortex, hippocampus and ventricle).

Results: Both TBI and pMCAo caused neutrophil infiltration. We also detected signs of NETosis in brain infiltrating neutrophils of wt and MBL-deficient mice . Compared to wt mice, MBL-deficient mice showed a reduced number of Ly6G+ neutrophils in the hippocampus and ventricle 4 days after TBI.

Conclusion: These preliminary results suggest that MBL partipates in secondary neutrophil accumulation in the brain lesion. The putative participation of MBL in neutrophil activation and NET formation is under investigation.