Early neutrophil infiltration is critical for inflammation-sensitized hypoxic-ischemic brain injury in newborns

Abstract

Neutrophils are the most abundant leukocytes and usually the first immune cell-type recruited to a site of infection or tissue damage. In asphyxiated neonates, elevated peripheral neutrophil counts are associated with poorer neurological outcomes. Induced neutropenia provides brain protection in animal models of neonatal hypoxic-ischemic (HI) injury, but the anti-neutrophil serum used in past studies heavily cross-reacts with monocytes, thus complicating the interpretation of results. Here we examined neutrophil influx and extravasation, and used a specific anti-Ly6G antibody for induced neutropenia against lipopolysaccharide (LPS)-pretreated HI injury in murine neonates, a model for inflammation-sensitized hypoxic-ischemic encephalopathy (HIE). As early as 6 h after the LPS/HI insult, the mRNAs for neutrophil-recruiting and mitogenic chemokines ascended in the ipsilateral hemisphere, coinciding with immuno-detection of neutrophils. However, neutrophils mainly resided within blood vessels, exhibiting signs for neutrophil extracellular traps (NETs), before 48 h post-LPS/HI. Prophylactic anti-Ly6G treatment blocked the brain infiltration of neutrophils, but not monocytes or lymphocytes, and markedly decreased LPS/HI-induced pro-inflammatory cytokines, matrix metalloproteinase 9 (MMP-9), and brain tissue loss. In contrast, anti-Ly6G treatment at 4 h post-LPS/HI failed to prevent the influx of neutrophils and brain damage. Together, these results suggest important pathological functions for early-arriving neutrophils in inflammation-sensitized HIE.

Dynamic capillary stalls in reperfused ischemic penumbra contribute to injury: A hyperacute role for neutrophils in persistent traffic jams

“…Indeed, in a murine model of neonatal hypoxic-ischemic encephalopathy and lipopolysaccharide challenge, early prophylactic targeting of Ly6G-positive neutrophils prevented neutrophil-associated inflammatory activity and brain damage, while delayed treatment several hours after ischemia was not effective. 66 In line with this recent study that did not evaluate blood flow, our findings indicate a possible contribution of early temporal flow heterogeneity introduced into the microcirculation by neutrophils to the ultimate functional outcome. This suggestion is based on the improvement of capillary flow dynamics as early as 2 h after reperfusion by neutrophil targeting, which is reflected positively to the corresponding capillary oxygenation profile.…”

Altered distributions and functions of natural killer T cells and γδ T cells in neonates with neonatal encephalopathy, in school-age children at follow-up, and in children with cerebral palsy

“…Neonates with NE have increased numbers of monocytes and neutrophils with dysregulated functions (Morkos et al, 2007;O'Hare et al, 2016) and elevated serum levels of inflammatory cytokines, which are associated with poor developmental outcomes and mortality (Bajnok et al, 2017;O'Hare et al, 2017;Perrone et al, 2018). The importance of neutrophils in brain injury following hypoxia ischemia is clear from animal studies, where neutrophil depletion can reduce brain injury (Doycheva et al, 2014;Yao and Kuan, 2020). The serum cytokine levels in the subjects in the present study are consistent with a role for neutrophils in NE.…”

Resolvin D1 ameliorates Inflammation-Mediated Blood-Brain Barrier Disruption After Subarachnoid Hemorrhage in rats by Modulating A20 and NLRP3 Inflammasome

“…Microglia and neutrophils are key immune cells involved in the inflammatory response in CNS inflammation-related diseases, such as hypoxic-ischemic brain injury and SAH (Z. Xu et al, 2019b ; Yao and Kuan, 2020 ). FPR2, a member of the G protein-coupled receptor family, plays an important role in host defense and cellular debris clearance ( Weiss and Kretschmer, 2018 ).…”