Open Access Research

Cerebral inflammation and mobilization of the peripheral immune system following global hypoxia-ischemia in preterm sheep

Reint K Jellema12, Valéria Lima Passos3, Alex Zwanenburg114, Daan RMG Ophelders12, Stephanie De Munter12, Joris Vanderlocht59, Wilfred TV Germeraad69, Elke Kuypers12, Jennifer JP Collins29, Jack PM Cleutjens7, Ward Jennekens1011, Antonio WD Gavilanes12, Matthias Seehase12, Hans J Vles8, Harry Steinbusch1, Peter Andriessen1011, Tim GAM Wolfs29 and Boris W Kramer129*

Author Affiliations

1 School of Mental Health and Neuroscience, Maastricht University, Universiteitssingel 40, Maastricht, 6229 ER, The Netherlands

2 Department of Pediatrics, Maastricht University Medical Center, PO box 5800, Maastricht, 6202 AZ, The Netherlands

3 Department of Methodology and Statistics, Maastricht University, P. Debyeplein 1, Maastricht, 6229 HA, The Netherlands

4 Department of Biomedical Technology, Maastricht University, Universiteitssingel 50, Maastricht, 6229 ER, The Netherlands

5 Department of Transplantation Immunology, Tissue Typing Laboratory, Maastricht University Medical Center, PO box 5800, Maastricht, 6202 AZ, The Netherlands

6 Department of Internal Medicine, Division of Haematology, Maastricht University, Universiteitssingel 50, Maastricht, 6229 ER, The Netherlands

7 Department of Pathology, Maastricht University Medical Center, PO box 5800, Maastricht, 6202 AZ, The Netherlands

8 Department of Child Neurology, Maastricht University Medical Center, PO box 5800, Maastricht, 6202 AZ, The Netherlands

9 School of Oncology and Developmental Biology, Maastricht University, Universiteitssingel 50, Maastricht, 6229 ER, The Netherlands

10 Neonatal Intensive Care Unit, Maxima Medical Centre, De Run 4600, Veldhoven, 5504 DB, The Netherlands

11 Department of Clinical Physics, Maxima Medical Centre, De Run 4600, Veldhoven, 5504 DB, The Netherlands

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Journal of Neuroinflammation 2013, 10:13  doi:10.1186/1742-2094-10-13

Published: 24 January 2013

Abstract

Background

Hypoxic-ischemic encephalopathy (HIE) is one of the most important causes of brain injury in preterm infants. Preterm HIE is predominantly caused by global hypoxia-ischemia (HI). In contrast, focal ischemia is most common in the adult brain and known to result in cerebral inflammation and activation of the peripheral immune system. These inflammatory responses are considered to play an important role in the adverse outcomes following brain ischemia. In this study, we hypothesize that cerebral and peripheral immune activation is also involved in preterm brain injury after global HI.

Methods

Preterm instrumented fetal sheep were exposed to 25 minutes of umbilical cord occlusion (UCO) (n = 8) at 0.7 gestation. Sham-treated animals (n = 8) were used as a control group. Brain sections were stained for ionized calcium binding adaptor molecule 1 (IBA-1) to investigate microglial proliferation and activation. The peripheral immune system was studied by assessment of circulating white blood cell counts, cellular changes of the spleen and influx of peripheral immune cells (MPO-positive neutrophils) into the brain. Pre-oligodendrocytes (preOLs) and myelin basic protein (MBP) were detected to determine white matter injury. Electro-encephalography (EEG) was recorded to assess functional impairment by interburst interval (IBI) length analysis.

Results

Global HI resulted in profound activation and proliferation of microglia in the hippocampus, periventricular and subcortical white matter. In addition, non-preferential mobilization of white blood cells into the circulation was observed within 1 day after global HI and a significant influx of neutrophils into the brain was detected 7 days after the global HI insult. Furthermore, global HI resulted in marked involution of the spleen, which could not be explained by increased splenic apoptosis. In concordance with cerebral inflammation, global HI induced severe brain atrophy, region-specific preOL vulnerability, hypomyelination and persistent suppressed brain function.

Conclusions

Our data provided evidence that global HI in preterm ovine fetuses resulted in profound cerebral inflammation and mobilization of the peripheral innate immune system. These inflammatory responses were paralleled by marked injury and functional loss of the preterm brain. Further understanding of the interplay between preterm brain inflammation and activation of the peripheral immune system following global HI will contribute to the development of future therapeutic interventions in preterm HIE.

Keywords:
Hypoxic-ischemic encephalopathy; Inflammation; Microglia; Neutrophils; Oligodendrocytes; Preterm; Spleen