Macrophages are comprised of resident brain microglia not infiltrating peripheral monocytes acutely after neonatal stroke

Abstract

Macrophages can be both beneficial and detrimental after CNS injury. We previously showed rapid accumulation of macrophages in injured immature brain acutely after ischemia-reperfusion. To determine whether these macrophages are microglia or invading monocytes, we subjected post-natal day 7 (P7) rats to transient 3 h middle cerebral artery (MCA) occlusion and used flow cytometry at 24 and 48 h postreperfusion to distinguish invading monocytes (CD45high/ CD11b+) from microglia (CD45low/medium/CD11b+). Inflammatory cytokines and chemokines were determined in plasma, injured and contralateral tissue 1-24 h post-reperfusion using ELISA-based cytokine multiplex assays. At 24 h, the number of CD45+/CD11b+ cells increased 3-fold in injured compared to uninjured brain tissue and CD45 expression shifted from low to medium with less than 10% of the population expressing CD45high. MCA occlusion induced rapid and transient asynchronous increases in the pro-inflammatory cytokine IL-b and chemokines cytokine-induced neutrophil chemoattractant protein 1 (CINC-1) and monocyte-chemoattractant protein 1 (MCP-1), first in systemic circulation and then in injured brain. Double immunofluorescence with celltype specific markers showed that multiple cell types in the injured brain produce MCP-1. Our findings show that despite profound increases in MCP-1 in injured regions, monocyte infiltration is low and the majority of macrophages in acutely injured regions are microglia. Keywords: cytokines, flow cytometry, inflammation, macrophage, microglia, neonatal stroke. Inflammation is a significant contributing factor to neurodegenerative diseases. Depending on injury setting, the relative involvement of systemic and local inflammation, and communication between the two compartments can vary (Carson and Sutcliffe 1999;Baggiolini 2001;Perry 2004). It is well known that stroke in adult triggers a robust inflammatory reaction, largely involving an influx of peripheral leukocytes into the brain parenchyma (for reviews, see Feuerstein et al. 1997;Dirnagl et al. 1999;Han and Yenari 2003) and disruption of the blood-brain barrier (BBB) (Gidday et al. 2005). In the adult, neutrophils are typically the first leukocyte type to infiltrate (Barone et al. 1991;Garcia et al. 1994;Matsuo et al. 1995) and are followed by macrophages and lymphocytes (Barone et al. 1991;Garcia et al. 1994). The damaging role of infiltrating neutrophils in ischemia was shown by studies in which neutrophil depletion (Garcia et al. 1994) or administration of anti-adhesion molecules (Kishimoto and Rothlein 1994;Fassbender et al. 1999) reversed the reduced local tissue perfusion, BBB disruption, and the release of free radicals, proteinases, and other cytotoxins seen after stroke. The key role of macrophages in cerebral ischemic injury has also been firmly established (Feuerstein et al. 1997;Dirnagl et al. 1999;Han and Yenari 2003). Macrophage populations in the injured brain, however, are diverse (Carson et al. 1998;Dalmau et al. 2003) Abbreviations used: BBB, blood-bra...

Resident microglia, rather than blood‐derived macrophages, contribute to the earlier and more pronounced inflammatory reaction in the immature compared with the adult hippocampus after hypoxia‐ischemia

“…Moreover, we showed that blood‐derived macrophages began infiltrating the hippocampus in the P9 pups 1 day after HI, but few blood‐derived macrophages infiltrated the hippocampus of the 3mo mice at the same time point. Denker et al reported that the population of blood‐derived macrophages (CD45 high macrophages) in the injured hemisphere 24 hours after HI of P7 rats was 8.8 ± 6.7% and the majority of macrophages were resident microglia (CD45 low and CD45 med macrophages) as judged by flow cytometry (Denker et al, 2007), which is consistent with our results. CCL2 has been reported to increase BBB permeability in vivo (Stamatovic et al, 2005).…”

Minocycline Reduces Neuronal Death and Attenuates Microglial Response after Pediatric Asphyxial Cardiac Arrest

“…suggesting an important role for microglia in ACA-induced neurodegeneration in PND17 rats. Hypoxic-ischemic insults induce proinflammatory cytokine production in both adult and immature brain (Cowell et al, 2002;Denker et al, 2007;Gregersen et al, 2000;Jander et al, 2002). These cytokines can contribute to secondary neurotoxicity or exacerbate ischemic brain damage by recruiting inflammatory cells such as microglia, macrophages, and neutrophils (Kriz, 2006;Minami and Satoh, 2003;Trendelenburg, 2008).…”

Neurodegeneration Induced by PVC-211 Murine Leukemia Virus Is Associated with Increased Levels of Vascular Endothelial Growth Factor and Macrophage Inflammatory Protein 1α and Is Inhibited by Blocking Activation of Microglia

“…For example, in a rat model for acute stroke, increased MCP-1, IL-1␤, and CINC-1 were associated with activated microglia prior to neuronal damage (8). Mice infected with the neurovirulent MuLV FrCasE showed increased levels of MIP-1␣ and MIP-1␤ early in the course of disease (3), while mice infected with the neurovirulent polytropic MuLV Fr98 showed increased expression of TNF-␣, TNF-␤, IL-1␣, MIP-1␣, MIP-1␤, MCP-1, IP10, and RANTES (37).…”