No abstract

Microglia and infiltrating macrophages are thought to orchestrate the central nervous system (CNS) response to injury; however, the similarities between these cells make it challenging to distinguish their relative contributions. We genetically labeled microglia and CNS-associated macrophages to distinguish them from infiltrating macrophages. Using single-cell RNA sequencing, we describe multiple microglia activation states, one of which was enriched for interferon associated signaling. Although blood-derived macrophages acutely infiltrated the demyelinated lesion, microglia progressively monopolized the lesion environment where they surrounded infiltrating macrophages. In the microglia-devoid sciatic nerve, the infiltrating macrophage response was sustained. In the CNS, the preferential proliferation of microglia and sparse microglia death contributed to microglia dominating the lesion. Microglia ablation reversed the spatial restriction of macrophages with the demyelinated spinal cord, highlighting an unrealized macrophages-microglia interaction. The restriction of peripheral inflammation by microglia may be a previously unidentified mechanism by which the CNS maintains its “immune privileged” status.

Reactive gliosis is a characteristic response of astrocytes to inflammation and trauma of the central nervous system. To investigate whether soluble factors (cytokines) from inflammatory mononuclear cells that accumulate at lesion sites can provide the cellular signals to initiate gliosis and to identify such cytokines, we have tested and found that supernatants derived from subsets of activated human T lymphocytes (CD8' or CD41) are potent mitogens for cultured human adult astrocytes. This effect is blocked by a neutralizing antibody to -interferon (IFN). Recombinant A consideration in relating relevance of in vitro proliferation results to reactive gliosis in vivo is that gliotic scars seldom develop after insults to the embryonic brain (22-24) but are common features in adult brain injuries. Thus, it becomes important to assess proliferation of astrocytes derived from adult animals, rather than from neonatal ones. We have adopted such a strategy by using adult human astrocytes isolated from surgical brain biopsies and have addressed the following questions. Do activated human T lymphocytes produce sufficient cytokines to induce proliferation of cultured adult human astrocytes; if so, which cytokine (s) (see Results), were treated with trysin and seeded on poly(L-lysine)-coated (10 jag/ml) 9-mm Aclar fluorocarbon coverslips at 10,000 cells per coverslip. These mixed cells were used for the present study; methods for eliminating microglia from rodent glia cultures (leucine methyl ester and silica ingestion) (28-30) were not effective for human preparations. Culture medium was Eagle's minimum essential medium supplemented with 5% (vol/vol) fetal calf serum, Gentamicin (20 gg/ml), and dextrose (1 mg/ml) (all from GIBCO).

No abstract

The prognosis of intracerebral haemorrhage continues to be devastating despite much research into this condition. A prominent feature of intracerebral haemorrhage is neuroinflammation, particularly the excessive representation of pro-inflammatory CNS-intrinsic microglia and monocyte-derived macrophages that infiltrate from the circulation. The pro-inflammatory microglia/macrophages produce injury-enhancing factors, including inflammatory cytokines, matrix metalloproteinases and reactive oxygen species. Conversely, the regulatory microglia/macrophages with potential reparative and anti-inflammatory roles are outcompeted in the early stages after intracerebral haemorrhage, and their beneficial roles appear to be overwhelmed by pro-inflammatory microglia/macrophages. In this review, we describe the activation of microglia/macrophages following intracerebral haemorrhage in animal models and clinical subjects, and consider their multiple mechanisms of cellular injury after haemorrhage. We review strategies and medications aimed at suppressing the pro-inflammatory activities of microglia/macrophages, and those directed at elevating the regulatory properties of these myeloid cells after intracerebral haemorrhage. We consider the translational potential of these medications from preclinical models to clinical use after intracerebral haemorrhage injury, and suggest that several approaches still lack the experimental support necessary for use in humans. Nonetheless, the preclinical data support the use of deactivator or inhibitor of pro-inflammatory microglia/macrophages, whilst enhancing the regulatory phenotype, as part of the therapeutic approach to improve the prognosis of intracerebral haemorrhage.