Parenchymal accumulation of CD163+ macrophages/microglia in multiple sclerosis brains

Reactive macrophages/microglia exert both protective or damaging effects in multiple sclerosis (MS), which contribute to the relapsing–remitting nature of MS. CD163 is considered a marker of M2 (alternatively activated) macrophages. In the MS brain, CD163+ perivascular macrophages express molecules for antigen recognition and presentation. Here we further investigated the accumulation of CD163+ macrophages/microglia in the parenchyma of MS brains. CD163 expression pattern was investigated in different lesions of brain tissue specimens from five MS brains and five neuropathologically unaffected controls by immunohistochemistry. In the parenchyma of normal brain samples, immunoreactivity (IR) of CD163 was absent. In acute active lesions and at the rim of chronic active lesions of MS, strong accumulation of CD163+ macrophages/microglia was seen. In chronic inactive lesions and in the center of chronic active lesion, CD163+ macrophages/microglia were rare. Further, double-labeling showed that parenchymal and perivascular CD163+ macrophages/microglia were myelin basic protein positive and HLA-DR+, suggesting that CD163+ macrophages/microglia could ingest and present antigen. In addition, in vitro incubating macrophage RAW264.7 cells with myelin turned LPS-induced inflammatory macrophages into an anti-inflammatory phenotype, indicating that myelin basic protein positive, CD163+ macrophages/microglia in MS might have anti-inflammatory effects. The parenchymal CD163+ macrophages/microglia, which had the capacity for antigen ingestion and presentation, might contribute to the resolution of inflammation in MS.