Regarded as a damaging reaction, innate immune response can either improve or worsen brain outcome after injury. Hence, inflammatory molecules might modulate cell susceptibility or healing events. The remyelination that follows brain lesions is dependent on the recruitment of oligodendrocyte progenitor cells (OPCs) and expression of genes controlling differentiation and myelin production, such as Olig1 and Olig2 bHLH transcription factors. We aimed to determine how innate immunity affects these processes. Here we report that lipopolysaccharide (LPS) infusion triggered OPC reactivity. Acute inflammation changed the distribution of Olig1- and Olig2-expressing cells following chemical demyelination, enhanced reappearance of transcription signals linked to remyelination and rapidly cleared myelin debris. Although cells expressing Olig1, Olig2, and proteolipid protein were attracted to demyelinated sites in the course of chronic inflammation, myelin loss was not associated with the effects of inflammation on OPC reactivity. In addition, the beneficial properties of brain immunity are broadened to an aggressive model of injury, wherein LPS through Toll-like receptor 4 (TLR4) reduced surfactant-mediated damage while anti-inflammatory treatment enlarged the lesion. In conclusion, TLR4 activation in microglia is a powerful mechanism for improving repair at the remyelination level and protecting the cerebral tissue in presence of agents with strong cytolytic properties.

Key words: lipopolysaccharide • toll-like receptor 4 • demyelination • Olig bHLH transcription factors • neuroprotection.