Fig. 1.

Opposing molecular factors in demyelinated lesions. In the context of multiple sclerosis, the myelin sheaths are attacked by autoimmune reactive cells. The concomitant pro-inflammatory situation is leading to a glial activation of astrocytes and microglial cells contributing to the secretion of various molecular signals. On the one side, growth factors and chemokines are positively acting on the recruitment of oligodendrocyte precursor cells (OPCs) attracted towards the lesion in order to repair myelin. On the other side, repulsive growth inhibitory molecules accumulating in this perturbed microenvironment create a molecular barrier preventing OPCs to reach the centre of the lesion hence precluding myelin repair