Such an interaction has been shown to promote the activation of microglia in vitro[65] and its genetically engineered or pharmaceutical abrogation results in amelioration of EAE expression.[66] Ponomarev et al. described a two-step process for microglia activation in EAE. They proposed that the CD40-independent first step occurring just before EAE onset is mediated by pro-inflammatory cytokines released by encephalitogenic T cells, such as IFN-γ, and results in Selleckchem CP-690550 microglial cell proliferation and up-regulation of MHC class II, CD40 and CD86; the second step of activation, which is CD40-dependent, occurs at the peak of disease and is characterized by a further
increase in expression of activation markers and a reduced proliferation.[64] Upon full activation, microglia can act as antigen-presenting cells to present phagocytosed myelin antigen to encephalitogenic T cells leading to their expansion in the CNS and severe disease expression.[64] However, antigen presentation
is unlikely to be the main mechanism of damage mediated by microglia in EAE; rather, release of inflammatory cytokines and reactive oxygen species may be more relevant. A recent study identified Peli1, a family member of E3 ubiquitin ligases implicated in TLR and IL-1 receptor signalling in innate immune cells, as an essential regulator of microglia activation during EAE pathogenesis that is required for mitogen-activated protein kinase (MAPK)-dependent production of pro-inflammatory cytokines and chemokines.[67] Peli1 knockout mice Nintedanib (BIBF 1120) were refractory to EAE PD0325901 cost induction and showed reduced numbers of CNS-infiltrating cells and activated resident microglia. Peli1 was abundantly expressed in microglia and absolutely required for microglial activation during EAE, as shown by studies in Peli1-knockout GFP-expressing chimeric mice.[67] In vitro studies showed that Peli1 affects MAPK activation through MyD88-dependent TLR regulation, and acts by promoting
degradation of TNF receptor-associated factor 3, a potent inhibitor of MAPK activation and gene induction.[67] Another molecule that plays an important role in microglia activation leading to neurotoxicity is macrophage migration inhibitory factor (MIF), a pro-inflammatory cytokine identified as a marker of clinical worsening in MS patients.[68] A recent study has shown that MIF can drive the activation of microglia both in vitro in primary microglia cell cultures, and in vivo in EAE-affected mice or in the focal EAE model in MIF-deficient mice.[69] Increasing concentrations of MIF induced dose-dependent changes in expression of inflammatory molecules, such as TNF-α, IL-1β, IL-6 and inducible nitric oxide synthase, in primary microglia in vitro, that were accompanied by morphological changes from resting to activated and/or phagocytic phenotype.