TLR4 and Gliosis: Exposure to metals such Lead (Pb), Methyl mercury (MeHg), Vanadium (V), Tin Oxide (TO) results in gliosis by activating Toll-like receptor 4 (TLR4) -myeloid differentiation primary response 88 (MyD88) -nuclear factor (NF)-κB signaling cascade, increasing receptor phosphorylation and the activation of Mitogen-activated protein kinase (MAPK) cascades with subsequent initiation of signal transduction some of which are responsible for the production of pro-inflammatory cytokines (218, 234–236).