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Detrimental inflammatory responses in the central nervous system (CNS) are a hallmark of various neurodegenerative pathologies, with multiple sclerosis (MS) and stroke/trauma being excellent examples demonstrating the highly complex interplay between CNS resident microglia and lesion infiltrating leucocytes. Lesion-associated inflammatory responses, both in the acute as well as in the chronic phase, are classified as being highly pro-inflammatory. In this context, it is generally believed that a functional conversion of a pro-inflammatory type M1 microglia/macrophage phenotype, which can readily be detected in severe CNS inflammatory lesions, into a type M2a immune modulating microglia/macrophage phenotype can have a beneficial effect on disease outcome. Using our extensive experience with cell implantation into the CNS of mice, our current research aims at in vivo modulation of neuro-inflammatory responses by intracerebral implantation of mesenchymal stem cells (MSCs) genetically engineered to express interleukin (IL)13, a potent inducer of the M2a phenotype in macrophages. Thus far, we have demonstrated in the cuprizone (CPZ) mouse model of CNS inflammation and demyelination that microglial quiescence and subsequent protection against demyelination coincides with the appearance of M2a-polarised macrophages in the CNS following grafting of IL13-expressing MSCs. Continuing our research, this PhD project will focus on unravelling the in vivo signalling events that lead to IL13-mediated induction of the M2a macrophage phenotype within MSC graft-infiltrating macrophages in the CNS, as well as the cellular interactions by which these M2a macrophages can influence the development of microglia/macrophage-mediated neuro-inflammation in the CNS. Upon completion we hope to: (i) further elucidate the immunological consequences of MSC grafting in the CNS, and (ii) provide pre-clinical rationale for the use of IL13 as an immune modulating cytokine in the CNS.
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