Q&A with Dr. Bernhard Juurlink, Professor Emeritus (University of Saskatchewan), Director, Canadian Neurovascular Health Society

Q: Is this saying that we need the immune system to clear debris in order for re-myelination to occur? Like the immune system kicks in after a stroke?
http://www.ncbi.nlm.nih.gov/pubmed/25779633

Dr. Juurlink: Some cells have multiple functions. A good example are cells belonging to the mononuclear phagocyte family of cells. This family includes microglia, a cell type that forms approximately 20% of cells in the brain, and blood monocytes, which give rise to macrophages that are found distributed in most tissues. 'Quiescent' mononuclear phagocytes secrete factors that support the functions of adjacent cells. For example, in the CNS, microglia are known to secrete compounds such as Brain-derived Neurotrophic Factor that supports neuronal function - this is an example of a non-immune function of microglia. But activated microglia, like macrophages, can also mop up debris. Microglia can be activated if adjacent cells die via a process known as necrosis. As the microglia digest this debris they present antigens present in this debris to T lymphocytes if they happen to be in the same area - this antigen presentation is a clear immune function. Microglia are actually CNS resident macrophages. Macrophages in other tissues also secrete factors that support adjacent cells, can mop up debris and also present antigens.

The paper by Lampron et al presents data obtained from feeding mice cuprizone, an agent that causes oligodendrocytes to die resulting in demyelination of axons. Normally, microglia would mop up the myelin debris and demyelination occurs. In this set of experiments cuprizone was administered to mice whose microglia were crippled in their ability to mop up debris. One consequence of this failure to mop up myelin debris after cuprizone treatment is a very poor ability to demyelinate.

It is doubtful that this paper has any relevance to MS since there is no evidence that microglia in MS lesions fail to mop up the myelin debris.

You can contact Dr. Juurlink through the CNHS Facebook page (http://www.Facebook.com/CanadianNeurovascularHealth) or directly at bernhard@cnhs.ca


Canadian Neurovascular Health Society

The Canadian Neurovascular Health Society is a registered charity dedicated to improving the lives of Canadians affected by neurovascular diseases, like MS