Immune T Cells Involved in Parkinson's Disease
Lymphocytes CD4+ Mediate Cytotoxicity and Cell Death in the Brain
Jan 2, 2009
Parkinson's disease, often characterized by tremor, is a neurodegenerative disorder that impairs movement, balance, coordination and speech. In general Parkinson's disease is a sporadic condition of unknown cause that may affect more than 1 million people in USA. This disease is due to the loss, or cellular death, of neurons that produce a substance called dopamine in particular area of the brain called substantia nigra. For other details on Parkinson's disease see also this article or this article.
Immune cells accumulate in the brain of Parkinson's Patients
It was already known since 1988 from a study published by McGeer et al., that the loss of dopamine-containing nerves is accompanied by accumulation, in the substantia nigra, of white blood cells known as T lymphocytes or T cells (Ann Neurol 24, pp574-576, 1988). Until now, these accumulating T cells were not thought to have a role in the development of disease.
The immune system contains several groups of immune cells with very specific functions. A major group of immune cells is called lymphocytes. There are two classes of lymphocytes: T lymphocytes and B lymphocytes responsible of different immune functions. T lymphocytes are again sub-divided in several subclasses depending of their specific role in the imnune system. The two main subclasses are called CD4+ T helper cells and CD8+ cytotoxic cells. The first class, the CD4+ T cells, is the target of the HIV virus, causing AIDS.
Immune Cells are Involved in the Development of Parkinson Disease
French researchers, Vanessa Brochard, Stéphane Hunot, Etienne C. Hirsch, and colleagues, from INSERM UMR 679 and University of Pierre et Marie Curie (Paris, France), show that CD4+ T cells, a subclass of T lymphocytes, are strongly involved in the development of the Parkinson's disease in a mouse model. The study , "Infiltration of CD4+ lymphocytes into the brain contributes to neurodegeneration in a mouse model of Parkinson's disease", has been published online in December 2008 in the prestigious scientific journal Journal of Clinical investigation (2008, vol , pp).
In their study, the french researchers have observed a substantial number of CD4+ T cells and CD8+ T cells in postmortem brain tissue of individuals with Parkinson's disease as well as in mice with a Parkinson-like disease. Interestingly, mice lacking T cells, CD4+ and CD8+, developed substantially less severe Parkinson-like disease. Further analysis indicated that this protection was specifically associated with the lack of CD4+ T cells expressing a protein called FasL.
Immune Cells Can Protect and Attack the Brain
Surprisingly, this study shows that immune cells can have protective and destroying effects on the cells of the brain. Although, further analyzes are needed to confirm these observations and particularly the importance of CD4+ T cells in human Parkinson's disease, this study suggests that targeting the immune system might provide a new therapeutic avenue to treating Parkinson's disease.
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