November 28, 2002
By Adrian Burton
Special to DG News
Highly reactive astrocytes located in newly developing multiple sclerosis (MS) plaques, and on the rims of established plaques might be responsible for initiating autoimmune reactions.
"Most people who work on MS focus on microglia as the main type of cell responsible for immunological reactions, but we thought that astrocytes might also be very important, at least in antigen presentation," explained Esther Zeinstra, Neurologist at the University Hospital, Groeningen, The Netherlands, spoking here November 28 at the European Charcot Foundation Symposium.
"Like microglia, astrocytes express major histocompatibility complex class II molecules on their surface, which are required for cells to present [auto]antigens to T cells," Dr. Zeinstra explained. "But they are not the only thing needed to get a full blown immunological reaction. You also need co-stimulation, but until now it was thought astrocytes did not express co-stimulatory molecules. However, we have found that, in some cases, they do."
Using white matter samples from 20 MS patients, 10 controls and a further two patients with herpes simplex encephalitis, the Dutch team performed double immunofluorescent staining for microglia and astrocytes and the T cell co-stimulatory molecules B1-7 and B7-2.
No co-stimulatory molecules were found on astrocytes in samples from herpes simplex encephalitis or control patients. However, some of the astrocytes in samples from the MS patients clearly stained for both co-stimulators. "Not all of them showed this, just the very reactive, very swollen ones in newly formed plaques or on the rims of established plaques. They seem to express them at this point in the disease process," explained Dr. Zeinstra.
Interestingly, the microglia of the control patients also expressed both major histocompatibility complex class II and the co-stimulatory molecules, raising the question of whether microglia are actually involved in MS at all.
"Astrocytes are worth looking at further to see whether they have a
larger role than we have recognised up to now. If they have, it could open
up new therapeutic options," concluded Dr. Zeinstra.
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