T Cell deficiency may explain Multiple Sclerosis virus link

Evidence that MS patients are deficient in the T cells that normally control Epstein-Barr virus may help explain the pathogenesis of the disease, Australian researchers say.

Professor Michael Pender and colleagues at the Royal Brisbane and Women’s Hospital found the average percentage of CD8 T cells was significantly decreased in the blood of MS patients compared with healthy subjects.

They also made the “striking” discovery that the proportion of CD8 T cells declined markedly with age in MS patients compared with healthy controls, based on their study of 64 MS patients and 68 healthy age and sex-matched subjects.

Reporting their findings in a letter in the Journal of Neurology, Neurosurgery and Psychiatry, they wrote: “What is remarkable about the CD8 T cell deficiency in MS is that normally when EBV load is increased, as it is in the blood and brain of MS patients, the CD8 T cell frequency should increase and not decrease.

“This suggests that there is a fundamental defect in the ability of MS patients to make an appropriate CD8 T cell response to EBV.”

Speaking with Neurology Update, Professor Pender said CD8 T cell deficiency in MS was first reported three decades ago, but had been “largely forgotten”.
In the meantime, increasing evidence had suggested EBV had a role in MS.

Bringing these two ideas together, he suggested CD8 T cell deficiency might contribute to the lack of control of EBV in MS patients, and to the development of the disease.

“More work will be needed to confirm it and determine what’s causing the deficiency in the first place. We believe it’s genetically determined but that needs to be worked out,” he said.

The researchers also tested the frequency of peripheral blood mononuclear cells producing IFN-ɣ in response to autologous EBV-infected B cell lymphoblastoid cell lines (LCL).

They found that for a given percentage of CD8 T cells in the blood, the LCL-specific T cell frequency in MS patients was generally lower than in healthy subjects.

This, they said, indicated that the decreased LCL-specific T cell frequency in MS was due to the CD8 T cell deficiency.

Sources: J Neurol Neurosurg Psychiatry & Neurology Update (09/08/11)