If EBV is actively involved in MS, it would theoretically be consistent with the potentional benfit of PPARgamma agonists.
I can't find any specific studies of the effect of PPARgamma on EBV, but there seems to be general information that PPARgamma suppresses virus replication including HIV, so maybe also for EBV ? That would an interesting one to examine !!
Peroxisome Proliferator-activated Receptor Agonists Inhibit HIV-1 Replication in Macrophages by Transcriptional and Post-transcriptional Effects*
"In addition, there are data in the literature suggesting that natural PPAR agonists suppress replication of viruses other than HIV. PGA is reported to inhibit Sendai virus replication in African green monkey kidney cells (69). PGE1 and PGE2, which can be converted to PGA1 and PGA2, respectively, have also been demonstrated to inhibit measles virus replication in Vero cells (70). Herpes simplex virus replication is reported to be inhibited by PGD2, 7-PGA1, and 12-PGJ2 (71, 72). "