New data reported at the ACTRIMS Forum (West Palm Beach, FL, USA, 29 February–2 March 2024) add to growing evidence of an aetiological role for Epstein–Barr virus (EBV) infection in multiple sclerosis (MS). Fumie Hayashi presented a study that identified clonally expanded EBV-specific CD8+ T cells in the cerebrospinal fluid (CSF) of people with MS.

MS lesions contain large numbers of T cells, in particular those expressing the CD8 antigen. These cells are difficult to study in situ in living individuals, but the CSF provides a reliable surrogate measure of their abundance in the brain.