Deficiency of CD8+ effector memory T cells is an early and persistent feature of multiple sclerosis

Background: Patients with multiple sclerosis (MS) have a deficiency of circulating CD8(+) T cells, which might impair control of Epstein-Barr virus (EBV) and predispose to MS by allowing EBV-infected auto-reactive B cells to accumulate in the central nervous system. Based on the expression of CD45RA and CD62L, CD4(+) T cells and CD8(+) T cells can be subdivided into four subsets with distinct homing and functional properties, namely: naive, central memory, effector memory (EM) and effector memory reexpressing CD45RA (EMRA) cells. Objective: Our aim was to determine which memory subsets are involved in the CD8(+) T cell deficiency and how these relate to clinical course. Methods: We used flow cytometry to analyze the memory phenotypes of T cells in the blood of 118 MS patients and 112 healthy subjects. Results: MS patients had a decreased frequency of EM (CD45RA(-)CD62L(-)) and EMRA (CD45RA(+) CD62L(-)) CD8(+) T cells, which was present at the onset of disease and persisted throughout the clinical course. The frequencies of CD4(+) EM and EMRA T cells were normal. Conclusion: Deficiency of effector memory CD8(+) T cells is an early and persistent feature of MS and might underlie the impaired CD8(+) T cell control of EBV.