To investigate T cell and antibody immunity to Epstein–Barr virus (EBV) in multiple sclerosis (MS).

Immunoglobulin G (IgG) immunity to EBV nuclear antigen 1 (EBNA1) and viral capsid antigen was measured by enzyme linked immunosorbent assays, and T cell immunity was assessed using enzyme linked immunospot assays to measure the frequency of peripheral blood mononuclear cells (PBMC) producing interferon γ in response to autologous EBV infected B cell lymphoblastoid cell lines (LCL) in 34 EBV seropositive healthy subjects and 34 EBV seropositive patients with MS who had not received immunomodulatory therapy in the previous 3 months.

Patients with MS had increased levels of anti-EBNA1 IgG but a decreased frequency of LCL specific T cells compared with healthy subjects. Using purified populations of CD4⁺ T cells and CD8⁺ T cells, we showed that the LCL specific response resides predominantly in the CD8⁺ population, with a frequency 5–7-fold higher than in the CD4⁺ population. The decreased CD8⁺ T cell response to LCL in MS was not caused by decreased HLA class I expression by LCL, and LCL from MS patients could be killed normally by HLA matched EBV specific cytotoxic CD8⁺ T cell clones from healthy subjects. Furthermore, the decreased CD8⁺ T cell immunity to EBV was not due to a primary defect in the function of CD8⁺ T cells because EBV specific cytotoxic CD8⁺ T cell lines could be generated normally from the PBMC of patients with MS.

This quantitative deficiency in CD8⁺ T cell immunity to EBV might be responsible for the accumulation of EBV infected B cells in the brains of patients with MS.