Decreased CD8+ T cell response to Epstein-Barr virus infected B cells in multiple sclerosis is not due to decreased HLA class I expression on B cells or monocytes

Background: Patients with multiple sclerosis (MS) have a decreased frequency of CD8(+) T cells reactive to their own Epstein-Barr virus (EBV) infected B cells. We have proposed that this might predispose to the development of MS by allowing EBV-infected autoreactive B cells to accumulate in the central nervous system. The decreased CD8(+) T cell response to EBV results from a general CD8(+) T cell deficiency and also a decreased proportion of EBV-specific T cells within the total CD8(+) T cell population. Because decreased HLA class I expression on monocytes and B cells has been reported in MS and could influence the generation and effector function of EBV-specific CD8(+) T cells, the present study was undertaken to measure the expression of HLA molecules on B cells and monocytes in patients with MS. Methods: We used flow cytometry to determine the proportions of T cells, natural killer cells, B cells and monocytes in peripheral blood mononuclear cells (PBMC) and to quantify the expression of HLA molecules on T cells, B cells and monocytes of 59 healthy subjects and 62 patients with MS who had not received corticosteroids or immunomodulatory therapy in the previous 3 months. Results: The levels of HLA class I and class II molecules expressed on T cells, B cells and monocytes were normal in patients with MS, with the exception of two patients with secondary progressive MS with very low class II expression on B cells. In confirmation of previous studies we also found that the percentage of CD8(+) T cells was significantly decreased whereas the percentage of CD4(+) T cells and the CD4:CD8 ratio were significantly increased in patients with MS compared to healthy subjects. Conclusions: The decreased CD8(+) T cell response to EBV-infected B cells in MS patients is not due to decreased HLA class I expression on monocytes or B cells. In a small proportion of patients decreased HLA class II expression on B cells might impair the CD8(+) T cell response to EBV by reducing CD4(+) T cell help.