The distribution of interleukin-2 receptor bearing lymphocytes in multiple sclerosis: evidence for a key role of activated lymphocytes.

The identification of T cells in the brain using monoclonal antibodies has suggested a role for T cells in the pathogenesis of multiple sclerosis (MS). In the present study the monoclonal antibody anti-Tac, shown to react with interleukin-2 (IL-2) receptors expressed on activated T cells, was used to determine levels of recently activated T cells in blood, cerebrospinal fluid (CSF) and brain sections from MS patients at different stages of disease. The CSF of MS patients contained much higher numbers of IL-2 receptor positive lymphocytes (up to 67%) than blood cells from the same patients, or the CSF of patients with non-inflammatory neurological diseases. In histological sections of the brain of MS patients with active disease, perivascular lymphocytes expressing IL-2 receptors were detected, as were lymphocytes containing IL-2. In contrast, these were absent in brain sections from patients with chronic MS, secondary demyelination or from normal controls. These observations in CSF and brain suggest that in multiple sclerosis, T-cell activation is occurring within the CNS and not in peripheral lymphoid tissue.