γ δ T cells participate in the immune response against activated, myelin basic protein-specific, human T cells

γδ T cells are over-represented in some multiple sclerosis (MS) parenchymal lesions and in the cerebrospinal fluid (CSF) of individuals with early MS. In this investigation we studied the T cell-T cell interactions between human, myelin basic protein-reactive T cells and peripheral blood mononuclear cells (PBMC) isolated from MS and control subjects. We detected brisk proliferation by PBMC in response to activated, but not resting, MBP-specific T cells. The magnitude of proliferation approached that induced by superantigens and was distinctly greater than the response to standard recall antigens. Examination of the responding T cells revealed predominant expansion of T cells using γδ rather than αβ T cell receptors. This finding suggests that the accumulation of γδ T cells noted in some MS parenchymal lesions may represent recruitment by activation markers expressed by other T cells in these lesions. The response to activated but not resting MBP-specific T cells may parallel observations that protective T cell vaccination in experimental encephalomyelitis is more effective using activated rather than resting, myelin-specific T cells.