Infiltrating gamma delta T cells are potentially involved in the central nervous system demyelination in multiple sclerosis (MS). To further study this hypothesis, we analyzed the frequency and functional properties of gamma delta T cells in peripheral blood (PB) and paired cerebrospinal fluid (CSF) of patients with MS and control subjects, including patients with other neurologic diseases (OND) and healthy individuals. The frequency analysis was performed under limiting dilution condition using rIL-2 and PHA. After PHA stimulation, a significantly increased frequency of gamma delta T cells was observed in PB (14.7 x 10(-4)) and in CSF (15.8 x 10(-4)) of MS patients as compared with 4.3 x 10(-4) in PB and 3.9 x 10(-4) detected in CSF of patients with OND. The frequency was represented equally in OND patients and normal individuals. Similarly, the IL-2-responsive gamma delta T cells occurred at a higher frequency in PB of control subjects (1.1 x 10(-4)) in OND patients and 1.5 x 10(-4) in normal individuals). Forty-three percent (13 of 30) of the gamma delta T cell clones isolated from PB and CSF of MS patients responded to heat shock protein (HSP70) but not HSP65, whereas only 2 of 30 control gamma delta T cell clones reacted to the HSP. The majority of the gamma delta T cell clones were able to induce non-MHC-restricted cytolysis of Daudi cells. All clones displayed a substantial reactivity to bacterial superantigens staphylococcal enterotoxin B and toxic shock syndrome toxin-1, irrespective of their gamma delta V gene usage. Furthermore, the gamma delta T cell clones expressed predominantly TCRDV2 and GV2 genes (26 of 35 clones), whereas the clones derived from CSF of MS patients expressed either DV1 or DV2 genes. The obtained gamma delta clones, in general, represented rather heterogeneous clonal origins, even though a predominant clonal origin was found in a set of 10 gamma delta clones derived from one patient with MS. The present study provides new evidence supporting a possible role of gamma delta T cells in the secondary inflammatory processes in MS.