Detection of in vivo stimulated cerebrospinal-fluid lymphocytes by flow cytometry in patients with multiple sclerosis.

To examine the immune response in the central nervous system in patients with multiple sclerosis (MS), we characterized the cell-cycle phase of lymphocytes from cerebrospinal fluid. Cells were stained with acridine orange, and both RNA and DNA content were determined by flow cytometry. Although most cells were in the quiescent phase of the cycle, a significant increase was seen in the percentage of cells in the first stage of the proliferative cycle (G1 phase) when 21 samples of cerebrospinal fluid from 17 patients with MS were compared with samples from 21 controls (P < 0.001). Stimulated cells in the first stage of the cycle were seen in all categories of MS: active, progressive, or stable. In addition, increased numbers of cells in the second stage of the cycle (S phase) were seen in six specimens from patients with MS, five of whom had actie disease, but no increases were seen in controls (P < 0.02). These data indicate that stimulated lymphocytes were present in the cerebrospinal fluid durng all phases of MS and that stimulation becomes more intense during an acute exacerbation.