Reduced in vitro response of CSF lymphocytes to mitogen stimulation in multiple sclerosis.

By means of a microculture technique and calculation of incorporation of 14C-thymidine, cerebrospinal fluid (CSF) lymphocytes from multiple sclerosis (MS) patients showed low or absent proliferation when stimulated with phytohaemagglutinin, concanavalin A, or pokeweed mitogen, in contrast to peripheral blood lymphocytes (PBL) obtained simultaneously and investigated in parallel. A lower proliferation of CSF lymphocytes compared with PBL was also found in acute aseptic meningitis, although it has been reported that CSF lymphocytes show greater proliferation than PBL when specifically stimulated. The low proliferation of MS CSF lymphocytes on mitogen stimulation may be a consequence of prolonged sensitization to an as yet unidentified antigen. The proliferation of MS CSF lymphocytes was not improved by adding irradiated PBL, making helper cell insufficiency less likely. MS CSF had no inhibitory effect on proliferation of PBL, arguing against an inhibitory effect of soluble factors in the CSF as an explanation for the depressed response of CSF lymphocytes.