Analysis of soluble interleukin 6 receptor in cerebrospinal fluid in inflammatory and non-inflammatory conditions

The objective of this study was to investigate the pathophysiological roles of soluble interleukin 6 receptor (sIL-6R) in cerebrospinal fluid (CSF). CSF was obtained from patients suspected with meningitis. Eight patients without any meningeal signs or symptoms were enrolled as controls. An additional 34 CSF samples were collected to measure both biologically active and immunoreactive sIL-6R. All CSF samples were proven to be aseptic. IL-6 and sIL-6R were measured using specific ELISAs. Patients were divided into three groups on the basis of cell number in CSF; inflammatory group (cell number >5 microl, mean 241+/-363.1, n=61); non-inflammatory group (cell number < or =5 microl, mean=2.1+/-1.7, n=12) and controls (cell number < or =5 microl, mean=0.3+1.7, n=8). Among these three groups, the differences in protein (F (2,78)=8.274, P<0.0001) and IL-6 concentration (F (2,78)=6.475, P<0.001) were statistically significant but those of sIL-6R concentration were not. There were only weak correlations between log (sIL-6R) versus log (cell number) (r=0.23, P=0.0375), log (protein) (r=0.239, P=0.0358) and log (IL-6) (r=0.27, P=0.0167). Amounts of immunoreactive and biologically active sIL-6R were closely correlated (r=0.62, n=34, P<0.005). It was concluded that sIL-6R is present constitutively in CSF and its level may not increase significantly in inflammatory conditions; infiltrating cells in CSF are not the main source of sIL-6R; and sIL-6R in CSF can bind IL-6.