Follistatin (FS) in human cerebrospinal fluid and regulation of FS expression in a mouse model of meningitis

Objective: Follistatin (FS) is the specific binding protein of activin and expression of both factors is regulated by inflammatory agents. Therefore. FS concentrations were determined in cerebrospinal fluid (CSF) of patients with bacterial and viral meningitis or multiple sclerosis (MS), as well as in the CSF of patients without meningial inflammation or autoimmune diseases. Furthermore, a mouse pneumococcal meningitis model was used to localise the cellular sources of FS in brains of normal and meningitic mice. Methods: FS concentrations in CSF were determined by ELISA; FS in mice was localised by in situ hybridisation and immunohistochemistry. Results: FS concentrations were greater than or equal to0.4 mug/l in 22 of 66 CSF samples of meningitis patients versus 2 of 27 CSF samples from patients with multiple sclerosis (P < 0.05) and 2 of 41 CSF specimen from patients without neuroinflammatory diseases (P < 0.01). In the CSF of patients with meningitis, the concentration of FS was correlated with total protein (P < 0.005) and lactate concentrations (P < 0.05), but not with leukocyte counts, interval between onset of disease and CSF analysis, or clinical outcome. The CSF-to-serum ratios of FS and albumin also correlated significantly (P < 0.0005). in some patients with meningitis the CSF-to-serum ratios suggested that the elevated FS in CSF did not originate from serum alone. FS was localised in mice brains to neurones of the hippocampus, dentate gyrus, neocortex, and to the choroid plexus. Analyses of brains and other organs from uninfected and infected animals sacrificed 6-36 h after infection did not reveal any obvious differences in the distribution and intensity of FS mRNA and protein expression. Conclusions: The concentration of FS in humans is elevated during meningitis. In some patients the increase is caused by a release of FS from brain into CSF. Data from the mouse meningitis model suggest that increased CSF concentrations of FS in meningitis appear not to be accompanied by an elevated number of cells containing FS mRNA or protein in the brain.