Synthesis of the complement factors C3 and C4 within the central nervous system over the course of aseptic meningitis

The concentrations of complement factors C3 and C4 were quantified by single radial immunodiffusion in unconcentrated cerebrospinal fluid (CSF) and in serum from 38 patients up to 2 months after onset of acute aseptic meningitigs (AM). Elevated absolute concentrations were found in CSF in 26 and 35 patients, respectively, and in serum in 8 and 31, respectively. Elevation of the CSF C3 index, equal to (CSF/serum C3):(CSF/serum albumin), and of the corresponding CSF C4 index were found in 16 and 7 patients, respectively, as evidence of intrathecal synthesis. Only minor differences of the frequencies of elevated CSF C3 and C4 indices were encountered over the course of AM up to 2 months after onset. The occurrence of intrathecal C3 and C4 synthesis in AM is proposed as reflecting activation of hitherto unknown significance within the central nervous system.