The cerebrospinal fluid C4 complement component in different meningeal and neurological diseases.

The C4 complement component was measured in CSF from 10 patients without CNS involvement (controls) and 71 with various meningeal and neurological diseases. Serum C4 was also measured in the control group and in 46 of the 71 neurological patients. A significant increase of CSF C4 was observed in all neurological diseases with meningeal involvement independent of the causative agent. Inversely, serum C4 values were within normal limits. Increased CSF C4 with normal serum levels might indicate increased diffusion across the blood-brain barrier, decreased ability for immunocomplex production or increased local production.