Intrathecal origin of CSF ribonuclease. Differences between infectious processes of the nervous system and multiple sclerosis.

A CSF Poly(C)-avid ribonuclease (RNase) activity was determined in serum and CSF of 11 controls and 75 neurological patients (34 multiple sclerosis (MS), 18 infectious processes and 23 other neurological diseases (OND]. In controls, the blood-CSF ratio of RNase activity is low. This fact and the absence of correlation between serum and CSF RNase activity (except in OND group), and between CSF albumin and CSF RNase activity in controls and MS patients, suggest an intrathecal origin for the major part of this CSF RNase activity. A formula taking into account any plasmatic enrichment in RNase of the CSF is proposed to evaluate this intrathecal activity. The normal mean value of this intrathecal RNase activity is 27 +/- 3 units/ml (mean +/- SE) in our experimental conditions and using our formula. The highest intrathecal RNase activity is observed in infectious processes and this finding is associated with a significant increase in the local anti-RNA antibody synthesis. An increase in intrathecal RNase activity is rarely found in MS and local anti-RNA synthesis is only observed in one third of MS patients.