Intrathecal production of neopterin in aseptic meningo-encephalitis and multiple sclerosis.

Neopterin levels in cerebrospinal fluid (CSF) and serum were measured with a sensitive radioimmunoassay in patients with multiple sclerosis (MS), aseptic meningo-encephalitis (AM), other mostly non-inflammatory neurological diseases, and controls with tension headache or psychoneurosis. Elevated levels of neopterin were found in CSF in most patients during acute phase of AM, and normalization after clinical recovery. The elevation in CSF was not reflected in serum. Only four of 24 MS patients--three of them examined during exacerbation--had slight elevation of neopterin in CSF and all had normal serum levels. Neopterin levels in CSF correlated with mononuclear cell count. The elevation of neopterin observed in CSF in inflammatory CNS diseases despite low cell numbers in CSF compared to blood might reflect a high activation level of cells locally in the CNS. Neopterin in CSF is a valuable marker of acute cellular immune response.