Interleukin-6 is elevated in plasma in multiple sclerosis.

Levels of interleukin-6 (IL-6)--a cytokine which induces immunoglobulin production of activated B cells--were measured in cerebrospinal fluid (CSF) and plasma of patients with multiple sclerosis (MS), acute meningo-encephalitis (AM) and muscular tension headache (TH). MS patients had in repeated samples higher levels of IL-6 in plasma compared to patients with AM and TH. IL-6 concentrations in MS plasma were about 17 times higher than MS CSF, while in AM 20-fold higher levels were found in CSF compared to plasma during the acute stage. IL-6 in AM CSF decreased rapidly during clinical recovery. No correlation was found between IL-6 in MS patients' plasma or CSF and disease activity. The functional significance of elevated IL-6 concentrations in MS plasma is unknown, although the findings support the hypothesis of a systemic B cell response in MS.