Increased levels of antiviral MxA protein in peripheral blood of patients with A chronic disease of unknown etiology*

Abstract Interferon alpha (IFN‐α) is synthesized in response to viral infections. MxA protein, induced specifically by IFN‐α and β, expressed in peripheral blood cells, is detected more consistently than circulating IFN‐α in serum of patients with viral infections. Thus, activation of the IFN‐α/MxA system can be used as additional marker of the presence of a virus in patients. Therefore MxA protein and IFN‐α levels were measured in patients with multiple sclerosis (MS), a chronic neurological disease of unknown etiology, in order to investigate the possible role of viruses in the expression of this disease. The means of MxA values obtained by using an immunochemiluminescent assay were significantly higher in blood of patients with remitting (n = 197) or relapsing (n = 39) multiple sclerosis (MS) patients and in patients with viral infections than in blood from healthy controls (n = 25) and from patients with bacterial infections (n = 12). Intra‐individual variance in MxA levels in seven clinically stable remitting patients with MS was observed in the course of a follow‐up, and high MxA levels were detected in three of them in blood samples collected consecutively over several months. By using an ultra sensitive assay, a higher MxA‐inducer activity was obtained with sera from MS patients (n = 39) than with those from healthy controls (n = 12). Experiments with neutralizing antibodies proved that this activity in serum from patients was due to IFN‐α, whereas IFN‐α could not be detected by other methods. Altogether these results demonstrate that there is an activation of the IFN‐α/MxA system in MS patients, which is consistent with the hypothesis that a viral infection may be associated with MS. J. Med. Virol. 65:301–308, 2001. © 2001 Wiley‐Liss, Inc.