Objective: To correlate Mx protein (Mx) levels in lysed blood leukocytes with the clinical response to interferon (IFN) beta-1b (IFNbeta-1b) in relapsing-remitting MS (RR-MS) patients for monitoring treatment.

Background: Intracellular Mx expression is exclusively induced by the type I IFNs (IFN-alpha, -beta, and -omega) or by viruses and is strongly increased under IFN treatment. Quantitative determination of Mx allows objective assessment of biological effects of IFN.

Methods: Mx protein levels were measured in blood leukocyte lysates from IFNbeta-1b-treated RR-MS patients by ELISA and correlated to clinical parameters, including relapse rate and clinical deterioration.

Results: In stable IFNbeta-1b-treated MS patients, Mx levels were significantly increased compared to patients with or without immunosuppressive treatment. In IFN-1b-treated MS patients during relapse, Mx levels were significantly lower than during stable phases of the disease. Mean values of Mx (MVMx) over time of treatment in patients with a reduction of relapse rate were significantly higher than in patients without response.

Conclusions: Mx levels in lysed blood cells may represent a useful surrogate marker for IFNbeta-1b activity corresponding to the clinical response during treatment of MS.