Neutralizing antibodies, MxA expression and MMP-9/TIMP-1 ratio as markers of bioavailability of interferon-beta treatment in multiple sclerosis patients: a two-year follow-up study.

Background:  The objective of this study was to correlate the detection of neutralizing antibodies (NAbs) by the cytopathic effect (CPE) assay, with the expression of myxovirus resistance protein A (MxA), and the ratio between matrix metalloproteinase 9 (MMP-9) and its tissular inhibitor (TIMP-1), in order to evaluate their usefulness as markers of interferon beta (IFN-beta) bioavailability. Methods:  Pairs of blood and serum samples were collected from 50 patients with multiple sclerosis (MS) during 2 years of IFN-beta treatment. Expression of MxA, MMP-9 and TIMP-1 were analysed by quantitative PCR, and NAbs were measured by CPE assay. Results:  During the study, 60% of patients presented NAbs. The number of serum samples that were NAbs+ was significantly increased amongst patients with relapses (41/92 vs. 33/108, P = 0.04). With one serum sample and with a NAb titre >100 tenfold reduction unit (TRU), 66.7% of patients with MS suffered from relapses, 41.7% suffered from progression, and 75% was not an optimal clinical responder. We did not find any significant difference in MxA. We found that 62.5% of patients with MS patients whose ratio was increased twofold after 2 years suffered from relapses, 37.5% suffered from progression, and 68.7% was not an optimal clinical responder. Conclusion:  The early detection of NAbs by CPE assay and the finding of only one serum sample with a NAb titre >100 TRU seem to be markers of low bioavailability of IFN-beta, whilst a twofold decrease in the MMP-9/TIMP-1 ratio by quantitative PCR assay seems to be a marker of high bioavailability of IFN-beta.