Evaluation of bioavailability of three types of IFN beta in multiple sclerosis patients by a new quantitative-competitive-PCR method for MxA quantification

Intracellular expression of human myxovirus protein A (MxA) is exclusively induced by type I IFNs (IFN alpha,beta,omega) or by some viruses and it is strongly increased under IFN treatment. We set up an internally controlled quantitative-competitive polymerase chai n reaction (qc-PCR) that quantifies MxA mRNA expressed in human peripheral blood mononuclear cells (PBMC). Our qc-PCR is accurate because the mean ratio of copy number estimated by q c-PCR to that quantified spectrophotometrically is 1.08 +/- 0.03, moreover it is repeatable with high sensitivity (1 fg MxA/pg GAPDH). MxA mRNA was tested in 47 Relapsing-Remitting Multiple Sclerosis (RR-MS) un treated patients and in 48 patients treated with one of the 3 IFN beta lice nsed for MS (24 with Rebif, 14 with Avonex and 10 with Betaferon). All the 48 treated patients were negative to IFN beta neutralising antibodies (NABs ) as tested in our laboratory using a cytopatic assay (CPE). MxA mRNA levels were detectable in all untreated patients (mean 24 +/- 18 f g MxA/pg GAPDH) and significantly higher levels were found in all the treat ed patients 12 h after IFN beta administration (mean 499 +/- 325 fg MxA/pg GAPDH); furthermore, the three types of IFN beta showed comparable bioavail ability. Our data indicate that the bioavailability of the three available types of IFN beta can be evaluated by MxA qc-PCR, (C) 2001 Elsevier Science B.V. All rights reserved.