Through either blocking receptor interaction or inhibiting signal transduction, neutralizing antibodies (NAbs) "are capable of reducing or abrogating the normal biological and treatment effects of interferons."²

NAb status (positive or negative) is determined by measuring, through an assay, the receptor blocking effect caused by NAbs.

NAbs develop early in IFN-b therapy. A study by the IFNB Multiple Sclerosis Study Group showed that "for the most part, NAb development is a first-year phenomenon."⁸

In this study, the percentage of antibody-positive (at least two consecutive titers at 20 NU/ml) patients in the 8-MIU IFN-b-1b (therapeutic dose level) treatment arm was as follows:
	0-6 months:	15%
	7-12 months:	31%
	13-18 months:	36%
	19-24 months:	38%
	25-30 months:	39%

Clinical data from IFN-b trials showed NAb formation in a subset of patients:

5% of patients who were on Avonex® (IFN-b-1a), for up to 18 months were NAb positive (NAb+)4 26% of patients who were on Betaseron® (IFN-b-1b) for up to 18 months were NAb+4

Clinical Effects
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