Patients who are NAb+ exhibit decreased benefit from interferon beta (IFN-b), compared to patients who are NAb negative (NAb-).

The IFNB Multiple Sclerosis Study Group reported:8

8-MIU NAb+ patients had relapse rates that resembled placebo rates8 Compared to NAb- patients, NAb+ patients had significantly higher numbers of enlarging MRI lesions8 NAb+ patients showed increased new lesion formation in the MRI8

A NAb assay result, considered in conjunction with clinical activity and MRI evidence, can help to eliminate clinical guesswork that "risks the possibility of removing patients from therapy who remain NAb- and continue to benefit fully from treatment, even if some MS activity may continue."⁵

Recent studies provide new evidence of NAbs modifying the activity of IFN-b.

• "Once NAbs have developed, the bioavailability of IFN beta as measured by MxA is completely inhibited."⁷
• "RRMS patients with higher mean NK cell FA may be not only at greater risk for the development of active lesions but also may be more likely to respond to IFN-b. Development of neutralizing antibodies to IFN-b could interfere with this effect."⁹

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