This study demonstrated that:⁷

• NAbs inhibit the biological IFN-b activity, as measured by MxA levels
• When NAbs were present MxA production was completely inhibited, regardless of NAb titer
• All SBA-negative samples were also NAb negative
• The likelihood of NAbs increase with the SBA titer
• SBA do not appear to influence the bioavailability of IFN-b.
  In NAb negative samples the MxA level did not differ between SBA-positive and SBA-negative samples

The authors suggest that:

[T]he neutralization of IFN-b depends on both the quantity and the quality of antibodies. This phenomenon is poorlyunderstood. One explanation might be that the antibodies bind to different sites at the IFN-b molecule. ... NAb would interfere with the receptor binding sequence of IFN-b, and SBA without neutralization would bind to a more distant site of the molecule.⁷

Though the mechanism of IFN-b neutralization remains unclear, this study provides evidence that, regardless of the mechanism, NAbs eliminate the bioavailability of IFN-b.