From the about.com-MS Pages You will find the answer to the Question: What Are Neutralizing Antibodies, Anyway?
Neutalizing Antibodies and Disease-Modifying Therapies for Multiple Sclerosis
How Concerned Should You Be? Neutralizing antibodies (NAbs) are antibodies produced by the body, which react with a foreign agent and destroys it or inhibits its effect. That is great when the “foreign agent” is a virus, and the antibodies work to fight the infection and (in some cases) make you immune to that virus. However, antibodies are not so good when your body is producing them in response to a medication and they are inhibiting the effects of this medication -– in this case an interferon-based disease-modifying therapy. The interferon-based therapies for MS include Avonex, Betaseron and Rebif.