The placebo effect during a double blind trial of recombinant alpha 2 interferon in multiple sclerosis patients: immunological and clinical findings.

A double-blind, placebo controlled trial of recombinant alpha 2 interferon in relapsing/remitting multiple sclerosis patients was performed to assess the clinical and immunological responses to treatment. This study demonstrated that natural killer (NK) cell activity, known to be enhanced by interferon (IFN) treatment, increased during the first week of treatment in both the IFN and placebo treatment groups. After the first week of treatment NK cell activity returned to baseline levels in both groups, and subsequently declined in the IFN treatment group. Patients in both groups improved clinically, as evidenced by a reduction in the exacerbation rate. Furthermore, a similar incidence of adverse reactions to treatment were reported by both groups. The mechanism underlying the response to placebo is not known. However, it is unlikely that the long term clinical improvement (one year) in either group is related to the transient increase in NK cell activity.