Daclizumab-induced increased frequencies of circulating CD56bright NK cells were related to the therapeutic benefit of the drug . Likewise, during therapy with IFNb, the total number of circulating natural killer cell declined slightly  or did not change  but there was a marked increase in the proportion of CD56high NK cells in both 12 month follow up studies. One of the possible mechanisms of action of IFN-β in MS is the enhancement of NK activity, especially CD56bright NK cells . Given this finding, the analysis of NK cells seems to be a good predictive factor, in particular in combination with CD56bright subset analysis.