The first letter states that the changes in T-cell activation markers are transitory and thus preclude using the results of the study in long-term follow-up criteria. We agree that T-cell activation markers are transitory, as they reflect the occurrence of immune activation. As we point out in the article, the correlations between activation markers and MRI are lost when the data are restricted to the monthly time points.1 Regarding the question of whether we have encountered instances of increased activation markers without MRI activity, our findings reflect the statistical probability of detecting a measurable change in activation markers with the appearance of gadolinium-enhancing lesions. This implies that there are occasions when the two events do not occur concurrently. We are not advocating the use of activation marker measurement instead of MRI because the correlations can only be seen when doing frequent measurements and by comparing the changes within each patient.
Khoury SJ, Weiner HL. In reply. Arch Neurol. 2001;58(5):834. doi: