**7. Conclusion**

In demyelinating diseases, mainly in relapse phase of RRMS, the BBB suffer a profound disturbance, so as the exchanges and ultimately the CNS itself. Despite CNS suffered an immune response, immune abnormalities could be found in the peripheral immune compartment.

The periphery assumes an extremely important role in the study of MS. In remission phase is establish an equilibrium between CNS and systemic circulation. In this chapter we have attempted to contribute to highlight the more relevant data regarding circulating cell subsets that could potentially be considered as peripheral biomarkers in RRMS patients treated with IFN-β.

Some circulating immune cells assume differences between the remission and relapse phases of RRMS. These differences may be used as disease activity biomarkers to measure inflammatory and/or neurodegenerative components of disease and helpful to discriminate between phases of RRMS.

Technological advances of flow cytometry have greatly increased the strength of analysis achievable at the single-cell level. These developments can be applied to understand more clearly the immunopathology of MS and the identification of consistent, safe and reproducible biomarkers in the periphery.
