In this observational study, investigators explore the molecular mechanisms responsible for the impaired regulation of immune cells in relapsing-remitting (RR) MS patients with depression. Investigators will compare the molecular and phenotypical profile of immune cells obtained from RRMS patients with clinical depression (n=50), matched MS patients who do not suffer from depression (n=50) as well as matched healthy controls (n=50) and matched patients with depression but without a comorbid neurological disorder (n=50).