The development of clinical activity in relapsing-remitting MS is associated with a decrease of FasL mRNA and an increase of Fas mRNA in peripheral blood.

In this longitudinal study, we examined the expression of Fas, FasL, CCR3, CCR5 and CXCR3 mRNA in peripheral blood mononuclear cells (PBMCs) of secondary progressive (SP) and relapsing-remitting (RR) multiple sclerosis (MS) patients. In RR patients, FasL, CCR3 and CCR5 mRNA levels were increased prior to the exacerbations, but these decreased during clinical activity, while mRNA levels of Fas increased. SP patients have increased the levels of Fas and FasL mRNA; the latter was particularly increased during lesional activity. Our data support the hypothesis that changes in Fas and FasL mRNA related to clinical activity are due to the migration of inflammatory cells to the central nervous system (CNS).