ARG1 and relapsing-remitting multiple sclerosis: In the other, when human MDSCs were expanded by glucocorticoid (GlC) treatment during relapse [107], RRMS patients produced a higher proportion of PMN-MDSCs after GlC infusion that translated into higher serum Arg-1 levels, weaker expression of the β subunit of the human GlC receptor, and higher activating transcription factor 3 serum levels, which is implicated in important signaling pathways that mediate PMN-MDSC accumulation.