Serum macrophage migration inhibitory factor levels predict brain atrophy in people with primary progressive multiple sclerosis

Background: Macrophage migration inhibitory factor (MIF) is a cytokine linked to multiple sclerosis (MS) progression that is thought to be inhibited by ibudilast. SPRINT-MS was a phase 2 placebo-controlled trial of ibudilast in progressive multiple sclerosis (PMS). Objective: To determine whether baseline MIF levels predict imaging outcomes and assess the effects of ibudilast on serum and cerebrospinal fluid (CSF) MIF levels in people with PMS treated with ibudilast. Methods: Participants in the SPRINT-MS trial were treated with either ibudilast or placebo and underwent brain magnetic resonance imaging (MRI) every 24 weeks over a duration of 96 weeks. MIF was measured in serum and CSF. Results: MIF levels were compared with imaging outcomes in 223 participants from the SPRINT-MS study. In the primary progressive multiple sclerosis (PPMS) cohort, males had higher serum (p < 0.001) and CSF (p = 0.01) MIF levels, as compared with females. Higher baseline serum MIF levels in PPMS were associated with faster brain atrophy (beta = −0.113%, 95% confidence interval (CI): −0.204% to −0.021%; p = 0.016). These findings were not observed in secondary progressive multiple sclerosis (SPMS). Ibudilast did not affect either serum or CSF MIF levels. Conclusions: Serum MIF levels were associated with male sex and predicted brain atrophy in PPMS, but not SPMS. Ibudilast did not demonstrate an effect on MIF levels, as compared with placebo, although we cannot exclude a functional effect.