IL-27 and IL-35 could serve as biomarkers of disease severity in neuromyelitis optica spectrum disorders (NMOSDs), new research suggests. The authors reported that in 45 patients with NMOSD, decreased levels of these cytokines in the serum correlated with increased disease severity; moreover, low levels of IL-27 and IL-35 correlated with spinal cord lesion length and higher annual relapse rate, respectively. The findings implicate IL-27 and IL-35 in NMOSD pathogenesis, and these cytokines might also have value as therapeutic molecules in NMOSD.