Two T helper (Th) cell subsets trigger the same multiple sclerosis (MS)-like symptoms but varying disease pathologies, say Kroenke et al. (page 1535).

Inflammatory Th1 cells and Th17 cells can both drive experimental autoimmune encephalitis (EAE)—the mouse equivalent of MS. The authors found that mice injected with either cell type developed paralysis with the same speed and severity, which might suggest that both cell types trigger the same pathology.

A closer look at the damage, however, told a different tale. Mice injected with Th1 cells developed macrophage-filled lesions in the central nervous system (CNS)—a sign of conventional MS. But mice injected with Th17 cells developed lesions filled with neutrophils, most likely in response to neutrophil-attracting chemokines that were produced in the CNS.

As neutrophils are highly adept at breaking down the blood–brain barrier, their presence might explain why Th17-induced lesions, unlike Th1-induced lesions, reached deep into CNS tissues. Th17 cells caused severe inflammation in the optic nerves and in sections of the spinal cord—typical of rare variants of MS, which do not respond to conventional treatment.

If similar differences are found in the pathology of MS, patients may benefit from therapies tailored to specifically inhibit the type of Th cell that is to blame.