GM-CSF secreting Th cells are discreetly regulated during neuroinflammation. Fate-mapping of GM-CSF cytokine secretion identifies a discrete subset of T helper cells that drive neuroinflammation

Pathogenic lymphocytes initiate the development of chronic inflammatory diseases. The cytokine GM-CSF (Csf2) is a key communicator between pathogenic lymphocytes and tissue-invading inflammatory phagocytes. However, the molecular properties of GM-CSF-producing cells and the mode of Csf2 regulation in vivo remain unclear. To systematically study and manipulate GM-CSF+ cells and their progeny in vivo, we generated a fate-map and reporter of GM-CSF expression mouse strain (FROG). We mapped the phenotypic and functional profile of auto-aggressive T helper (Th) cells during neuroinflammation and identified the signature and pathogenic memory of a discrete encephalitogenic Th subset. These cells required interleukin-23 receptor (IL-23R) and IL-1R, but not IL-6R signalling for their maintenance and pathogenicity. Specific ablation of this subset interrupted the inflammatory cascade, despite the unperturbed tissue accumulation of other Th subsets (e.g. Th1, Th17), highlighting that GM-CSF expression not only marks pathogenic Th cells, but that this subset mediates immunopathology and tissue destruction.