NK cell-derived GM-CSF is critical for enhancing pathological arthritis

GM-CSF is involved in immune complex (IC)-mediated arthritis. However, little is known about what is the cellular source of GM-CSF and how it is regulated during IC-mediated inflammation. Using novel GM-CSF reporter mice, we show that NK cells produce GM-CSF during an IC-mediated model of inflammatory arthritis. NK cells promoted STIA in a GM-CSF-dependent manner, as deletion of NK cells and selective removal of GM-CSF production by NK cells abrogated disease. Furthermore, we show that myeloid cell activation by GM-CSF is restrained by induction of JAK/STAT checkpoint inhibitor cytokine-inducible SH2-containing protein, CIS. Myeloid cells from CIS-deficient mice had exaggerated responses to GM-CSF, and these mice develop exacerbated STIA. Our data suggest that tissue NK cells may amplify joint inflammation in arthritis via GM-CSF production and thus represent a novel target in IC-mediated pathology. Endogenous CIS provides a key brake on signaling through the GM-CSF receptor and strategies that boost its function may provide an alternative anti-inflammatory approach.