In addition to the known caveats of modeling human arthritis in mice (19, 64), the direct translatability of our findings in SKG arthritis might be limited by differences in the expression patterns of GPR15 between human and mouse immune cells (in humans, GPR15 is mainly found on effector cells and to lesser extent on Tregs, refs. 61, 65). The gene discussed is GPR15; the disease is Arthritis.