NMU production by bone marrow-derived cells promotes autoantibody-mediated arthritis. Bone marrow chimeric mice were generated in the four indicated combinations. Following bone marrow engraftment, serum from K/BxN mice was injected on days 0 and 2 and the development of arthritis was assessed at the indicated timepoints. Data plotted are means ± SEM and represent one of two independent experiments with a total of eight mice per genotype. B6→B6 versus NMU-KO→B6, P = 0.006; B6→B6 versus NMU-KO→NMU-KO, P = 0.022; B6→NMU-KO versus NMU-KO→B6, P = 0.007; B6→NMU-KO versus NMU-KO→NMU-KO, P = 0.027. There was no statistical difference between the two groups in which B6 mice were donors (P = 0.999) or between the two groups in which NMU-KO mice were donors (P = 0.880) (repeated-measures analysis of variance followed by post-hoc Tukey's multiple comparison test). B6: C57BL/6; NMU: neuromedin U; SEM: standard error of the mean.