Abdollahi-Roodsaz et al. (56) using the IL-1 receptor antagonist-deficient (IL1rn−/−) mice that spontaneously develop T-cell-mediated autoimmune arthritis showed that germ-free (GF) IL1rn−/− presented no signs of arthritis during 20 weeks of follow-up, whereas matched non-GF animals started to develop the disease from the age of 5 weeks. Here, IL1RN is linked to arthritic joint disease.