Given that additional TLR2 deficiency did not affect the microbiota of IL1rn−/− mice to a major extent (Fig. 1), we speculate that severe arthritis in IL1rn−/−Tlr2−/− mice is due to the altered host immune response, specifically reduced function of Treg cells [12], rather than alteration in the microbiome. This evidence concerns the gene IL1RN and Arthritis.