In addition to the role of mature IL-33 in the progression of RA (14,16), the nuclear localization of pro-IL-33 in IL-1β/TNF-α stimulated cells may point to a regulatory function inside the cells, as it has been described for the other IL-1 family members IL-1α and IL-1F7b (17,18). This evidence concerns the gene IL1A and rheumatoid arthritis.