In two previous representative studies reporting that IL-33 exacerbates inflammation in periodontitis, one was performed by intraperitoneal administration of recombinant murine IL-33 before and after oral infection with Porphyromonas gingivalis in WT mice, and then analyzed 2 weeks later52; and the other was induced periodontitis in the same way using Il1rl1–/– mice55. The gene discussed is IL1RL1; the disease is periodontitis.