Most of the proteins — known as cytokines — in the interleukin 1 family are thought to spark inflammation while defending the body. Charles Dinarello at the University of Colorado Denver in Aurora and his colleagues show that one cytokine in the group instead dampens inflammation. The finding reveals the function of IL-37, which has been mysterious since it was discovered a decade ago.

The researchers first used RNA interference to turn off production of IL-37 in blood cells. Those cells showed an increased immune response when treated with molecules common to bacterial membranes to mimic infection. When they expressed the human form of IL-37 in transgenic mice, they found that it protected the animals against organ damage caused by severe infection, probably by reducing the production of pro-inflammatory cytokines.

Nature Immunol. doi:10.1038/ni.1944 (2010)