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The biological paths of IL‐1 family members IL‐18 and IL‐33

Cytokines are key mediators of the immune system, and few have been more thoroughly studied than those of the IL‐1 family. IL‐1α and IL‐1β are the founding members and now celebrate 25 years since their cloning. In that time, IL‐1‐directed research has illuminated many aspects of cytokine biology and innate immunity. The family is now recognized to include 11 total members, including IL‐18 and IL‐33, which are the topic of this review. These two inflammatory cytokines are expressed broadly, and their actions influence a variety of physiologic responses involved in inflammation and immunity. The purpose of this article is not to provide an exhaustive review of IL‐18 and IL‐33 but rather, to summarize what is known about their key functions and to provide perspective on their similarities and differences.