Identifying specific roles for individual cytokines is complicated by the observation that they share common functional subunits. Interleukin-12 (IL-12) is a heterodimer of p35 and p40 subunits, and is thought to be important in T-cell-dependent immunity and inflammation. In the February 13
Cua et al. used knockout mice and cytokine replacement studies to address the role of the p19, p35 or p40 subunits in experimental autoimmune encephalomyelitis (EAE) — an inflammatory disease model. IL-23, but not IL-12, was essential for the development of EAE. IL-23 directly activated macrophages in vivo, inducing cytokine expression and late-stage inflammation.