Abstract
Interleukin-12 (IL-12) stimulates natural killer (NK) and T cell production of interferon gamma (IFN-γ), but adverse events from NK cell activation have limited its clinical use. This study shows the impact of half-life-extended, full (IL-12Fc) and partial (IL-12 3x AlaFc) IL-12 agonists on the immune system. In naive mice, serial treatment with IL-12Fc induces systemic IFN-γ, multi-organ pathology, and alterations in myelopoiesis. IL-12 Fc stimulates NK cell production of IFN-γ but also activates CD4+, CD8+ T, and NKT cells. IL-12 Fc's ability to enhance the production of IFN-γ facilitates myelopoiesis, but IFN-γ is not required for the development of systemic toxicity. In contrast, IL-12 3x Ala Fc avoids overt disease, activates CD4+ and CD8+ T cells, and induces myelopoiesis. These differential activities were harnessed to enhance resistance to infection, indicating that a threshold of IL-12 signaling is tolerated under steady-state conditions and that fine-tuning IL-12 agonism can bolster resistance without triggering pathology.