Data for Fig 5F.

Red blood cell production is regulated by erythropoietin (Epo), maintaining tissue oxygen tension in the steady state and in response to stress. To date, only a handful of factors other than Epo are known to stimulate erythropoiesis, limiting therapeutic options. We recently found that IL-17, a pleiotropic pro-inflammatory cytokine, interacts synergistically with Epo to increase formation of erythroid colonies in vitro. Here, we administered IL-17 to mice to determine whether it accelerates erythropoiesis in vivo. We found that while IL-17 alone had little effect on erythroid and other hematopoietic lineages, combined treatment with both IL-17 and Epo generated a specific and strong synergistic response in erythroid progenitors that significantly increased erythropoietic rate. IL-17 administration also accelerated the erythropoietic response of mice to hypoxia. Single-cell transcriptomic analysis showed that IL-17 acts by sensitizing erythroid progenitors to Epo, rather than through a distinct transcriptional response. Using a dynamical model, we propose that this mechanism optimizes conflicting requirements in the regulation of erythropoiesis, balancing the need for low-cost maintenance of the steady state, with a sufficiently fast stress response. Further, our findings suggest a potentially broadly applicable mechanism whereby pleiotropic cytokines are able to exert lineage-specific effects when their actions are dependent on synergism with lineage-specific factors.