Steroid hormone ouabain cooperates with Na+,K+-ATPase to improve innate immunity against bacterial infections through a non-classic training mechanism regulated by mRNA reprogramming.

Epigenetic reprogramming underpins trained immunity (TRIM). However, the importance of mRNA reprogramming in TRIM remains unknown. Here, we discovered, for the first time, that the steroid hormone ouabain creates a significant training effect on peripheral innate immune cells (IICs), leading to functional enhancement of IICs against bacterial infections. However, unlike conventional training mechanisms, ouabain primarily relies on an integrated posttranscriptional RNA regulon complex (IPRRC) to establish immune memory and reprogram cytokine expression, with lncRNA-CYTOR playing a critical role in this process. Moreover, to enhance training effects while reducing lactate production, ouabain promotes a rapid degradation of the Na+,K+-ATPase receptor. Pathologically, endogenous ouabain is downregulated in sepsis-induced immunoparalysis in vivo, correlating with impaired innate immunity. Exogenous ouabain rescue significantly reverses this impairment, and its effect is superior to β-glucan, even when used at one percent of β-glucan dosage. Notably, posttranscriptional RNA regulons are also critically involved in β-glucan's training effects. Overall, mRNA reprogramming emerges as a new mechanism for TRIM; steroid hormone ouabain is a novel innate immunity regulator.