Trained immunity is the process of long-term functional reprogramming (a de facto innate immune memory) of innate immune cells such as monocytes and macrophages after an exposure to pathogens, vaccines, or their ligands. The induction of trained immunity is mediated through epigenetic and metabolic mechanisms. Apart from exogenous stimuli, trained immunity can be induced by endogenous compounds such as oxidized LDL, urate, fumarate, but also cytokines including IL-1α and IL-1β. Here, we show that also recombinant IL-36γ, a pro-inflammatory cytokine of the IL-1-family, is able to induce trained immunity in primary human monocytes, demonstrated by higher cytokine responses and an increase in cellular metabolic pathways both regulated by epigenetic histone modifications. These effects could be inhibited by the IL-36 receptor antagonist as well as by IL-38, an anti-inflammatory cytokine of the IL-1 family which shares its main receptor with IL-36 (IL-1R6). Further, we demonstrated that trained immunity induced by IL-36γ is mediated by NF-κB and mTOR signaling. The inhibitory effect of IL-38 on IL-36γ-induced trained immunity was confirmed in experiments using bone marrow of IL-38KO and WT mice. These results indicate that exposure to IL-36γ results in long-term pro-inflammatory changes in monocytes which can be inhibited by IL-38. Recombinant IL-38 could therefore potentially be used as a therapeutic intervention for diseases characterized by exacerbated trained immunity.
Keywords: IL-36; IL-38; epigenetics; immunometabolism; innate immune memory.