Aoife O’Farrell, Zijian Niu, Jingxin Li, Laura C Van Eyndhoven, Kavitha Sarma, Arjun Raj. Human macrophages encode stimulus-specific information of prior exposures through trained immunity. Cell Syst. 2026 Jun 19:101647. doi: 10.1016/j.cels.2026.101647. Epub ahead of print. PMID: 42320478.

Abstract

Trained immunity (a form of innate immune memory) is defined in part by heightened responses to pathogen restimulation and can be generated by many different stimuli. However, both the quantitative differences in trained states generated by different stimuli and the downstream consequences of those differences remain unclear. Here, we used primary human monocyte-derived macrophages to demonstrate phenotypic and molecular stimulus specificity of trained immunity 6 days after initial exposure. Quantification of cytokine production with single-molecule RNA imaging revealed stimulus-specific patterns of response to restimulation, with trained cells showing stronger responses to secondary stimuli more similar to their initial stimulation. Differential licensing of inflammatory transcription factors was associated with encoding of specificities in chromatin 6 days after training, while memory of some, but not all, training stimuli was lost by 11 days post-training in vitro. Overall, our findings demonstrate that different training stimuli can impart specific memories that generate distinct training phenotypes.