Discordant Interleukin-27 (IL-27) Subunit Transcription in Human Sepsis Exposes a Molecular-Attribution Gap

Background/Objectives: Interleukin-27 (IL-27) is an obligate EBI3–p28 heterodimer, yet sepsis studies commonly measure and target the axis as a single entity. We tested whether both subunit transcripts are coordinately induced in septic monocytes and whether the axis has functional consequences. Methods: We integrated 272,993 whole-blood single-cell transcriptomes from 39 individuals, six additional single-cell cohorts and eight bulk cohorts, with two human macrophage datasets, a tolerant-like THP-1 model and caecal ligation and puncture in male C57BL/6 mice. Results: Across three cohorts (166 donor records), EBI3 ranked 137th of 13,872 genes whereas IL-27 ranked 9413th. Against post-cardiac-surgery controls, detection odds ratios (ORs) were 11.0 for EBI3 and 0.78 for IL-27 (ratio 13.3). Thirteen of 7164 septic monocytes carried both transcripts, matching the chance expectation (co-detection odds ratio 0.91, 95% CI 0.48–1.75) against 5.6–346.7 for concordantly transcribed benchmark complexes; the receiver-side module estimate was β = −0.0151. The imbalance was reproduced in human macrophages. In tolerant-like THP-1 cells, IL-27-associated immunoreactivity retained 79.3% of its acute value versus 14.7% for tumour necrosis factor (TNF). p28-directed intervention increased murine 120 h survival from 10% to 45%. Conclusions: Human sepsis shows marked IL-27 subunit discordance across producer and receiver compartments while retaining functional sensitivity of the p28-associated axis, defining a molecular-attribution gap between pathway activity and intact heterodimeric IL-27.