Background: Knee osteoarthritis (OA) is a prevalent, age-related form of arthritis, characterized by chronic inflammation. However, quantitative tools to assess inflammatory homeostasis are currently lacking. Thus, this study aimed to develop a tool for quantitatively evaluating inflammatory homeostasis in knee OA.

Methods: We developed the EntroInflame score, a quantitative algorithm integrating single sample gene set enrichment analysis (ssGSEA) scores and Shannon entropy of inflammation-associated genes from single-cell meniscus RNA-seq data (12 samples and 67,681 cells), to evaluate inflammatory homeostasis.

Results: Based on the algorithm, we identified a unique type of inflammation homeostatic cells (with EntroInflame score < 0.5) in meniscus tissue. Through molecular characterization analysis, we found that signaling pathways, such as the phosphoinositide 3 kinase-protein kinase B (PI3K-Akt), mitogen activated protein kinase (MAPK) and longevity-regulating pathway, are closely associated with the functions of inflammation homeostatic cells. In addition, the macrophage migration inhibitory factor-atypical chemokine receptor 3 (MIF-ACKR3) was pinpointed as a vital link between inflammation and non-inflammation homeostatic cells, suggesting its therapeutic potential. Furthermore, we utilized computational biology methods to predict compounds targeting inflammation homeostatic cells and constructed a scoring system based on literature evidence to assess their credibility.

Conclusions: In summary, our study establishes inflammatory homeostasis as a critical regulatory mechanism in OA and provides a framework for precision interventions. Currently, inflammation homeostatic cells are inferred through calculation. In the future, we will further verify them through in vivo and in vitro experiments.