Single-Cell RNA Sequencing Reveals Dynamic Expression Patterns of MAIT Cells and Macrophage Subpopulations in Myocardial Injury Model

<h4>Background</h4>Mucosal-associated invariant T (MAIT) cells are innate-like T lymphocytes involved in immune surveillance and tissue homeostasis. Yet, their transcriptional dynamics and functional crosstalk with macrophages at the time of myocardial injury are incompletely defined.<h4>Methods</h4>We used two publicly available single-cell RNA sequencing (scRNA-seq) datasets from a murine ischemia-reperfusion myocardial injury model (GSM8252253 and GSM8252254). Following quality control and clustering, immune cell composition, cytokine expression patterns, and macrophage polarization states were systematically characterized. Concurrently, in vitro coculture experiments validated the MR1-dependent regulatory effects of 5-OP-RU-activated MAIT cells on macrophage cytokine expression.<h4>Results</h4>Single-cell analysis showed significant immune remodeling on Day 7 post-injury, with a relative expansion of B cells and depletion of macrophages compared to controls. UMAP-based feature mapping revealed that expression of Tnf was significantly restricted to myeloid compartments (especially monocytes), whereas Il10 exhibited a diffuse pattern across immune subsets. MAIT cells exhibited increased expression of signature genes such as ZBTB16 and KLRB1 consistent with activation-associated transcriptional reprogramming after damage. Macrophage populations exhibited heterogeneous polarization states, with limited TNF-α/IL-10 coexpression and overall low Il10 abundance in vivo. Functional validation showed that 5-OP-RU-activated MAIT cells significantly suppressed TNF-α while enhancing IL-10 expression in macrophages, and these effects were largely reversed by MR1 blockade.<h4>Conclusions</h4>Our findings reveal dynamic immune cell remodeling and transcriptional adaptation of MAIT cells during myocardial injury. The predominance of Tnf-driven myeloid signaling and the MR1-dependent anti-inflammatory modulation of macrophages by activated MAIT cells highlight a potential regulatory axis in cardiac inflammation. These results provide mechanistic insight into MAIT-macrophage interactions and suggest potential immunomodulatory targets for myocardial injury intervention.