Exploring Functionally Enhanced BLP‐Trained Macrophage Subpopulations in <i>S. Aureus</i> Infection: Underlying Mechanisms and Therapeutic Significance

Tolerance to bacterial lipoprotein (BLP) is an evolved protective mechanism characterized by an enhanced resistance of BLP-trained macrophages to microbial infection. However, the underlying mechanisms are not fully understood, and their potential for translational clinical application needs further evaluation. In the present study, through single-cell RNA sequencing (scRNA-seq), transcriptomic profiles in both naïve and BLP-trained bone marrow-derived macrophages (BMDMs) during Staphylococcus aureus infection are analyzed, and 13 distinct BMDM subpopulations are identified. Notably, BLP-trained tolerance initiates the emergence of two novel BMDM subpopulations, C5 and C7, characterized by increased antibacterial gene expression and enhanced anti-inflammatory and antioxidative stress abilities. Moreover, BLP-trained BMDMs demonstrate activation of the NRF2 signaling pathway, thereby augmenting an antioxidative stress response and mitigating oxidative stress-induced cell damage and ferroptosis, while undergoing metabolic reprogramming characterized by enhanced glycolysis and oxidative phosphorylation pathways, together with increased anti-inflammatory metabolites. Critically, in vivo adoptive transfer of BLP-trained BMDMs protects mice against sepsis-associated lethality by attenuating systemic inflammatory response, accelerating bacterial clearance, and alleviating organ damage. Collectively, the present study presents a single-cell atlas of murine BMDMs at rest and under S. aureus infection following BLP training, which reveals novel mechanisms of BLP training-altered macrophage immunity and identifies macrophage subpopulations responsible for an enhanced resistance to infection, thus offering new preventive and therapeutic strategies for sepsis.