TGF-β regulated Tim-3 sustains macrophage phagocytic function and confers protection in Plasmodium yoelii NSM-infected mice.

BACKGROUND: T-cell immunoglobulin and mucin domain 3 (Tim-3) is a critical immune checkpoint, yet its role in regulating macrophage function during malaria infection remains poorly understood. METHODS: We established a Plasmodium yoelii NSM murine model, in vitro co-culture systems, and comprehensive techniques including scRNA-seq, flow cytometry, and functional assays to investigate Tim-3 expression on splenic macrophages and its immunoregulatory impact. RESULTS: We observed a significant infection-induced downregulation of Tim-3 on splenic macrophages. Transcriptomic profiling revealed that Tim-3(+) macrophages exhibited enhanced antigen presentation and a proinflammatory phenotype characterized by elevated reactive oxygen species (ROS) and proinflammatory cytokine production. Blockade of Tim-3 in vivo exacerbated disease severity, increased parasitemia, and impaired macrophage phagocytic capacity, without directly affecting T-cell responses. Mechanistically, we identified transforming growth factor-beta (TGF-β) as a key upstream regulator of Tim-3 expression, as TGF-β signaling was suppressed during infection, and its stimulation or inhibition correspondingly upregulated or downregulated Tim-3. Furthermore, TGF-β-induced Tim-3 upregulation potentiated macrophage phagocytosis of infected red blood cells (iRBCs) and conferred protection against iRBC-induced cell death. CONCLUSIONS: Our results reveal a novel protective TGF-β-Tim-3 axis that maintains the phagocytic function of macrophages and immune homeostasis in Plasmodium yoelii NSM infection. These findings highlight Tim-3 on macrophages as a potential therapeutic target for modulating host defense against malaria infection.