Background <p>Ischemia-induced inflammation is the primary pathological mechanism underlying cardiac tissue injury caused by myocardial infarction (MI). <i>Trichinella spiralis</i> cystatin (<i>Ts</i>-Cys) has been shown to regulate macrophage polarization and alleviate various inflammatory and immune-related diseases. Programmed cell death-1 (PD-1) is a crucial checkpoint receptor molecule and highly involved in maintaining immune tolerance. In this study, our aims were to investigate whether recombinant <i>Ts</i>-Cys protein (r<i>Ts</i>-Cys) could be used to treat MI with recruited macrophage-dominant myocardial inflammation and whether PD-1 is involved in the immunomodulation of <i>Ts</i>-Cys in inflammatory diseases.</p> Methods <p>MI models were established in wild-type (WT) and PD-1 knockout (PD-1^−/−) mice, followed by the intraperitoneal injection of r<i>Ts</i>-Cys. The survival rates of mice were observed for 28&#xa0;days post-surgery and treatment. Cardiac function was assessed by echocardiography. Histopathological evaluation of heart tissue affected by infarction was conducted to examine local inflammatory cell infiltration and cardiac tissue damage. Real-time quantitative PCR was used to detect messenger RNA expression levels of vascular endothelial growth factor (VEGF) and the macrophage surface markers inducible nitric oxide synthase and arginase-1 in the MI area. Serological levels of cytokines, including tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), interleukin-10 (IL-10) and transforming growth factor-beta (TGF-β), were measured using an enzyme-linked immunosorbent assay. Bone marrow-derived macrophages from WT and PD-1^−/− mice were used to assess the effects of r<i>Ts</i>-Cys on macrophage polarization in vitro.</p> Results <p>In WT mice, r<i>Ts</i>-Cys treatment significantly improved the 28-day survival rate and cardiac function, reduced local inflammatory cell infiltration and cardiac pathological damage and increased VEGF expression levels of MI mice. The therapeutic effect of r<i>Ts</i>-Cys was associated with macrophage polarization from the pro-inflammatory M1 phenotype to the regulatory M2 phenotype with reduced levels of inflammatory cytokines (TNF-α and IL-6) and increased levels of regulatory cytokines (IL-10 and TGF-β), as determined by both in vivo and in vitro tests. However, this therapeutic effect of r<i>Ts</i>-Cys on MI was significantly reduced in PD-1^−/− mice, as reflected by the higher level of M1 macrophages, elevated levels of inflammatory cytokines and decreased levels of regulatory cytokines.</p> Conclusions <p>r<i>Ts</i>-Cys promotes M2-type polarization of macrophages through the PD-1 pathway to alleviate MI in mice and is, therefore, a potential drug for the treatment of MI and other inflammation-related diseases with involvement of the PD-1 checkpoint molecule.</p> Graphical Abstract <p></p>