[Lewis tumor cell conditioned medium enhances immunosuppressive function of mouse myeloid-derived suppressor cells by...

Objective To investigate the effect of tumor microenvironment on the metabolism and function of myeloid-derived suppressor cells (MDSCs). Methods The spleen-derived MDSCs of lung cancer xenograft mice were isolated by immunomagnetic beads. After treated by Lewis tumor cell conditioned medium (TCCM) for 48 hours, real-time PCR was used to detect the mRNA levels of lactate dehydrogenase A (LDHA), glucose transporter-1 (GLUT1) and hypoxia-inducible factor 1α (HIF-1α). The hexokinase (HK) method was used to detect the concentration of glucose; the lactic acid test kit was used to detect the content of lactic acid which was the final production of glycolysis; and the 5, 6-carboxyfluorescein diacetate succinimiyl ester (CFSE) staining combined with flow cytometry was used to detect the immunosuppressive function of MDSCs on the proliferation of CD4⁺ T cells. Arginase kit was used to detect arginase 1 (ARG1) activity of MDSCs, and nitric oxide kit was used to detect the level of inducible nitric oxide synthase (iNOS). Results Compared with the untreated group, the mRNA levels of LDHA, GLUT1 and HIF-1α were up-regulated; the activity of ARG1 and the level of iNOS significantly increased; the immunosuppressive function of MDSCs on the proliferation of CD4⁺ T cells was significantly enhanced after the treatment of TCCM. Conclusion TCCM can activate the glycolytic pathway, up-regulate the immunosuppressive function on the proliferation of CD4⁺ T cells and the release of immunosuppressive effector molecule of MDSCs.