CCL4 and cancer: In terms of cytokine production, the analysis results based on TIMER2.0 database suggested that TREM2 expression was positively associated with the levels of cytokines which promoted the development of cancers and triggered the formation of immunosuppressive TME including IL-6, IL-10, TGF-β1, CCL2, CCL3, CCL4, CCL5, CCL7, CCL8, CXCL2 and CXCL9, while negatively correlated with anti-tumor cytokine IL-13 production (Fig. S2).