CD274 and melanoma: PM2.5-pretreated BMDMs exhibited an immunosuppressive programmed cell death ligand 1 (PD-L1)+/arginase 1 (Arg1)+ phenotype, and their conditioned media significantly promoted proliferation, migration, and colony formation of Lewis lung carcinoma cells (LLC) and B16 melanoma cells (B16) (P<0.05).