CCL2 and infection: Using cells only treated with IL-33 or cells only infected with HTNV as controls, the mRNA expression of IL-1β, IL-6, IL-8, CCL2, CCL20, CXCL1, CXCL2, and CX3CL1 was significantly induced in HUVECs prior to infection with HTNV (MOI = 1) for 48 h and then exposed to IL-33 (20 ng/ml) for 6 h (Fig. 3).