CCL2 and infection: Quantitative PCR analysis revealed increased mRNA levels of proinflammatory cytokines and chemokines (Tnf, Il6, Il1b, Ccl2, Cxcl1, and Cccl2) in SARS-CoV-2-infected lungs compared with those in naïve lungs on days 2 and 5 post-infection (Fig. 2C and D).