CCL2 and susceptibility to pneumonia measurement: These experimental data indicate that similar to the above-described IAV-induced pneumonia induction, the production of type I IFNs in infected lung tissue can result in excessive infiltration of monocytes and neutrophils and CCL2-mediated accumulation of monocyte-derived macrophages are at least partly responsible for the generation of tissue injury in SARS-CoV infection (Fig. 4).