In mouse studies of the closely related SARS-CoV, it was found that products of C3 activation such as C3a, C3b, and iC3b were detectable in the lungs a single day after infection, and that C3−/− mice had less severe lung injury, had fewer neutrophils and inflammatory monocytes, and had reduced cytokine and chemokine levels. This evidence concerns the gene C3 and infection.