C3 and influenza: In fact, transferrin, Hpx, and complement factor B and C3 have been identified by quantitative proteomics in a mouse model of influenza as potential markers of disease severity that can be clinically useful in humans (Kumar et al., 2014), and Serping1 and complement factor B have been identified as candidate nasopharyngeal protein biomarkers in acute respiratory virus infection (Burke et al., 2017).