IRF3 and susceptibility to pneumonia measurement: Furthermore, administration of vitamin C to patients with pneumonia induced by influenza virus (H1N1) showed a markedly reduced expression level of susceptibility genes, including interferon regulatory factor 3 (IRF3), mitochondrial antiviral signalling (MAVS), with an increase in nuclear factor kappa light chain enhancer of activated B cells (NF-κB) (Cai et al. 2015).