CCL20 and viral infectious disease: The inhibitory effect of APN on the Poly(I:C)-induced production of CCL2, CCL5, CCL20, CXCL1, and CXCL8 might explain why viral infections [and particularly infections by the H1N1 influenza virus (Salvator et al., 2011)] are particularly severe in obese patients since the concentrations of APN are abnormally low in obese individuals (Ouchi et al., 2011).