SFTPD and influenza: A study comparing humoral mediator profiles in patients with influenza and COVID-19 demonstrated that the expression levels of interleukin-2 (IL-2), a proliferation-inducing ligand (APRIL), soluble tumor necrosis factor receptors 1 and 2 (sTNF-R1 and sTNF-R2), surfactant protein D, and chemokine (C-X-C motif) ligand 17 (CXCL17) were characteristically elevated in influenza.