RBP4 and COVID-19: We found an increase in both RBP4 and TTR in the serum of COVID-19 patients (Table 2), consistent with the secretion of this complex into circulation [54]; apolipoprotein C-IV (APOC4), a lipid-binding protein critical for activating lipoprotein lipase [57]; and immunoglobulin kappa constant (IGKC), an immunoglobulin isotype involved in immune response pathways such as the Fc epsilon RI pathway and NFAT in immune response.