ST6GAL1 and infection: Of note was that sialyl transferases adding sialic acid α2,3-linked to Gal were generally weakly upregulated in response to infection for most viruses (ST3GAL2 in spleen, ST3GAL4 in lung, ST3GAL5 in spleen) whereas ST6GAL1 encoding a sialyl transferase adding sialic acid α2,6-linked was weakly downregulated in all chicken tissues for most viruses, except H3N8 and H4N6.