In order to confirm that indeed the interaction between DC-SIGN and glycans on HA are at the basis of the observed increased infection percentages in DC-SIGN expressing cells, we used genetically modified influenza A/H1N1 viruses, A/Netherlands/26/07 and A/Netherlands/602/09 (H1N1pdm09), of which N-linked glycosylation sites were reciprocally exchanged to produce viruses that gained or lost one or more putative N-linked glycosylation sites. Here, CD209 is linked to infection.