The impact of harvest time on the HA N-glycosylation pattern of MDCK cell-derived IVA-Uruguay is shown in figure 1B . Virus harvested at either 24 hpi or 72 hpi exhibited the 25 different MDCK cell-specific peaks between 160 bp and 400 bp. At 72 hpi one additional, but very low abundant peak was detected (numbered 23). Overall, differences in relative structure abundance were rather small with a maximal difference of 1.7 % (table 1) . This indicates that HA of virus particles released in the supernatant is rather stable over the time window relevant for influenza virus production [5, 6] ]. However, there are minor variations in RPH from passage to passage during adaptation and between harvesting time points. Possible explanations are varying ratios either of completely/incompletely processed or of intact/ degraded N-glycan structures or a combination of both. In 2009, Schwarzer et al. [7] characterized the MDCK cell-derived HA N-glycosylation pattern of a H3N2 influenza virus subtype as a mixture of complex N-glycan structures with terminal αand β-galactose and high mannose type structures. In contrast, the Vero cellderived HA was characterized by complex N-glycans with exclusively terminal β-galactose and structures of the high mannose type. For final evaluation of the results presented here, determination of the N-glycan structure of all peaks would be required.