By analyzing the position of glycosites and their conservative rates, we conclude that two types of glycosites appear in HAs: one with a high level of conservation in all HA subtypes and another with various conservative rates in different HA subtypes. Two highly conserved glycosites are located near the HA0 cleavage site (e.g., the 27NNST in H1 or the 30NGT in H8) and the fusion peptide of the HA2 (e.g., the 498NGT in H1 or 500NGS in H5) respectively in all subtypes, and these two glycosites play necessary role in viral life cycle for protecting the HA0 cleavage sites and fusion peptide [34, 51] . In addition, another highly conserved glycosite appears at C-terminal part of the HA1 sequence, which is near the connection of the global and stalk domains, except in H7 and H15 sequences [52] . Three to ten characteristic glycosites were distinctive in each subtype. Their conservative rates were influenced by different internal evolution branches, ranked from 0.5% (e.g., 292NGS with 2.85% in H3) to 100% (e.g., 38NGT with 99.94% in H3), distributed mainly in the global domain. It is worth mentioning that some highly conserved glycosites were near to cysteines (Figure 1 ). Kozlov et al. hypothesized that ERp53, which is involved in the formation of disulfide bonds during the folding of nascent proteins, would form a complex with calreticulin/calnexin, which depends on precursor N-glycans [53] .