Avian-Type Receptor-Binding Ability Can Increase Influenza Virus Pathogenicity in Macaques

Abstract

The first influenza pandemic of the 21st century was caused by novel H1N1 viruses that emerged in early 2009. An Asp-to-Gly change at position 222 of the receptor-binding protein hemagglutinin (HA) correlates with more-severe infections in humans. The amino acid at position 222 of HA contributes to receptor-binding specificity with Asp (typically found in human influenza viruses) and Gly (typically found in avian and classic H1N1 swine influenza viruses), conferring binding to human-and avian-type receptors, respectively. Here, we asked whether binding to avian-type receptors enhances influenza virus pathogenicity. We tested two 2009 pandemic H1N1 viruses possessing HA-222G (isolated from severe cases) and two viruses that possessed HA-222D. In glycan arrays, viruses possessing HA-222D preferentially bound to human-type receptors, while those encoding HA-222G bound to both avian-and human-type receptors. This difference in receptor binding correlated with efficient infection of viruses possessing HA-222G, compared to those possessing HA-222D, in human lung tissue, including alveolar type II pneumocytes, which express avian-type receptors. In a nonhuman primate model, infection with one of the viruses possessing HA-222G caused lung damage more severe than did infection with a virus encoding HA-222D, although these pathological differences were not observed for the other virus pair with either HA-222G or HA-222D. These data demonstrate that the acquisition of avian-type receptor-binding specificity may result in more-efficient infection of human alveolar type II pneumocytes and thus more-severe lung damage. Collectively, these findings suggest a new mechanism by which influenza viruses may become more pathogenic in mammals, including humans.In the early spring of 2009, the human population was confronted by a novel swine origin H1N1 influenza virus that caused the first influenza pandemic of the 21st century. In most cases, human infections with this virus appeared to be mild; however, many severe and fatal cases were reported in individuals who had no other underlying health issues (3). Yet, the virulence factors of the 2009 pandemic H1N1 virus, if any, remain poorly understood.Host range and pathogenicity of influenza viruses are determined by both viral and host factors. The receptor-binding specificity of the hemagglutinin (HA) protein plays a role in host range restriction (18). In general, human influenza viruses preferentially bind to sialic acid linked to galactose by an ␣2,6 linkage (SA␣2,6Gal), which is prevalent in human airway epithelium, whereas avian influenza viruses have higher affinity for SA␣2,3Gal, the major sialyloligosaccharide species in duck intestine, where aquatic bird influenza viruses replicate (24).

Characterization In Vitro and In Vivo of Pandemic (H1N1) 2009 Influenza Viruses Isolated from Patients

“…6). In agreement with previous studies (5,19,35,38), these results suggest that an Asp-to-Gly amino acid change at position 222 of the HA of Norway3487 virus confers the ability to recognize both avian-type and human-type receptors.…”

“…The more pathogenic Norway3487 virus has the Asp-to-Gly change at position 222 of its HA, conferring avian-type receptor-binding specificity. Thus, this change may result in more efficient infection of human alveolar type II pneumocytes, which express avian-type receptors, reducing the availability of progenitor cells for essential lung functions and thus leading to severe pulmonary impairment, diffuse alveolar damage, and respiratory distress, culminating in the increased pathogenicity in nonhuman primates described previously (35,37). Moreover, we found that PB2 derived from Norway3487 virus contributed to higher polymerase activity, possibly leading to more efficient viral replication in vitro and in vivo.…”

“…Norway3487 and Norway3568 differ by only 10 amino acids (4 in the polymerase subunit PB2 and 1 in the polymerase subunit PB1, 2 in the interferon-antagonist protein NS1, 1 in NA, and 2 in HA [ Table 2]). However, none of the amino acid changes known to affect virulence were found in PB2, PB1-F2, HA, or NS1 (6, 8, 11, 14, 16, 18, 24, 29, 33), except for an Asp-to-Gly amino acid change at position 222 of the HA of Norway3487 virus, which has recently been identified as a potential virulence marker of A(H1N1)pdm09 viruses (35,37).…”

“…examine the receptor-binding specificity of Norway3487 and Norway3568 viruses, we conducted glycan microarrays as described elsewhere (35). As expected, Norway3568 virus, which possesses HA222-Asp (5), efficiently bound to ␣2,6Gal-sialylated glycans (human-type receptor), whereas Norway3487 virus, which possesses HA222-Gly, bound to multiple ␣2,3Gal-sialylated glycans (avian-type receptor) as well as to ␣2,6Gal-sialylated glycans (Fig.…”

Virulence and transmissibility of H1N2 influenza virus in ferrets imply the continuing threat of triple-reassortant swine viruses

“…Notably, severe viral pneumonia attributed to efficient virus attachment to α2,3-sialic acid glycoconjugates deep in the lungs have been observed in H5N1 (25) and HA 225G variants of the pH1N1 (5,(26)(27)(28)(29)(30) virus infections. Moreover, it has been demonstrated that avian-type receptor-binding ability because of HA 225G increased pathogenicity of the pH1N1 2009 virus in nonhuman primates (31).…”