Tropism and Innate Host Responses of the 2009 Pandemic H1N1 Influenza Virus in ex Vivo and in Vitro Cultures of Human Conjunctiva and Respiratory Tract

Abstract

The novel pandemic influenza H1N1 (H1N1pdm) virus of swine origin causes mild disease but occasionally leads to acute respiratory distress syndrome and death. It is important to understand the pathogenesis of this new disease in humans. We compared the virus tropism and host-responses elicited by pandemic H1N1pdm and seasonal H1N1 influenza viruses in ex vivo cultures of human conjunctiva, nasopharynx, bronchus, and lung, as well as in vitro cultures of human nasopharyngeal, bronchial, and alveolar epithelial cells. We found comparable replication and host-responses in seasonal and pandemic H1N1 viruses. However, pandemic H1N1pdm virus differs from seasonal H1N1 influenza virus in its ability to replicate in human conjunctiva, suggesting subtle differences in its receptor-binding profile and highlighting the potential role of the conjunctiva as an additional route of infection with H1N1pdm. A greater viral replication competence in bronchial epithelium at 33°C may also contribute to the slight increase in virulence of the pandemic influenza virus. In contrast with highly pathogenic influenza H5N1 virus, pandemic H1N1pdm does not differ from seasonal influenza virus in its intrinsic capacity for cytokine dysregulation. Collectively, these results suggest that pandemic H1N1pdm virus differs in modest but subtle ways from seasonal H1N1 virus in its intrinsic virulence for humans, which is in accord with the epidemiology of the pandemic to date. These findings are therefore relevant for understanding transmission and therapy.

Pandemic H1N1 Influenza A Viruses Are Resistant to the Antiviral Activities of Innate Immune Proteins of the Collectin and Pentraxin Superfamilies

“…Of interest, a number of studies have established that seasonal and pandemic H1N1 viruses elicit similar innate responses from human airway cells. Seasonal and pandemic H1N1 viruses were both poor in their ability to induce expression of antiviral and inflammatory cytokine genes from human dendritic cells and macrophages (45), and did not differ in ability to induce proinflammatory cytokines from human pneumocytes and bronchiolar epithelial cells (46). Recognition of sialylated residues on NKp46 by the HA of seasonal or pandemic H1N1 viruses also induced NK cell-mediated killing of virusinfected target cells (47).…”

“…Initial studies demonstrated preferential binding of A(H1N1) pdm viruses to a2,6-linked sialic acids (11) although subsequent glycan array data indicate significant binding to both a2,6-linked and a2,3-linked sialic acids, unlike seasonal H1N1 viruses that showed a distinct preference for a2,6-linked sialic acids (48). Seasonal H1N1, H3N2, and A(H1N1) pdm viruses replicated to comparable levels in ex vivo cultures of human nasopharynx and lung tissues, but human conjunctiva showed preferential susceptibility to infection by A(H1N1) pdm (46), consistent with subtle differences in receptor specificity that could potentially affect pathogenesis in humans.…”

Early host response and immune signaling to 2009 pandemic influenza A (H1N1) viruses in primary cell culture models.

“…Currently there are mixed conclusions reported regarding what cell type is preferred by seasonal IAV with data supporting binding to ciliated and/or non-ciliated (goblet) cells [61,66]. Seasonal and H1N1pdm IAVs enter and replicate efficiently in ciliated cells that line the epithelial cell layer in the large and small airways of the respiratory tract, while H5N1 enters and replicates more efficiently in non-ciliated cells (type II pneumocytes) within the small lower airways ( Figure 3B) [74,75,[83][84][85][86][87].…”

“…Moreover a large percentage of children without pre-existing comorbidities presented with upper and lower respiratory tract involvement. This led some researchers in the influenza field to ask whether the HA had a broader specificity for human receptors since the HA of this virus had an avian origin [66, [74][75][76]. One avian signature of the HA is at the G position 222 in the HA [77,78].…”

“…Hence, the spatial distribution and concentration of potential receptors associated within different areas of the respiratory tract and/or different cell types are integral in the study of IAV infection and disease [75,[88][89][90][91].…”