The Battle Between Influenza and the Innate Immune Response in the Human Respiratory Tract

Nicholls, John M

It is therefore important to understand whether influenza virus targets mainly type 1 or type 2 epithelial cells. Van Riel and colleagues have performed virus binding assays and demonstrated that H5N1 bound to type 2 cells within the lung with the type 1 cells binding seasonal H1N1 [50] . This has been corroborated by ex vivo infections of lung tissues that demonstrated viral egress from type 2 rather than type 1 cells [51] . This implies that the destruction of type 1 cells leading to diffuse alveolar damage might not be due to a direct viral cytopathic effect but may be secondary to a cytokine mediated destruction. Analysis of this effect in the laboratory is challenging as keeping isolated type 2 cells in their native state is difficult as they rapidly differentiate into type 1-like cells [44] . Though many investigators have used the A549 cells as "representing" the lung epithelium, this cell line is derived from a type 2 pneumoctye tumour and does not faithfully represent their non-neoplastic counterpart (e.g lack surfactant production and require trypsin to be added for efficient virus replication).