Low-Level Expression of the E1B 20-Kilodalton Protein by Adenovirus 14p1 Enhances Viral Immunopathogenesis

Abstract

Adenovirus 14p1 (Ad14p1) is an emergent variant of Ad serotype 14 (Ad14) that has caused increased severity of respiratory illnesses during globally distributed outbreaks, including cases of acute respiratory distress syndrome and death. We found that human cell infection with Ad14p1 results in markedly decreased expression of the E1B 20-kilodalton (20K) protein compared to that with infection with wild-type (wt) Ad14. This reduced Ad14p1 E1B 20K expression caused a loss-of-function phenotype of Ad-infected cell corpses that, in contrast to cells infected with wt Ad14, either failed to repress or increased NF-κB-dependent, proinflammatory cytokine responses of responder human alveolar macrophages. A small-animal model of Ad14-induced lung infection was used to test the translational relevance of these in vitro observations. Intratracheal infection of Syrian hamsters with Ad14p1 caused a marked, patchy bronchopneumonia, whereas hamster infection with wt Ad14 caused minimal peribronchial inflammation. These results suggest that this difference in E1B 20K gene expression during Ad14p1 infection and its modulating effect on the interactions between Ad14-infected cells and the host innate immune response could explain the increased immunopathogenic potential and associated increase in clinical illness in some people infected with the Ad14p1 outbreak strain. IMPORTANCE We previously reported that Ad-infected human cells exhibit E1B 19K-dependent repression of virally induced, NF-κB-dependent macrophage cytokine responses (J. R. Radke, F. Grigera, D. S. Ucker, and J. L. Cook, J Virol 88:2658–2669, 2014, http://dx.doi.org/10.1128/JVI.02372-13 ). The more virulent, emergent strain of Ad14, Ad14p1, causes increased cytopathology in vitro , which suggested a possible E1B 20K defect. Whether there is a linkage between these observations was unknown. We show that there is markedly reduced expression of E1B 20K in Ad14p1-infected human cells and that this causes an increased proinflammatory cytokine response of human alveolar macrophages and more severe inflammatory lung disease in infected hamsters. This is the first evidence of a clinical relevance of differential expression of the small Ad E1B gene product. The results suggest that there is a low, critical threshold of E1B 19/20K expression that is needed for viral replication and infection transmission but that a higher level of E1B 19/20K expression is required for the usual repression and control of the Ad-triggered host innate immune response.