Heterogeneous pathological outcomes after experimental pH1N1 influenza infection in ferrets correlate with viral replication and host immune responses in the lung

Abstract

The swine-origin pandemic (p) H1N1 influenza A virus causes mild upper-respiratory tract disease in most human patients. However, some patients developed severe lower-respiratory tract infections with fatal consequences, and the cause of these infections remain unknown. Recently, it has been suggested that different populations have different degrees of susceptibility to pH1N1 strains due to host genetic variations that are associated with inappropriate immune responses against viral genetic characteristics. Here, we tested whether the pathologic patterns of influenza strains that produce different disease outcomes in humans could be reproduced in a ferret model. Our results revealed that the severities of infection did not correspond to particular viral isolate and were not associated with the clinical phenotypes of the corresponding patients. Severe pathological outcomes were associated with higher viral replication, especially in alveolar areas, and with an exacerbated innate cellular immune response that was characterised by substantial phagocytic and cytotoxic cell migration into the lungs. Moreover, detrimental innate cellular responses were linked to the up-regulation of several proinflammatory cytokines and chemokines and the down-regulation of IFNα in the lungs. Additionally, severe lung lesions were associated with greater up-regulations of pro-apoptotic markers and higher levels of apoptotic neutrophils and macrophages. In conclusion, this study confirmed that the clinicopathological outcomes of pH1N1 infection in ferrets were not only due to viral replication abilities but also depended on the hosts’ capacities to mount efficient immune responses to control viral infection of the lung.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-014-0085-8) contains supplementary material, which is available to authorized users.

microRNAs Regulate Host Immune Response and Pathogenesis During Influenza Infection in Rhesus Macaques

“…In contrast to previous studies that reported increased CXCL8 expression in the lungs of H1N1 (A/CastillaLaMancha/RR5661/2009 and A/CastillaLaMancha/RR5911/ 2009)-infected ferrets, H1N1 (A/PR/8/34)-infected lung epithelial cells (1,47), and BAL of macaques infected with CA04 (19), the levels of this chemokine in the BAL did not change in our current study. This may be due to differences in tissues (lung vs. BAL) or severity of disease (the macaques in our study controlled viral replication more quickly than previously reported for CA04).…”

Involvement of the different lung compartments in the pathogenesis of pH1N1 influenza virus infection in ferrets

“…Alveolar areas were also shown to contribute to the influx of inflammatory cells by the up-regulation of IFNα, IL-6 and IL-8, at 12 hpi, and CCL3 and IFNγ, at 24 hpi. The up-regulation of IL-8, IFNγ and CCL3 has been related to lung recruitment of neutrophils, NK and T cells and the development of severe influenza infection [8, 14, 19, 29]. In addition, TNFα and IL-6 up-regulation mediate phagocytic inflammatory infiltration and the apoptosis of infected cells [10, 30], which has also been associated with severe lung lesions after IAV [7, 11, 31].…”

“…RIG-I is activated by the detection of viral RNA in replication and its activation has been associated with protective and enhanced T cell responses against infection and the induction of IFN responses [8, 36]. …”

“…For the detection of IAV antigen by immunohistochemistry (IHC), paraffin sections were stained with a primary antibody against the influenza A nucleoprotein (NP), as previously described [8, 24]. Briefly, an antigen retrieval step was performed using protease XIV (Sigma-Aldrich, USA) for 10 min at 37 °C, and then blocked for 1 h with 2% bovine serum albumin (BSA) (85040C, Sigma-Aldrich Química, S.A., Spain) at room temperature (RT).…”

“…Severe cases after pH1N1 infection are consequence of diffuse alveolar damage (DAD) [3], also termed interstitial pneumonia, triggered by the spread of pH1N1 infection from the upper to the lower respiratory tract [6, 7] and an exacerbated inflammatory host immune response [8–12]. Several hypotheses have been made about the mechanisms involved in the dysregulation of the host inflammatory response after pH1N1 and IAV infection.…”