Aims: To investigate the histopathological manifestations of two fatal cases of H7N9 influenza A virus infection.
Methods: Pulmonary and hepatic specimens from two fatal cases of H7N9 influenza virus infection were examined using H&E staining. Additionally, in situ hybridisation was performed with probes (ViewRNA) targeting H7N9 RNA and IP-10, interleukin (IL)-6 mRNA. The distribution of surfactant protein A (SP-A), surfactant protein B (SP-B), CD3, CD4, CD8, CD68 and C4d were determined with immunohistochemistry.
Results: Apart from the typical diffuse alveolar damage and hyaline membrane observed in severe influenza infection, we detected H7N9 RNA and massive intrapulmonary production of IP-10 and IL-6 mRNA using in situ hybridisation. Hyperplasia of type II pneumocytes was observed by H&E staining and immunohistochemistry. Proliferating macrophages and clustered neutrophils in the infected lungs were observed, whereas T lymphocytes, especially CD4T helper cells, were markedly depleted. No obvious complement deposition was found in lung tissues.
Conclusions: Our findings suggest that H7N9 influenza virus induced an immunological response towards overt pulmonary inflammation and systemic lymphopenia which led to intense alveolar damage and respiratory failure.
Keywords: H7N9 influenza virus; in situ hybridization; inflammatory response;.
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