Morphofunctional status and the role of mononuclear phagocyte system lung compartment in the pathogenesis of influenza A (H5N1) in mammals

Influenza and other respiratory viral infections account for 80%-90% of infectious pathologies. Influenza A (H5N1) virus has an apparent pneumotropism, and therefore the lung compartment of mononuclear phagocyte system plays an important role in antiviral immunity. Lung macrophages are active phagocytes expressing variety of antiviral factors. The investigation of morphofunctional status of lung macrophages and evaluation of their role in mammal antiviral response in a mouse model were performed within the study. Methods: Light microscopy using standard hematoxylin-eosin, and Van-Gizon’s picrofuchsin staining. Immunohistochemistry using influenza A antigen marker specific primary antibodies, myeloperoxidase, cathepsin D, lysozyme, NO synthase, pro-inflammatory cytokines, cells of CD68 macrophage lineage, PCNA proliferative activity. Morphometric and statistical analysis. Results: Influenza A virus antigen was detected in lung macrophages starting from day 1 to day 14 of infection which corresponds with the beginning of convalescence and may be suggestive of prolonged persistence of virus. On the one hand, the cytopathic effects of the virus lead to lung macrophages death mainly via apoptosis through activation of caspase cascade, including caspase-3 and caspase-9. On the other hand, the observed activation of PCNA proliferation marker, perhaps, allows to support the pool of lung macrophages not only by their recruitment from bone marrow but also by their proliferation in situ. The increase of mononuclear phagocyte system cells expressing antiviral factors depended on the stage of infection. In the early stage, there was an increase of number of cells expressing lysozyme, myeloperoxidase, cathepsin D, endothelial NO synthase (eNOS) followed by the increase of number of macrophages expressing inducible NO synthase (iNOS), pro-inflammatory cytokines and interleukins.