| Summary: | The seasonal Influenza A viruses are respiratory pathogens causing epidemics annually with mild illnesses, while sporadically, novel influenza viruses emerge and trigger pandemics associated with more widespread and sometimes severe disease. The biological basis for severity of influenza disease remains unclear though it is recognized that the interplay between the influenza viruses and the host immune responses both contribute to viral pathogenesis. As macrophages are key sentinels of the innate immune response and play a crucial role in being the “first responders” as well as contributing to shaping the subsequent (pathogen‐specific) adaptive immune response, the objective of this research was to bring insights on the outcomes of the interactions of influenza viruses with the macrophages.
The occurrence of Antibody‐Dependent Enhancement (ADE) of Influenza infection in macrophages was investigated. ADE occurs when non‐neutralized virus‐antibody complexes find alternative entry routes into host cells, mainly through the Fc‐receptor pathway and has been demonstrated predominantly in macrophages. Addition of human serum from some individuals to influenza A virus (either H5 pseudoparticles or pandemic (H1N1) virus) led to enhanced infection of murine macrophage‐like cells as illustrated by a two to five fold increase in detection of influenza M‐gene copies. Immunofluorescence microscopy indicated that serum‐mediated pandemic (H1N1) infection led to an increase in the number of infected cells than in controls. As the fold change in viral gene copies paralleled the fold increase of infected cells I concluded that ADE infection provide pandemic (H1N1) virus with increased opportunity to infect cells rather than simply increase the viral load per cell. In order to strengthen our results, and make them more physiologically relevant, experiments were then performed with human primary cells with clinical sera. However, ADE was not demonstrated in primary human macrophages, suggesting that ADE may be cell type or host specific.
The second research question investigated was whether the different state of human primary macrophage differentiation or activation in vitro determined the susceptibility to influenza infection. Recently, work by others has shown a diverse range of macrophage phenotypes that arise by differences in macrophage differentiation and activation. In addition to the classical activation pathway (caMΦ), new mechanisms of activation, designated as alternative
activation (aaMΦ), have been reported. Classically and alternatively activated macrophages display different phenotypes and properties, such as molecule expression patterns, cytokine secretion, and gene signatures. This study constitutes the first systematic comparison of Influenza A virus infection of these different subsets of human primary monocyte‐derived macrophages. When assessed for their permissiveness to different influenza A viruses, aaMΦΦshowed greater susceptibility to influenza A infection than caMΦ. This work also documents the receptor patterns and the gene expression profile of these macrophages in response to influenza virus infection in vitro. The results point to differences in susceptibility of the classically and alternatively activated human macrophages to pandemic H1N1 and other influenza A viruses and reveal intrinsic differences between these macrophage subtypes. Further investigations are needed to define the cellular and molecular determinants that define susceptibility of different macrophage subsets to influenza A infection. === published_or_final_version === Public Health === Doctoral === Doctor of Philosophy
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