The influenza virus still causes hundreds of thousands of deaths globally, on top of morbidity and associated economic burden. We are currently at the height of efforts surrounding the development and employment of 'universal' vaccines against this virus, with clinical trials commencing on the most promising candidates. Despite this, the influenza virus poses more of a threat to human life than it ever has previously, with multiple subtypes of pandemic potential circulating around the globe. The key to current efforts lies in the priming of the immune system towards generating long lasting defences against conserved epitopes and conferring heterosubtypic immunity against the surface glycoprotein haemagglutinin. While vaccine strategies have expanded rapidly over recent years with the advent of 'headless' constructs as well as those derived from consensus, mosaic or chimeric sequences, the serological techniques to test how effective these vaccines are, have advanced less rapidly. Classical serological assays have been shown to be ineffective at detecting the antibodies which modern 'universal' vaccines strife to elicit, replaced by ELISA based approaches combined with mouse models measuring in vivo protection. In this thesis, an alternative method for the detection of heterosubtypic antibodies is used in depth across multiple platforms. Influenza pseudotypes have been employed using chimeric haemagglutinin constructs in a comprehensive project aimed at dissecting head and stalk directed antibodies present in human serum. Characterised broadly neutralising monoclonal antibodies have been tested on panels of influenza pseudotypes including divergent bat influenza viruses which hitherto have not been encountered in humans. A further aspect of influenza immunity has been covered in the detection of anti neuraminidase antibodies which have an important role to play in influenza heterosubtypic immunity. Finally, influenza pseudotypes bearing the glycoproteins from the less studied influenza B virus have been assayed in a large scale project aimed at correlating pseudotype assays with classical approaches
