Immune mechanisms against influenza
The avian influenza pandemics over the past years have triggered extensive research into the immune mechanisms of protection. Accumulating evidence indicates that immunity to avian influenza differs from that for seasonal strains of the virus. The EU-funded 'Identification of mechanisms correlating with susceptibility for avian influenza' (IMECS) initiative aimed to elucidate these mechanisms and provide essential knowledge for effective vaccine development. The major aspects of influenza-specific immunity such as humoral, cellular and innate responses were assessed. For this purpose, both general and specific population sub-groups such as infants and the elderly were involved in the study. The IMECS consortium studied specific groups of individuals who had been exposed to Spanish influenza or the H5N1 avian strain in Vietnam. This helped assess the effect of previous infections on different viral strains. Studies revealed that individuals with prior exposure to the Spanish flu sustained humoral antibodies against the pandemic strain H1N1. Evaluation of the antibody responses in individuals vaccinated with different strains of influenza verified good humoral responses against the vaccinated strain and variable responses against other strains. A particularly useful insight was obtained through the IMECS clinical trials. More specifically, seasonal influenza vaccination could potentially induce neutralising antibodies against the avian and pandemic influenza strains, especially in young individuals. The consortium also characterised T cell responses against influenza strains to identify viral epitopes that were remarkably conserved among viral sub-types. Interestingly, anti-influenza T cell responses increased in strength with age, possibly reflecting a compensatory mechanism for the reduced humoral immune responses. IMECS clinical work was accompanied by basic science studies such as the development of a pre-clinical mouse model for testing influenza vaccination. Various peptide vaccines were screened with promising results. Taken together, the results of the IMECS study emphasised the importance of influenza vaccination against seasonal and pandemic viral strains. Furthermore, they showed for the first time that the elderly require more potent vaccines. This has important implications for healthcare practices with regard to such viral infections.
