The porcine reproductive and respiratory syndrome virus (PRRSV) is a rapidly evolving and diversifying pathogen for which there is a need for the development of improved vaccines.Immunity to PRRSV is not well understood although there are data suggesting that virus specific T cell IFN-gamma responses play an important role.We therefore aimed to better characterise the T cell response to European genotype PRRSV,with an emphasis on identifying and characterising the major T cell antigens.Groups of pigs (n=5) were experimentally infected with an attenuated subtype-1 strain (Olot91) or with a pathogenic subtype-3 virus (SUl-bel) and then challenged with the homologous viruses after 35 days.