DNA vaccine encoding type IV pilin of Actinobacillus pleuropneumoniae induces strong immune response but confers limited protective efficacy against serotype 2 challenge

► DNA vaccine encoding pilin protein ApfA was constructed against Actinobacillus pleuropneumoniae. ► Significant antibody response was generated following ApfA DNA vaccine immunization. ► The Th1, Th2 and mucosal immune responses can be induced by ApfA DNA vaccine. ► ApfA DNA vaccine induces strong antibody response but provides limited protection. ► Pilin should play a limited role in vaccine development against A. pleuropneumoniae.