The N-Terminal Domain of RTX Toxin ApxI of Actinobacillus pleuropneumoniae Elicits Protective Immunity in Mice

We expressed three Actinobacillus pleuropneumoniae ApxI deletion derivatives to map the domain that could induce protective immunity. Antiserum to ApxI N-terminal covered by residues 40 to 380 was found to neutralize ApxI hemolytic activity but not ApxIII cytotoxicity. When used as a subunit vaccine in mice, this recombinant N-terminal fragment elicited protection against lethal infection with heterologous A. pleuropneumoniae serovars.