Optimization of immune strategy for a construct of Salmonella-delivered ApxIA, ApxIIA, ApxIIIA and OmpA antigens of Actinobacillus pleuropneumoniae for prevention of porcine pleuropneumonia using a murine model.

In this study, the Actinobacillus pleuropneumoniae antigens ApxIA, ApxIIA, ApxIIIA and OmpA were expressed in an attenuated strain of Salmonella (∆lon∆cpxR∆asd) for prevention of porcine pleuropneumonia. In order to evaluate the immunization strategy of the construct, a total 60 BALB/c mice were equally divided into four groups (n = 15). Group A mice were intranasally immunized only at 6-weeks-of-age, while group B mice were intransally primed and boosted at 6- and 9-weeks-of-age, respectively, and group C mice were intransally primed at 6-weeks-of-age and subsequently boosted twice at 9- and 12-weeks-of-age. Group D mice were used as a control, which were inoculated with sterile PBS. Groups A, B, and C showed significantly higher serum IgG and fecal IgA immune responses than those of the control group. After virulent challenge with a wild type A. pleuropneumoniae, the immunized groups A, B and C showed 33.3 %, 13.3 % and 26.7 % mortality as the control group showed 60 % mortality. These results showed that the protection against porcine pleuropneumonia using the construct can be optimized by a double intranasal vaccination.