ANTIBODY-MEDIATED AND CELL-MEDIATED IMMUNE-RESPONSES OF ACTINOBACILLUS PLEUROPNEUMONIAE-INFECTED AND BACTERIN-VACCINATED PIGS

Current porcine pleuropneumonia bacterins afford only partial protecti on by decreasing mortality but not morbidity. In order to better under stand the type(s) of immune response associated with protection, antib ody- and cell mediated immune responses (CMIR) were compared for pigle ts before and after administration of a commercial bacterin, which con fers partial protection, or a low-dose (10(5) CFU/ml) aerosol challeng e with Actinobacillus pleuropneumoniae CM5 (LD), which induces complet e protection. Control groups received phosphate-buffered saline or adj uvant, Serum antibody response, antibody avidity, delayed-type hyperse nsitivity (DTH), and lymphocyte blastogenic responses were measured an d compared among treatment groups to the lipopolysaccharide (LPS), cap sular polysaccharide (CPS), hemolysin (HLY), and outer membrane protei ns (OMP) of A. pleuropneumoniae, Peripheral blood lymphocytes and sera were collected prior to and following primary and secondary immunizat ion-infection and high-dose A. pleuropneumoniae CM5 (10(7) CFU/ml) aer osol challenge. Serum antibody and DTH, particularly that to HLY, diff ered significantly between treatment groups, and increases were associ ated with protection, LD-infected piglets had higher antibody response s (P less than or equal to 0.01) and antibody avidity (P less than or equal to 0.10) than bacterin-vaccinated and control groups. Anti-HLY a ntibodies were consistently associated with protection, whereas anti-L PS and anti-CPS antibodies were not, LD-infected animals had higher DT H responses, particularly to HLY, than bacterin-vaccinated pigs (P les s than or equal to 0.03), The LD-infected group maintained consistent blastogenic responses to HLY, LPS, CPS, and OMP over the course of inf ection, unlike the bacterin-vaccinated and control animals, These data suggest that the immune responses induced by a commercial bacterin ar e very different from those induced by LD aerosol infection and that c urrent bacterins may be modified, for instance, by addition of HLY, so as to stimulate responses which better reflect those induced by LD in fection.