Antibody- and cell-mediated immune responses of Actinobacillus pleuropneumoniae-infected and bacterin-vaccinated pigs

urrent bacterins afford minimal protection against Actinobacillus pleuropneumoniae in pigs by decreasing mortality but not morbidity. This lack of protection may be due to unsuitable or insufficient immune responses elicted by the bacterins. To better understand the type(s) of immune response associated with protection, antibody and cell mediated immune responses (CMIR) were examined in Caesarian-derived, colostrum-deprived Yorkshire piglets before and after A. pleuropneumoniae challenge. Serum antibody response, antibody avidity, delayed type hypersensitivity (DTH), and lymphocyte blastogenic responses were measured to the lipopolysaccharide (LPS), capsule (CPS), haemolysin (HLY), and outer membrane proteins (OMP) of A. pleuropneumoniae. Alterations in peripheral blood lymphocytes (PBL) subsets, in vivo T cell depletion and adoptive transfer of immune lymphocytes or serum to naive piglets were also performed to further clarify the type of response(s) relevant in protection against A. pleuropneumoniae infection. To compare responses which mediate complete or partial protection, piglets were either vaccinated twice with a commercial bacterin which gave partial protection, or were exposed to a low dose aerosol challenge of A. pleuropneumoniae CM5 (LD) which gave complete protection. PBL and sera were collected prior to and following primary and secondary immunization/infection, and high dose aerosol challenge. LD-infected piglets had more antibody (p...