Oral immunization of swine with attenuated Salmonella typhimurium aroA SL3261 expressing a recombinant antigen of Mycoplasma hyopneumoniae (NrdF) primes the immune system for a NrdF specific secretory IgA response in the lungs

Salmonella typhimurium SL3261 (aroA mutant) expressing a recombinant Mycopl asma hyopneumoniae antigen was used to orally immunize swine against porcin e enzootic pneumonia. This construct, designated S. typhimurium aroA SL3261 (pKF1), expressed a recombinant protein containing the carboxy-terminal 11 kDa of a 42 kDa M. hyopneumoniae NrdF ribonucleotide reductase R2 subunit protein. Here we demonstrate that this antigen is present in all seven geog raphically diverse strains of M. hyopneumoniae tested, and is recognized by the swine immune system after experimental infection with the virulent M. hyopneumoniae Beaufort strain. The immune response of swine orally immunize d twice with S. typhimurium SL3261 (pKF1) on day 0 and day 14 was evaluated . Oral immunization with S. typhimurium SL3261 (pKF1) primed the immune sys tem to elicit a significant (P<0.05) secretory IgA response against the 15 kDa NrdF antigen in the respiratory tract of swine, post-challenge, compare d to control groups. Blood lymphocytes from swine immunized with S. typhimu rium SL3261 (pKF1) proliferated significantly (P<0.05) following stimulatio n with M. hyopneumoniae whole-cell extracts compared to control groups 14 d ays post-vaccination. Following challenge with virulent M. hyopneumoniae, s wine immunized with S. typhimurium SL3261 (pKF1) showed higher average dail y weight gains and reduced lung pathology compared to control groups.