Immune Responses to the Attenuated Mycoplasma hyopneumoniae 168 Strain Vaccine by Intrapulmonic Immunization in Piglets

To investigate the immune responses to the attenuated Mycoplasma hyopneumoniae 168 strain vaccine, 8-15 d old piglets were immunized with M. hyopneumoniae 168 strain vaccine by intrapulmonic route. And the specific IgG antibody in serum, lymphoproliferation, IFNγ, and specific secretory IgA (SIgA) antibody in bronchoalveolar lavage fluid were detected on 30 and 60 d post-immunization (DPI), respectively. On 60 DPI, all the pigs except for those in health control group were challenged with a field M. hyopneumoniae strain JS. Necropsy was performed on 30 d post-challenge (DPC). The results showed that IFNγ and specific SIgA were stimulated on surface of respiratory tract after immunization. And peripheral blood mononuclear cells could also be proliferated about 1.81 and 2.12 fold on 30 and 60 DPI when stimulated by M. hyopneumoniae protein in vitro. However, no serum IgG antibody against M. hyopneumoniae was detected during the whole immune phage. After challenge, vaccinated pigs were observed with only very slight histological lesion in individual lobes. None of vaccinated pigs showed any clinical signs. While the unvaccinated pigs from challenge control group showed varying degrees of clinical sign and severe macroscopical lesion of mycoplasmal pneumonia of swine (MPS). The result suggested that the attenuated M. hyopneumoniae 168 strain vaccine inoculated by intrapulmonic route could activate the systemic cellular immunity, the local mucosal immunity and IFNγ secretion in respiratory tract to against M. hyopneumoniae infection in piglets.