Evaluation of local and systemic immune responses induced by intramuscularinjection of a Mycoplasma hyopneumoniae bacterin to pigs

Objective-To evaluate immune responses induced by administration of Mycopla sma hyopneumoniae bacterin to pigs. Animals-60 healthy 7- to 10-day-old cross-bred boars. Procedure-Pigs were assigned to 1 of 4 pig groups (15 pigs/group): vaccinat ed, challenged; vaccinated, nonchallenged; nonvaccinated, challenged; nonva ccinated, nonchallenged. Vaccinated pigs received IM injections of a mycopl asma bacterin on days 0 and 14, whereas nonvaccinated pigs received saline (0.9% NaCl) solution. Pigs in the challenged groups were inoculated intratr acheally with M hyopneumoniae on day 42. Pigs were euthanatized and necrops ied 41, 44 48, and 70 days after the first vaccination, and proportion of l ung surface with pneumonic lesions was determined. Percentage of lymphocyte subpopulations and number of interferon-gamma (IFN-gamma) secreting lympho cytes in blood and tissues, cytokine and antibody concentrations in broncho alveolar lavage (BAL) fluid, and serum antibody concentrations were determi ned. Results-Vaccination against and infection with M hyopneumoniae induced a lo cal mucosal immune response in the respiratory tract of pigs. Proportion of lung surface with pneumonic lesions in vaccinated challenged pigs was redu ced on day 70, compared with nonvaccinated challenged pigs. Vaccination sti mulated the production of M hyopneumoniae-specific IFN-gamma secreting bloo d lymphocytes. Tumor necrosis factor-alpha concentration in BAL fluid on da y 70 was increased in nonvaccinated challenged pigs, compared with vaccinat ed challenged pigs. Conclusions and Clinical Relevance-Vaccination against M hyopneumoniae indu ced local, mucosal, humoral, and cellular immune responses. Moreover, vacci nation reduced the severity of lung lesions in challenged pigs, suggesting that mucosal antibodies, mediation of the inflammatory response, and cell-m ediated immune responses are important for control of mycoplasmal pneumonia in pigs.