Some host-agent interactions of mycoplasmal pneumonia of swine
Abstract
Mycoplasmal pneumonia of swine (MPS) is one of the most important and economically significant diseases affecting the swine industry. Although clinical signs, gross, and histopathologic lesions of MPS have been well studied, the pathogenesis remains poorly understood. The role of humoral and cell-mediated immune responses in the development of the disease remains to be elucidated. The studies reported in this thesis were undertaken to investigate some aspects of the interactions between the host and agent of the disease. The protection conferred by passively acquired antibodies against experimental inoculation with virulent Mycoplasma hyopneumoniae was investigated. Pigs that had received immune serum (up to 2ml/kg of body weight) were not protected against challenge with M. hyopneumoniae P-5722-3 challenge material and were positive for mycoplasmal pneumonia by all measured criteria. It is possible that the amount of antibodies necessary to confer immunity is higher than 2ml/kg. It is also possible that the cellular immunity plays the major role in protection against the mycoplasmal organism. The role of the alveolar macrophage in the pathogenesis of the disease was investigated to better characterize the importance of the cellular immunity in the development of the disease. Alveolar macrophages from recovered pigs had increased secretory capabilities as determined by enhanced production of TNF-$\alpha$, suggesting a higher activation state than susceptible pigs. The phagocytic capabilities of alveolar macrophages were investigated using a bactericidal bioassay. The percentage of bacterial killing was not significantly different between recovered and susceptible animals. It appears that the modulation of the inflammatory response by releasing chemical mediators is the most significant role of the alveolar macrophage in recovered pigs. The cellular immunity, not humoral, appears to be the most important in the protection against M. hyopneumoniae infection. The early structural response in lungs of recovered and susceptible pigs following M. hyopneumoniae challenge was studied by electron microscopy. Although mycoplasmas were present in rechallenged pigs, no morphological differences were observed between rechallenged, recovered or uninoculated control pigs indicating complete healing 3 months after inoculation; a rechallenge did not enhance morphological changes.
Degree
Ph.D.
Advisors
Alstine, Purdue University.
Subject Area
Pathology|Veterinary services|Animal diseases
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