Chronic pneumonia in calves after experimental infection with Mycoplasma bovis strain 1067: Characterization of lung pathology, persistence of variable surface protein antigens and local immune response
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Medientyp:
E-Artikel
Titel:
Chronic pneumonia in calves after experimental infection with Mycoplasma bovis strain 1067: Characterization of lung pathology, persistence of variable surface protein antigens and local immune response
Erschienen:
Springer Science and Business Media LLC, 2012
Erschienen in:Acta Veterinaria Scandinavica
Sprache:
Englisch
DOI:
10.1186/1751-0147-54-9
ISSN:
1751-0147
Entstehung:
Anmerkungen:
Beschreibung:
<jats:title>Abstract</jats:title>
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<jats:title>Background</jats:title>
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<jats:italic>Mycoplasma bovis</jats:italic> is associated with pneumonia in calves characterized by the development of chronic caseonecrotic lesions with the agent persisting within the lesion. The purposes of this study were to characterize the morphology of lung lesions, examine the presence of <jats:italic>M. bovis</jats:italic> variable surface protein (Vsp) antigens and study the local immune responses in calves after infection with <jats:italic>M. bovis</jats:italic> strain 1067.</jats:p>
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<jats:sec>
<jats:title>Methods</jats:title>
<jats:p>Lung tissue samples from eight calves euthanased three weeks after experimental infection with <jats:italic>M. bovis</jats:italic> were examined by bacteriology and pathology. Lung lesions were evaluated by immunohistochemical (IHC) staining for wide spectrum cytokeratin and for <jats:italic>M. bovis</jats:italic> Vsp antigens and pMB67 antigen. IHC identification and quantitative evaluation of CD4<jats:sup>+</jats:sup> and CD8<jats:sup>+</jats:sup> T lymphocytes and immunoglobulin (IgG1, IgG2, IgM, IgA)-containing plasma cells was performed. Additionally, expression of major histocompatibility complex class II (MHC class II) was studied by IHC.</jats:p>
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<jats:sec>
<jats:title>Results</jats:title>
<jats:p>Suppurative pneumonic lesions were found in all calves. In two calves with caseonecrotic pneumonia, necrotic foci were surrounded by epithelial cells resembling bronchial or bronchiolar epithelium. In all calves, <jats:italic>M. bovis</jats:italic> Vsp antigens were constantly present in the cytoplasm of macrophages and were also present extracellularly at the periphery of necrotic foci. There was a considerable increase in numbers of IgG1- and IgG2-positive plasma cells among which IgG1-containing plasma cells clearly predominated. Statistical evaluation of the numbers of CD4<jats:sup>+</jats:sup> and CD8<jats:sup>+</jats:sup> T cells, however, did not reveal statistically significant differences between inoculated and control calves. In <jats:italic>M. bovis</jats:italic> infected calves, hyperplasia of bronchus-associated lymphoid tissue (BALT) was characterized by strong MHC class II expression of lymphoid cells, but only few of the macrophages demarcating the caseonecrotic foci were positive for MHC class II.</jats:p>
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<jats:sec>
<jats:title>Conclusions</jats:title>
<jats:p>The results from this study show that infection of calves with <jats:italic>M. bovis</jats:italic> results in various lung lesions including caseonecrotic pneumonia originating from bronchioli and bronchi. There is long-term persistence of <jats:italic>M. bovis</jats:italic> as demonstrated by bacteriology and immunohistochemistry for <jats:italic>M. bovis</jats:italic> antigens, i.e. Vsp antigens and pMB67. The persistence of the pathogen and its ability to evade the specific immune response may in part result from local downregulation of antigen presenting mechanisms and an ineffective humoral immune response with prevalence of IgG1 antibodies that, compared to IgG2 antibodies, are poor opsonins.</jats:p>
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