Abstract
Immunopathological events are key for the development of enzootic pneumonia (EP), which is macroscopically observed as cranioventral pulmonary consolidation (CVPC). This study aimed to investigate the putative association between the humoral immune response against Mycoplasma hyopneumoniae (M. hyopneumoniae) and prevalence and extension of CVPC in 1) experimentally infected pigs, 2) slaughtered pigs and 3) sequentially necropsied pigs in a longitudinal study. CVPC was scored by means of the European Pharmacopoeia recommended methodology. Specific IgG, IgG1 and IgG2 antibodies were assessed in serum. In addition, mucosal IgG and IgA antibodies were analyzed in broncho-alveolar lavage fluid (BALF) from experimentally challenged pigs. The systemic humoral immune response in experimentally infected pigs was delayed in onset whereas humoral respiratory mucosal immune response appeared more rapidly but declined earlier. Although low, BALF IgG antibodies showed the highest correlation with CVPC scores (r = 0.49, p<0.05). In slaughter-aged pigs, both percentage of lungs with CVPC and mean lung lesion score were significantly higher in M. hyopneumoniae seropositive farms compared to the seronegative ones (p<0.001). Similarly, seropositive sequentially necropsied pigs showed more severe CVPC than seronegative ones. Overall, mean serological values might help to forecast prevalence and severity of EP-like lung lesions using a population based approach. Remarkably, the specific systemic humoral immune response was found to be predominated by the IgG2 subclass, suggesting a dominant Th1-mediated immune response to M. hyopneumoniae.
Highlights
One of the main pulmonary lesions found in pigs on abattoir inspection is cranioventral pulmonary consolidation (CVPC) [1, 2]
The present study provides insight into those potential mechanisms of immunity that might be implicated in the pathogenesis of M. hyopneumoniae infection in pigs
This is the first study examining the involvement of different M. hyopneumoniae specific antibody isotype responses in lung lesion development
Summary
One of the main pulmonary lesions found in pigs on abattoir inspection is cranioventral pulmonary consolidation (CVPC) [1, 2]. Mycoplasma hyopneumoniae (M. hyopneumoniae) is considered the most important primary bacterial respiratory pathogen involved in such lung lesions. CVPC quantification by means of lung lesion scoring is frequently used to estimate the incidence and severity of lung lesions associated to M. hyopneumoniae infections, at experimental, herd and abattoir levels [4,5,6]. Post-mortem lung evaluation is an end-point parameter that does not provide information on the ongoing respiratory problems in any of the cases [6]. It would be of general interest to find an ante-mortem parameter that would provide reliable and real-time information in relation with CVPC prevalence and severity
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