Vaccination reduces macrophage infiltration in bronchus-associated lymphoid tissue in pigs infected with a highly virulent Mycoplasma hyopneumoniae strain

Abstract

BackgroundMycoplasma hyopneumoniae is the causative agent of enzootic pneumonia and is responsible for significant economic losses to the pig industry. To better understand the mode of action of a commercial, adjuvanted, inactivated whole cell vaccine and the influence of diversity on the efficacy of vaccination, we investigated samples from vaccinated and non-vaccinated pigs experimentally infected with either a low (LV) or a highly virulent (HV) M. hyopneumoniae strain. Non-vaccinated and sham-infected control groups were included. Lung tissue samples collected at 4 and 8 weeks post infection (PI) were immunohistochemically tested for the presence of T-lymphocytes, B-lymphocytes and macrophages in the bronchus-associated lymphoid tissue (BALT). The number of M. hyopneumoniae organisms in bronchoalveolar lavage (BAL) fluid was determined using quantitative PCR at 4 and 8 weeks PI. Serum antibodies against M. hyopneumoniae were determined at 0, 2, 4, 6 and 8 weeks PI.ResultsThe immunostaining revealed a lower density of macrophages in the BALT of the vaccinated groups compared to the non-vaccinated groups. The highest number of M. hyopneumoniae organisms in the BAL fluid was measured at 4 weeks PI for the HV strain and at 8 weeks PI for the LV strain. Vaccination reduced the number of organisms non-significantly, though for the HV strain the reduction was clinically more relevant than for the LV strain. At the level of the individual pigs, a higher lung lesion score was associated with more M. hyopneumoniae organisms in the lungs and a higher density of the investigated immune cells in the BALT.ConclusionsIn conclusion, the infiltration of macrophages after infection with M. hyopneumoniae is reduced by vaccination. The M. hyopneumoniae replication in the lungs is also reduced in vaccinated pigs, though the HV strain is inhibited more than the LV strain.

Efficacy of early Mycoplasma hyopneumoniae vaccination against mixed respiratory disease in older fattening pigs

“…By using qPCR, Vranckx and others (2012b) recently showed that vaccination also significantly reduced the number of M hyopneumoniae organisms in the lungs of experimentally infected pigs. The fact that M hyopneumoniae DNA could still be detected by PCR confirms previous results from previous experimental and field transmission studies with different M hyopneumoniae vaccines (Meyns and others 2006, Villarreal and others 2011b).…”

Update onMycoplasma hyopneumoniaeinfections in pigs: Knowledge gaps for improved disease control

“…Vaccination reduces clinical signs and lung lesions and improves performance. Also, commercial vaccines reduce the number of organisms in the respiratory tract (Meyns et al., ; Vranckx et al., ) and decrease the infection level in a herd (Sibila et al., ). However, studies under experimental (Meyns et al., ) and field conditions (Pieters, Fano, Pijoan, & Dee, ; Villarreal et al., ) showed that vaccination conferred only a limited reduction in the transmission ratio of M. hyopneumoniae .…”

“…Vranckx et al. () reported a lower infiltration of macrophages in the lung tissue in vaccinated animals upon infection with M. hyopneumoniae , indicating that vaccination modulates the immune response following infection. The importance of local mucosal antibodies remains unclear.…”

Establishment of an antibody avidity test to differentiate vaccinated cattle from those naturally infected with Mycoplasma bovis

“…The usefulness of booster immunisation has been observed with vaccines against M. hyopneumoniae in pigs (Vranckx et al, 2012) and also with a vaccine against contagious caprine pleuropneumonia in goats and sheep (Nicholas and Churchward, 2012). However, it is generally believed that a specific interferon (IFN)-γ producing CD4 + Th1-like T-cell response is correlated with resistance to mycoplasmosis, such as Mycoplasma mycoides subsp.…”