title: Vaccination reduces macrophage infiltration in bronchus-associated lymphoid tissue in pigs infected with a highly virulent Mycoplasma hyopneumoniae strain.
abstract: BACKGROUND
  Mycoplasma 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.
  
  
  RESULTS
  The 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.
  
  
  CONCLUSIONS
  In 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.
authors.affiliation: Department of Pathology, Bacteriology and Avian Diseases, Ghent University, Faculty of Veterinary Medicine, Salisburylaan 133, B-9820 Merelbeke, Belgium. Katleen.Vranckx@telenet.be
authors.forename: Katleen
authors.initials: K
authors.lastname: Vranckx
authors.forename: Dominiek
authors.initials: D
authors.lastname: Maes
authors.forename: Silvana B
authors.initials: SB
authors.lastname: Marchioro
authors.forename: Iris
authors.initials: I
authors.lastname: Villarreal
authors.forename: Koen
authors.initials: K
authors.lastname: Chiers
authors.forename: Frank
authors.initials: F
authors.lastname: Pasmans
authors.forename: Freddy
authors.initials: F
authors.lastname: Haesebrouck
mesh_terms: D000818:Animals; D001428:Bacterial Vaccines / Q000276:immunology*; D001980:Bronchi / Q000166:cytology*; D008221:Lymphoid Tissue / Q000166:cytology; D008264:Macrophages / Q000502:physiology*; D045705:Mycoplasma hyopneumoniae / Q000472:pathogenicity*; D045729:Pneumonia of Swine, Mycoplasmal / Q000382:microbiology / Q000517:prevention & control*; D016133:Polymerase Chain Reaction / Q000662:veterinary; D013552:Swine; D013553:Swine Diseases / Q000382:microbiology*; D014774:Virulence
chemical_list: D001428:Bacterial Vaccines