Changes in peripheral blood leukocyte populations in pigs with natural postweaning multisystemic wasting syndrome (PMWS)
Introduction
Postweaning multisystemic wasting syndrome (PMWS) is a recently described disease affecting late nursery and fattening pigs (Clark, 1997, Rosell et al., 1999), which is caused by porcine circovirus type 2 (PCV2) (Kennedy et al., 2000). Detailed pathological observations in natural and experimental cases of PMWS, using immunohistochemistry and in situ hybridization for detection of viral antigen and nucleic acid of PCV2 (Clark, 1997, Rosell et al., 1999, Kennedy et al., 2000), have identified the monocyte/macrophage lineage cells and other antigen-presenting cells in lymphoid organs as the main targets of PCV2 replication. Microscopic lesions characteristic of PMWS in lymphoid organs include multifocal to diffuse infiltration of lymphoid tissue by macrophages and/or multinucleate giant cells, and lymphocellular depletion of both follicle centers and parafollicular zones (Rosell et al., 1999). Pneumocystis carinii and Chlamydia spp., opportunistic pathogens commonly associated with immunosuppression, have been found in the lungs and intestine of PMWS affected pigs (Clark, 1997, Carrasco et al., 2000), and many pigs infected with PMWS had also pulmonary and/or septicaemic infections by bacteria such as Pasteurella multocida or Haemophilus parasuis (Madec et al., 2000). On the other hand, atypical lesions associated with Aujeszky’s disease virus (ADV) have been described in PMWS affected pigs (Rodrı́guez-Arrioja et al., 1999) Altogether, these observations suggest that pigs affected by PMWS may be immunocompromised.
However, to date, little information has been gathered on hematological and immunological parameters of PMWS affected pigs. In this study, changes in PBMC subsets were analyzed in pigs with PMWS by flow cytometry using a panel of specific mAbs. Values in diseased pigs were compared to those of a group of normal pigs.
Section snippets
Materials and methods
Two groups of pigs were used to compare PBMC subsets. The PMWS group included 13, 10-week-old pigs from a single farm (1300 sow, farrow-to-finish, commercial operation), showing growth retardation of recent onset (less than a week). PMWS in this farm was diagnosed the week before by demonstration of characteristic histopathological lesions and of PCV2 nucleic acid by in situ hybridization (ISH), associated to these lesions. This farm was selected for the study because of historic serological
Results and discussion
The diagnose of PMWS was confirmed in the group of diseased pigs (n=13) by detection of characteristic histopathologic lesions, and of PCV2 nucleic acid by ISH and PCR. Macroscopic findings associated with PMWS, such as enlargement of one or more lymph nodes, were found in most of the pigs; other lesions such as kidneys with multiple pale foci and lack of pulmonary collapse were sporadically observed. No macroscopic lesions were recorded in the group of healthy pigs. Characteristic microscopic
Acknowledgements
The authors thank Blanca Perez, Silvia Usero and Pere Losada for technical assistance. This work was partly funded by the Project QLRT-PL-199900307 from the fifth framework program 1998-2002 of the European commission, and the project 2-FEDER-1997-1341 from the I+D National plan (Spain).
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