Bronchiolitis obliterans organizing pneumonia in Swine associated with porcine circovirus type 2 infection

Abstract

Bronchiolitis obliterans organizing pneumonia (BOOP) is a chronic respiratory disease. Although the pathogenesis of BOOP is still incompletely understood, BOOP is responsive to steroids and has a good prognosis. In our five pigs with chronic postweaning multisystemic wasting syndrome (PMWS), typical BOOP lesions were revealed. All five porcine lungs showed typical intraluminal plugs, and porcine circovirus type 2 (PCV2) was identified. They also exhibited similar pathologic findings such as proliferation of type II pneumocytes and myofibroblasts (MFBs), extracellular collagen matrix (ECM) deposition, and fragmentation of elastic fibers. MFBs migration correlative molecules, for instance, gelatinase A, B and osteopontin, appeared strongly in the progressing marginal area of polypoid intraluminal plugs of fibrotic lesion. These molecules colocalized with the active MFBs. Both gelatinase activity and intercellular level of active MFBs were significantly increased (P < .05). Porcine chronic bronchopneumonia leads to BOOP and it is associated with PCV2 persistent infection. Swine BOOP demonstrates similar cellular constituents with human BOOP. Perhaps their molecular mechanisms of pathogenesis operate in a similar way. Thus we infer that the swine BOOP can be considered as a potential animal model for human BOOP associated with natural viral infection. Moreover, it is more convenient to obtain samples.

Figure 1

Detection of porcine circovirus type 2 (PCV2) with PCR method. The primers designed on the basis of the ORF2 of the PCV2 virus genome to produce a 416 bp long amplicon. The BOOP lung tissues from five pigs were positive. In the agarose gel, three representative cases were shown. Neg: negative control. M: leader. Lanes 1–3: BOOP lung samples. Lanes 4–6: normal lung samples from SPF pigs (n = 5, six replicates in each individual BOOP or normal pig).

Figure 2

Confirmation of PCV 2 antigen in BOOP lesion. PCV 2 antigen signals appeared strong positive in the foamy alveolar macrophages ((a)-(b), arrow head) and intraluminal plugs of two representing BOOP lesions. The other lung sections in five individual BOOP pigs revealed the similar results (n = 5, six replicates in each individual pig; Bar = 50 μm).

Figure 3

Histopathological constituents of BOOP lesion in specific staining. The representative picture showed the intraluminal plugs of loose connective tissue that occlude bronchioles in H&E stain (a). A large mount accumulation of collagen matrix was sawn cherry in picrosirius red stain (b) and strongly blue in OPIC stain (c) at the evaginated BOOP lesion. The elastic fibril revealed disruption and fragmentation in peribronchial alveolar septa ((c), arrow head) as compared to normal lung ((c) upright panel, arrow head). The proliferative cells of the intraluminal plugs and alveolar septa were identified as α-SMA positive MFBs (d) and OPN positive cells (e). MMP-2 (f) and MMP-9 (g) seemed to be expressed actively at the margin of intraluminal plugs of bronchioles as macrophage and myofibroblasts. The results shown represent one of six replicates in each independent experiment demonstrating similar results (P < .01 versus normal group). (Bar = 50 μm).

Figure 4

Metalloproteinase activity in BOOP tissues. The gelatin zymography revealed MMPs activity from three representative BOOP and normal pigs (a). For each individual BOOP or normal pig, six sample lung sections were evaluated for MMP activity and averaged. Then, the averages from the BOOP and normal animals were pooled from the five different pigs to generate the data presented (b). The activities of proMMP-9, MMP-9, proMMP-2, and MMP-2 were all significantly increased in BOOP group ((b), P < .05). *P < .05 versus normal group (n = 5, six replicates in each individual pig).

Figure 5

Quantitation of MFBs by alpha-SMA expression level. The Western blotting picture revealed that alpha-SMA expression level was increased in three representative BOOP cases (pigs) (a). The quantitative data were assayed from five cases (six lung sections in each case). Significant elevation of α-SMA expression in BOOP group was revealed (P < .05) (b). *P < .05 versus normal group (n = 5, six replicates in each individual BOOP or normal pig).