OBJECTIVETo investigate the effects of Echinococcus multilocularis on host liver cell proliferation in vivo using a BALB/c mouse alveolar hydatid infection model.

METHODSSixty-five 8-10-week-old female BALB/c mice were randomly divided into an experimental group (n = 40) and a control group (n = 25) and administered an abdominal injection into the left liver lobe of E. multilocularis protoscolices in saline solution or saline solution alone, respectively. At post-injection day 2, 8, 30, 60, and 90, liver samples were collected for analysis of lesions and lesion-adjacent tissue by hematoxylin-eosin staining and differential expression of proliferating cell nuclear antigen (PCNA), cyclin D1, cyclin A, and cyclin B1 by immunohistochemical staining. The significance of intergroup differences was assessed by Student's t-test.

RESULTSThe control group showed normal liver histology at all time points. The experimental group developed E. multilocularis lesions that showed increased severity of pathological features, such as inflammatory cell invasion, steatosis and fibrous connective tissue hyperplasia, over time. At post-injection days 2 and 8, enlarged, binuclear and apocyte hepatocytes were observed close to the lesions. At post-injection days 30, 60, and 90, the number of hepatocytes expressing PCNA progressively increased in the experimental group, and the numbers were significantly higher than in the control group (7.01 +/- 1.89 vs. 1.03 +/- 0.52, 8.41 +/- 2.80 vs. 0.93 +/- 0.31, and 13.4 +/- 4.43 vs. 1.07 +/- 0.94; all P < 0.05). The same progressively increasing trend was seen in the number of hepatocytes expressing CyclinD1, but was only significantly different from controls at post-injection days 30 and 60 (6.73 +/- 2.52 vs. 0.48 +/- 0.43 and 8.22 +/- 3.09 vs. 0.55 +/- 0.34; both P < 0.05). In contrast, the number of hepatocytes expressing cyclin A was significantly increased at post-injection day 30 and then showed a decreasing trend at days 60 and 90, although the numbers of expressing cells remained significantly higher than control levels at all time points (7.75 +/- 3.05 vs. 0.69 +/- 0.36, 3.42 +/- 1.80 vs. 1.14 +/- 0.42, and 3.03 +/- 1.50 vs. 0.69 +/- 0.31; all P < 0.05). The number of hepatocytes expressing CyclinB1 in the experimental group was less robust than the other cyclins (with a general temporal trend of increase followed by decrease), but the differential expression was not significantly different from the control levels at any time point.

CONCLUSIONE. multilocularis infection may promote the expression of host factors related to proliferation and anti-apoptosis in liver. This pathogen-mediated modulation of host cell-survival mechanisms may provide a rationale explanation for the clinical observations of hepatomegaly and the unexpected survival of alveolar echinococcosis patients following major hepatic resection.