Abstract: Objective   To investigate the expression and its significance of tumor necrosis factor-α (TNF-α) and caspase-3 protein in monocytes adjacent to the invaded Echinococcus multilocularis in liver.  Methods  40 female Kunming mice were randomly divided into experimental group (n=20) and sham operation (control) group (n=20). Mice in experimental group were infected with 20% E. multilocularis suspension (0.1 ml per mouse) through abdominal opening injection in liver and the mice in control group were injected with equal physiological saline. The mice were sacrificed at 6 months post-infection for observing the growth and metastasis of E. multilocularis. Pathological changes were observed by HE staining． The expression of TNF-α and caspase-3 protein in hydatid cyst and metastasis tissue were detected by immunohistochemistry staining and the apoptosis of the monocytes was measured by TUNEL．  Results  After 6 months post-infection, E. multilocularis were spread over the liver of the mice in experimental group. Metastasis rate of lymph nodes was 45.0%（9/20）. Infiltration of monocytes was observed around E. multilocularis in liver and lymph nodes with metastasis by HE staining. Immunohistochemistry showed that the positive expression rate of TNF-α and caspase-3 protein in monocytes was 100% and 100%, and 95% and 100% respectively around the cyst in experimental group, while the expression rate was only 5% and 0 respectively in the liver of the control mice (P＜0.01). The monocytes showed significant apoptosis by TUNEL in experimental group with a positive expression rate of 100%, with a significant difference between experiment group and the control (P＜0.01). Conclusion  In the process of alveolar Echinococcus infection, the high expression of TNF-α protein might be associated with the apoptosis of monocytes, which may inhibit the host immunological function.

Key words: Alveolar echinococcosis； Monocyte； Apoptosis； Tumor necrosis factor-&alpha