Changes of splenic macrophage during the process of liver cancer induced by diethylnitrosamine in rats

It is generally accepted that spleen plays a complex role in the tumor immunity, which would change in the different periods of cancer. In this study, we investigated the changes in the function of splenic macrophage (Mphi) in different stages of liver cancer induced by diethylnitrosamine (DEN) in rats. The aim was to support the characteristics of "two-way" and "phase" of spleen in tumor immunity.

The model of pulmonary metastasis of liver cancer was established in forty male SD rats by DEN. In the 8th, 13th and 16th week, 10 rats were randomly chosen and sacrificed, and divided into cirrhosis, liver cancer and pulmonary metastasis groups depending on the pathological result, respectively. The other 10 rats were taken as control group. The Mphi was isolated by anchoring cultivation. The changes in ultrastructure, phagocytosis, cytokine secretion, antigen processing and presenting, and viability of splenic Mphi were detected by transmission electron microscopy, Vybrant(TM) Phagocytosis Assay, DQ(TM) Ovalbumin, and rat TNF-alpha ELISpot kits.

Under the electron microscope, the Mphi in the control group had some pseudopodium-like prominences, and mitochondria, ribosome, rough endoplasmic reticulum, lysosome can be found in the cytoplasm, and phagocytized RBC. In the liver cirrhosis and liver cancer group, Mphi had more prominences, meanwhile much more mitochondria, ribosome, rough endoplasmic reticulum, lysosome can be found in the cytoplasm, especially in the liver cancer group. In the pulmonary metastasis group, the Mphi was swelling, with few organelle. As compared to the control group, the function of splenic Mphi increased in cirrhosis and cancer groups, but decreased in metastasis group (phagocytosis rate: (84.7 +/- 1.9)%, (89.5 +/- 3.1)%, and (36.0 +/- 2.6)% vs (75.6 +/- 1.7)%, P < 0.05, P < 0.01; viability: (1.53 +/- 0.15)%, (1. +/- 0.14)%, and (1.12 +/- 0.29)% vs (1.48 +/- 0.17)%, P < 0.05, P < 0.01; TNF-alpha secretion: (741.0 +/- 52.9)%, (1126.2 +/- 174.5)%, and (313.8 +/- 50.8)% vs (626.6 +/- 24.6)%, P < 0.05, P < 0.01; positive cell rate of antigen processing and presenting: (24.03 +/- 1.87)%, (27.95 +/- 2.63)%, and (10.46 +/- 2.16)% vs (16.45 +/- 1.86)%, P < 0.01).

In the stage of cirrhosis and early cancer, the immune functions of splenic Mphi were reinforced. It may promote the non-specificity tumor immunity. On opposite, in the stage of pulmonary metastasis, the immune functions of splenic Mphi were impaired. It may lead to the decrease of tumor immunity.