Social isolation stress enhanced liver metastasis of murine colon 26-L5 carcinoma cells by suppressing immune responses in mice

We investigated the effect of social isolation stress on the formation of e xperimental liver metastasis resulted from intraportal vein (i.p.v.) inject ion of colon 26-L5 carcinoma cells in male Balb/c mice, and elucidated some of the underlying mechanism involving the effects of this stress on cellul ar immunity. Increases in the colony number and tumor burden were observed in the mice socially isolated before and/or after tumor cell challenge, as compared with the group-housed mice. In addition, exposure of mice to 2 wee ks of preisolation resulted in decreases in the thymus weight and number of thymocytes by 35.8% and 40.2%, respectively, in comparison with the contro ls. Reduced proliferative response of splenocytes to various stimuli and su ppressed splenic NK activity, as well as decreased macrophage-mediated cyto toxicity, were also found in the mice exposed to social isolation. Thus, th ese results suggest that social isolation stress enhances tumor metastasis in part via its suppressive effect on the immune system of the host.