Internal environment for growth of cancer cells in mice: hypothermia, anemia and lymphocytopenia

Abstract

The internal environment in tumor-bearing mice was investigated in detail. When EL-4 lymphoma cells (5 × 106 cells/mouse) were intraperitoneally inoculated into C57BL/6 mice, approximately 70% of the mice died by day 24. In this regard, the internal environment was compared between control mice, surviving mice and tumor-bearing mice which died. The most prominent sign was hypothermia (<34?C from day 16) seen in tumor-bearing mice which died. Control mice and surviving mice did not show such hypothermia (around 38?C). Other changes, including anemia and lymphocytopenia, were also seen in tumor-bearing mice which died, but not in control mice and surviving mice. Immunological study revealed that NKT cells, which have been previously identified to be the major effector lymphocytes against EL-4 cells, almost disappeared, especially in the liver of tumor-bearing mice which died. These results suggest that a specific internal environment might be required for continuous tumor growth in vivo. Such internal environmental factors include hypothermia, ane- mia and severe immunosuppression.