Abstract
The causes that lead malignant tumors to be lethal are not completely understood. However, patients are known to reach a state of immunosuppression in the late stages of the diseases. This impairment of immune responses in patients or animals bearing cancer is believed to be one of the most plausible causes of death. To explain this impairment, the presence of immunosuppressive factors with a wide variety of molecular sizes have been investigated. One factor was found to be IAP (immunosuppressive acidic protein), a kind of α1-acid glycoprotein. In mice, an increase in the amount of IAP in the serum paralleled with the appearance of suppressor macrophages. In humans, many clinical reports tell us that after a surgical operation an increase in IAP in the serum clearly indicates the unfavourable prognosis of patients, while a decrease in IAP, followed by no later elevation, means a favourable prognosis. Other low-molecular weight immunosuppressive factors were looked for in ascites of tumor-bearing mice, based upon the evidence that the components of malignant cells which cause them to differ qualitatively from normal cells are transfer ribonucleic acids (RNAs). The breakdown products of these RNAs were examined by means of high performance liquid chromatography in mouse ascites and 1-methyladenosine (m1A) was detected, in addition to uric acid, uracil and pseudouridine. It was found that the administration of a μg order of m1A to mice two or three days before i.v. infection with Listeria monocytogenes caused a definite acceleration in the number of deaths due to infection. Both of these markers will be useful in the prognosis of cancer patients and monitoring the effectiveness of therapy. However, further knowledge of these immunosuppressive factors will be necessary in order to effectively diagnose the immunological status of cancer patients and establish a therapeutic policy for them. Because, without enough knowledge of these immunosuppressive factors, one can not deal with the real immunological status of cancer patients nor establish a therapeutic policy for them.
