Serum soluble interleukin-2 receptor (IL-2R) and immunohistochemical staining of IL-2R/Tac antigen in colorectal cancer

Background. In the present study, we investigated the sig nificance of serum soluble interleukin-2 receptor (IL-2R) as a tumor marker, and examined the existence and localiza tion of cells positive for IL-2R/Tac antigen in colorecta cancer tissues and their regional lymph nodes. Methods. The study included 155 patients with colorectal cancer. Levels of serum soluble IL-2R were measured by an enzyme-linked immunosorbent assay. In the tissues obtained from 18 patients, immunohistochemical staining was performed, with the use of the avidin-biotin-peroxidase complex technique, in which mouse anti-human IL-2R antibody was used. Results. The preoperative levels of serum soluble IL-2R in patients with colorectal cancer were significantly higher than those of normal controls (P = 0.0065). The levels of serum soluble IL-2R in patients with metastatic lymph nodes were also significantly higher than the levels in those without metastatic lymph nodes (P = 0.0258). Concerning tumor markers, there were significant differences in serum soluble IL-2R levels between patients who were positive and those who were negative for carcinoembryonic antigen (CEA) and between these who were positive and those who were negative for immunosuppressive acidic protein (IAP). In the immunohistochemical staining of IL-2R, 16 of the 18 patients (88.8%) showed IL-2R-positive cells in the colorectal cancer tissues. In regard to the metastatic lymph nodes, all of 5 patients (100%) showed IL-2R-positive cells. On the other hand, IL-2R-positive cells were not recognized in normal colorectal tissues and non-metastatic lymph nodes. Conclusion. These results suggest that activated T lymphocytes infiltrating into cancer tissues to play an antitumor role may release a large amount of the α-chain of IL-2R, resulting in the high levels of serum soluble IL-2R in patients with colorectal cancer.