Localization of indoleamine 2,3-dioxygenase in human esophageal squamous cell carcinomas

Immunosuppressive factors derived from the tumor and nontumor cells present in the tumor microenvironment contribute to tumor escape from host immune attack. Recently, the tryptophan-catabolizing enzyme indoleamine 2,3-dioxygenase (IDO) derived from both the tumor cells and surrounding nontumor cells was found to function as a critical immunosuppressive factor. While the expression of IDO is intensively under investigation in many types of cancers, little information is available in esophageal squamous cell carcinomas (ESCC) thus far. In this study, we have therefore investigated the cellular localization of IDO in 45 ESSCs and ten morphologically normal esophageal tissues; the correlation of IDO with clinicopathological parameters was also analyzed. Immunohistochemistry (IHC) analysis revealed that the density of IDO-positive cells was increased in ESCCs relative to controls (P < 0.01). These cells were distributed as clusters and formed a patchy pattern in both the cancerous epithelium and the surrounding noncancerous cells. Double IHC further confirmed that many IDO-positive cells in the tumor stroma were smooth-muscle-actin-alpha-positive myofibroblasts, CD68-positive macrophages, and S100-positive dendritic cells. Statistical analysis showed that the densities of IDO-positive cells were not significantly correlated with tumor clinical parameters (tumor invasion depth, node metastasis, and TNM stages) and lymphocytic infiltration. Our current findings suggested that the increased IDO expression in ESCCs is from a mixed cellular source (both cancer cells and noncancerous cells). Further studies on immune cell functional analysis are required in the future.