Dendritic cell infiltration pattern along the colorectal adenoma-carcinoma sequence

We have previously reported that the dendritic cell (DC) functional index cytokine interleukin-12 was significantly decreased in colorectal carcinoma (CRC) tissues. In this study, the DC infiltration pattern and the density of mature DCs (mDCs; labeled by anti-CD83 and anti-CD208) and immature DCs (iDCs; labeled by anti-CD1alpha) were characterized using immunohistochemistry (IHC) in tissue samples from 23 patients with CRC, 33 patients with colorectal adenoma (CRA), and 19 healthy controls. In addition, the DC function inhibitor cyclooxygenase-2 (COX-2) and the downstream signal molecule prostaglandin E2 (PGE2) and related receptors EP2/EP4 were measured by quantitative real-time PCR and double immunofluorescence staining. The IHC analyses revealed changed densities of mDCs and iDCs in the tumor microenvironment; in CRA and CRC, the density of mDCs was decreased, but the density of iDCs was gradually increased. Furthermore, the distribution patterns of DCs were also altered. In CRA, mDCs were abundantly distributed in the subepithelial stroma of the adenomatous mass. In CRC, the distribution of mDCs in the tumor stroma was not homogeneous, and mDCs residing in the stroma at invading edges were more frequently found compared with in the intratumoral stroma (P<0.05). Increased iDCs were found in the intratumoral mass in CRC, and some infiltrated into the malignant epithelium. By quantitative real-time PCR, a gradually increased level of COX-2 mRNA was demonstrated in the local tissues along the adenoma-carcinoma sequence, and double immunofluorescence staining showed a colocalization of PGE2 receptors EP2/EP4 with mDCs in the stroma of CRC. In conclusion, our current findings revealed an altered DC infiltration pattern along the adenoma-carcinoma sequence; gradually increased COX-2 expression might contribute to the DC functional defect.