Expression of CXCL16 in human rectal cancer.

Local immunoregulation mediated by infiltration of inflammatory cells into colorectal adenocarcinomas is important for tumour progression. Tumour-associated macrophages and T cells are predominant components of chemokine-guided infiltrate of most colorectal tumours. CXCL16 is a newly discovered CXC chemokine expressed by antigen presenting cells attracting Th1, Tc and NK T cells. In this study, which is the first report on expression of the chemokine CXCL16 in human rectal cancer, CXCL16 gene and protein expression were analysed in cancer and normal adjacent tissue. Immunohistochemistry revealed CXCL16 expression in macrophages in normal tissue. The CXCL16 was found to a very limited extent in tumour-associated macrophages. Western blot analysis showed a suppression of CXCL16 protein in rectal cancer compared to non-cancer tissue in 83% of the patients (n=23, P=0.003). However, with real-time PCR mRNA was not down-regulated in the cancer compared to normal tissue, which may depend on regulated factor(s) at the level of translation and/or post-translation. The results may reflect one of the immunological mechanisms underlying carcinogenesis.