Interleukin-10 expression and cytotoxic-T-cell response in Epstein-Barr-virus-associated nasopharyngeal carcinoma

Interleukin-10 (IL-10) is an inhibitory cytokine produced by various cell types. It exhibits strong sequence homology to BCRF-1 (viral IL-10, vIL-10), an open reading frame in the Epstein-Barr-virus (EBV) genome. Using in situ hybridization (ISH), polymerase chain reaction (PCR) and immunohistochemistry, we checked 41 cases of nasopharyngeal carcinoma (NPC), to study the presence of EBV in the tumor cells, as well as to clarify the relationship between IL-10 expression of the tumor cells and the response of cytotoxic T cells. IL-10 expression was studied by immunohistochemistry; as a result, 29 of 41 cases expressed EBER-1 RNA of EBV by ISH. In addition, 19 of the 29 with EBV and 9 of 12 without EBV cases expressed IL-10 in the tumor cells. The number of cytotoxic T cells increased in the tumor tissue, and the increase in the intratumoral stroma was stronger than in the remaining normal epithelia. The number of cytotoxic T cells also significantly increased in the cases with EBV. On the other hand, in the IL-10-positive series, the number of cytotoxic T cells decreased significantly more than in IL-10-negative series. In view of the established inhibitory effects of IL-10, expression of IL-10 may therefore be one of the mechanisms for NPC cells as well as EBV to counter local immune defense. However, we could not conclude whether or not IL-10 expression was directly induced by EBV.