In this case, the down-regulation of the cytolytic function of PBLs did not appear to be due to the production of viral IL-10 (vIL-10), which was frequently observed in NPC tumor tissue [43], because vIL-10 was not detectable in CNE2 cells by reverse transcription polymerase chain reaction analysis (data not shown). Here, IL10 is linked to nasopharyngeal carcinoma.