Conservation and mutation of viral interleukin-10 gene in gastric carcinomas and nasopharyngeal carcinomas.

The Epstein-Barr virus (EBV) BamHI-C fragment rightward reading frame 1 (BCRF1)-coded viral interleukin-10 (vIL-10), exhibits high homology with human interleukin-10 (hIL-10) gene. The protein product vIL-10, which shares some functional properties with hIL-10, primarily mediates immunosuppressive functions. To characterize the variations of the vIL-10 gene and to explore the association between vIL-10 gene variations and EBV associated diseases, the vIL-10 gene was analyzed (using direct sequencing) in 41 cases of EBV-associated gastric carcinoma (EBVaGC), 83 nasopharyngeal carcinoma biopsies, and 40 throat washing samples from healthy donors in Northern China. One silent mutation (c9980a) was observed in the majority of EBVaGC, nasopharyngeal carcinoma and throat washing samples (134/164, 81.7%). Two consensus mutations (V6M and G23S) were identified in the signal peptide region in some nasopharyngeal carcinoma and throat washing isolates. These results indicate that the pattern B95-8 (identical sequence to B95-8) is the dominant type among the EBV isolates from Northern China, while the pattern SPM (mutation in the signal peptide present only in nasopharyngeal carcinoma and throat washing isolates) seems more relevant with the EBV-positive nasopharyngeal and laryngopharyngeal epithelial cells. The conservation of vIL-10, with a few variations, suggests the critical role of the vIL-10 gene for EBV in gaining an advantage over the host's immune system.