Antibody response to Epstein-Barr virus Rta protein in patients with nasopharyngeal carcinoma: a new serologic parameter for diagnosis.

BACKGROUND: Nasopharyngeal carcinoma (NPC) is associated closely with Epstein-Barr virus (EBV). The authors previously reported that an EBV immediate-early gene, BRLF1, was expressed frequently in NPC tumors, and a significant elevation in immunoglobulin G (IgG) antibodies directed against BRLF1 gene product Rta was detected in NPC sera by a radioactive immunoprecipitation assay. To simplify and to make the detection more quantitative, an enzyme-linked immnunosorbent assay (ELISA) was developed in this study. METHODS: Antigen domains of Rta were identified further using an immunoprecipitation assay. Two glutathione-S-transferase (GST) recombinant Rta fragments (R150-GST and R185-GST) were prepared subsequently and were used as antigens in the ELISA. Serum samples derived from 51 patients with NPC patients, 115 non-NPC ENT patients, and 47 healthy volunteers were examined for the presence of antibodies directed against Rta. RESULTS: Among the patients with NPC, 74.5% showed a positive IgG response to R150-GST, and 62.7% showed a positive IgG response to R185-GST, with 80.4% positive for either fragment. In contrast, the reactions were positive in only 8.5% of healthy volunteers and 13.0% of control patients. When using a mixture of the two recombinant Rta proteins as coating antigens, the IgG positive responses were 82.3%, 10.6%, and 14.8%, respectively, in patients with NPC, healthy volunteers, and control patients. It is noteworthy that 51.0% of the NPC sera showed a positive immunoglobulin A (IgA) response, with none of the control patients showing obvious reactivity. Both the IgG response and the IgA response to Rta protein in patients with NPC were correlated with the IgA response to EBV early antigens and virus capsid antigens, the classic serologic markers used to diagnose NPC. CONCLUSIONS: The ELISA method described for the detection of IgG antibodies directed against recombinant Rta proteins is simple and reliable and may be useful as a serologic parameter for the screening and diagnosis of patients with NPC.