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We detected the effect of non-toxic doses of sodium selenite (Se) on the expressing effect of nuclear antigen (EBNA) of Epstein-Barr virus (EBV) in Raji cell line by microfluorescence spectrophoto-quantitation (MFS) and studied the inhibing transformation in B lymphocytes from human umbilical cord blood (BL) with EBV in vitro by Se. We found that Se (0.01-0.50 microgram/ml) can lower EBNA-MFS value 8.4%-21.8% in Raji cell line. The transformation effect of BL with EBV was markedly inhibited by Se (0.1-1.0 microgram/ml) in pretreatment and cotreatment. The inhibition rates of BL transformation were 73.4%-92.1% and 60.3%-77.2% respectively. EBV is associated with nasopharyngeal carcinoma (NPC). The Se levels of serum and hair in NPC patients were markedly lower than those in healthy persons. The results suggest that supplement Se to persons for active expression of EBV gene and NPC patients may help protect againt and treat NPC and diseases associated with EBV.

Serological screening on nasopharyngeal cancer in 338,868 persons living in 21 cities and counties of Guangxi Zhuang Autonomous Region was carried out from January 1991 to September 1993. Results showed 9367 persons were positive for IgA antibodies to Epstein-Barr virus (EBV) capsid antigen, and 306 of them positive for IgA to EBV early antigen. One hundred and thirteen cases of nasopharyngeal cancer were detected in the former with 100 cases (88.5%) in the early stage, and 63 cases in the latter with 58 (92.1%) cases in the early stage. It suggested certain relationship existed between EBV and nasopharyngeal cancer, and serologic screening could be beneficial for secondary prevention of it.

In this study, we observed the effect of selenium (Se) on nasopharyngeal carcinoma (NPC) induced by dinitrosopi erazine (DNP) in rats through adding sodium selenite into drinking water. One hundred and sixty Wistar rats were divided into five groups: (1) blank control group (BG), no treatment; (2) Se control group (SG), given 50.7 mumol/L Se in drinking water for the first 3 weeks and then 31.7 mumol/L until the end of the experiment; (3) DNP control group (DG), injected subcutaneously 15mg/kg DNP twice a week from the 4th week to the 35th week; (4) Se prevention group (PG), given Se as done in SG and injected DNP as done in DG; (5) Se therapy group (TG), injected DNP as done in DG and given 50.7 mumol/L Se in drinking water from the 36th week to the end of the experiment. The experimental duration was one year. The result showed that there was no NPC in BG and SG and that the incidence of NPC in PG was reduced by 54.3% as compared with that in DG, which was significantly different (P < 0.01). In addition, the incidences of precancerous lesions of nasopharynx were significantly different between the two groups. But the incidences of NPC were not significantly different between TG and DG. In the process of carcinogenesis, the blood Se concentration of DG decreased. The blood Se concentration of rats could be elevated by supplementing Se in drinking water. Our result suggested that elevating the level of Se in rats can prevent the NPC.