Abstract
I) Seroepidemiological analysis of various anti-EBV antibodies in NPC
In view of many suggestive findings in relation to the possible etiological role of EBV infection in NPC, seroepidemiological examinations were carried out of 141 sera from NPC-related patients and control groups. Particularly, anti-EBV-VCA (viral capsid antigen) and -EA (early antigen) antibodies were analysed with respect to IgG and IgA antibodies, respectively.
1) The geometric mean titers of these four antibodies were much higher in untreated NPC patients (VCA-IgG; 1: 848, EA-IgG; 1: 80, VCA-IgA; 1:64, EA-IgA; 1:19) than those in the control group (VCA-IgG; 1:116-320, three other titers; <1:10) containing healthy subjects. Also, the ratios of evaluation-positive cases for the four EBV antibodies were remarkably higher in the NPC patients (about 60-85%), than those in the control groups, showing NPC specificity of them.
2) Titers of anti-VCA- and anti-EA-IgA positively correlated with those of anti-VCA- and anti-EA-IgA each other in NPC patients.
3) Titers of these four antibodies in the NPC patients with good clinical prognosis following radiotherapy (RT) tended to remain unchanged or decreased slightly from the pre-RT values.
4) In general, the concentrations of IgG and IgA in NPC patients sera seemed to be relatively high, as compared to the normal sera, but no relations of IgG or IgA concentrations to the titer of anti-VCA-, anti-EA-IgG or anti-VCA-, anti-EA-IgA, respectively, were found.
II) Experimental confirmation of EBV infection in human epithelial cells by cell fusion, fluorescent antibody staining (FA) and the autoradiography (AR) method. Prior to cell fusion experiments, EBV-genome-positive lymphoid cells were labelled with 3H-thymidine and converted to grain-positive cells when examined by the AR method. Thereafter, experimental studies in vitro to confirm an etiological role of EBV in NPC were performed.
1) When EBV (+) and grain (+) lymphoid cells were fused with nasopharyngeal epithelial 2-27-Ad cells by the UV-inactivated HVJ (Sendai virus), EBV-determined nuclear antigen (EBNA) detectable by the FA method became evident in high frequency in 2-27-Ad grain (-) nuclei of heterokaryons several days after cell fusion. This evidence clearly means that the EBV-genome was transferred to epithelial cell nuclei, showing an establishment of EBV infection in this type of cell.
2) Other human epithelial Hep-2 cells fused with lymphoid cells by the similar procedures were found to behave in the same way but their frequency were not so high as in the case of 2-27-Ad cells.
3) When established epithelial or fibroblast cells derived from non-human origin (NHO) were employed instead of the above human origin cells, no EBNA was seen in NHO's nuclei of heterokaryons throughout the observation period.
