CD21-dependent infection of an epithelial cell line, 293, by Epstein-Barr virus

Epstein-Barr virus (EBV) is invariably present in undifferentiated nasophar yngeal carcinomas, is found sporadically in other carcinomas, and replicate s in the differentiated layer of the tongue epithelium in lesions of oral h airy leukoplakia. However, it is not clear how frequently or by what mechan ism EBV infects epithelial cells normally. Here, we report that a human epi thelial cell line, 293, can be stably infected by EBV that has been genetic ally marked with a selectable gene. We show that 293 cells express a relati vely low level of CD21, that binding of fluorescein-labeled EBV to 293 cell s can be detected, and that both the binding of virus to cells and infectio n can be blocked with antibodies specific for CD21. Two proteins known to f orm complexes with CD21 on the surface of lymphoid cells, CD35 and CD19, co uld not be detected at the surface of 293 cells. All infected clones of 293 cells exhibited tight latency with a pattern of gene expression similar to that of type II latency, but productive EBV replication and release of inf ectious virus could be induced inefficiently by forced expression of the ly tic transactivators, R and Z. Low levels of mRNA specific for the transform ing membrane protein of EBV, LMP-1, as well as for LMP-2, were detected; ho wever, LMP-1 protein was either undetectable or near the limit of detection at less than 5% of the level typical of EBV-transformed B cells. A slight increase in expression of the receptor for epidermal growth factor, which c an be induced in epithelial cells by LMP-1, was detected at the cell surfac e with two EBV-infected 293 cell clones. These results show that low levels of surface CD21 can support infection of an epithelial cell line by EBV. T he results also raise the possibility that in a normal infection of epithel ial cells by EBV, the LMP-1 protein is not expressed at levels that are hig h enough to be oncogenic and that there might be differences in the cells o f EBV-associated epithelial cancers that have arisen to allow for elevated expression of LMP-1.