The mechanism of Epstein-Barr virus infection in nasopharyngeal carcinoma cells.

To investigate the relationship between Epstein-Barr virus (EBV) and nasopharyngeal carcinoma (NPC) cells, we examined the pathway of EBV infection in NPC cell lines. We used immunolocalization to investigate the EBV receptor (C3d-R) and polymeric immunoglobulin receptor [secretory component (SC) protein]. We incubated IgA anti-EBV and EBV particles with NPC cells and observed the EBV DNA signal by in situ polymerase chain reaction hybridization and polymerase chain reaction plus Southern blotting. We also colocalized SC protein and EBV RNA in NPC biopsy specimens. Results showed that: 1) NPC cells did not express the EBV receptor but did express SC protein in each line; 2) SC protein was also expressed in some tumor cells but not in untransformed squamous metaplastic epithelia in NPC biopsy specimens; 3) EBV could infect NPC cells through an EBV-IgA and SC complex and retained an EBV viral genome in their nuclei; SC expression could be down-regulated by EBV proteins; and 4) in biopsy specimens, a fraction of tumor cells showed SC protein expression; only a portion of tumor cells contained EBV, and of these cells only a few expressed SC protein. These findings indicate that EBV cannot infect untransformed nasopharyngeal squamous metaplastic epithelia but can enter NPC cells through IgA-mediated endocytosis.