ENHANCED CYTOPATHIC EFFECT OF HUMAN CYTOMEGALOVIRUS ON A RETINAL-PIGMENT EPITHELIUM CELL-LINE, K-1034, BY SERUM-FREE MEDIUM

Although human cytomegalovirus (HCMV) predominantly infects epithelial cells in vivo, the majority of studies of HCMV gene expression and re plication have been conducted using non-epithelial cell lines in part because of the absence of a good experimental system using epithelial cells. To address the nature of epithelial cell infection, we investig ated the susceptibility of an epithelial cell line (K-1034) establishe d from the retinal pigment epithelium to HCMV infection. This cell lin e exhibited high susceptibility to HCMV, as evidenced by detection of one of the immediate early antigens, IE2, in the nuclei of more than 8 0% of K-1034 cells at 24h following inoculation at a multiplicity of i nfection of 3 plaque forming units per cell. However, the yield after one-step growth of HCMV in K-1034 cells was about twenty-fold less tha n that in human embryonic lung fibroblast cells. Cytopathic effect (CP E) on K-1034 cells was not prominent in medium supplemented with 10% f etal bovine serum and viral late antigens were detected in less than 5 % of K-1034 cells. Interestingly, infected cells expressing late antig ens and exhibiting CPE were markedly increased in serum-free medium, e ven though the yield of infectious HCMV and viral genome copy numbers were almost the same in the different serum concentrations, due to vir al instability in the absence of serum. Thus, the progression of late antigens expression and the induction of CPE in infected epithelial ce lls is influenced by physiological conditions, and are negatively regu lated by some serum factor.