Susceptibility and production of a feline endogenous retrovirus (RD-114 virus) in various feline cell lines.

RD-114 virus is a replication-competent feline endogenous retrovirus that has been classified as a xenotropic virus. In this study, we examined the expression of the receptors for RD-114 virus in feline cell lines by conducting a pseudotype virus infection assay. Six out of eight feline cell lines were susceptible to the RD-114 pseudotype virus and two cell lines (MCC and FER cells) were resistant. The two resistant cell lines and one cell line (CRFK cells) weakly sensitive to the RD-114 pseudotype virus were found to produce replication-competent RD114-like viruses by the LacZ marker rescue assay and the interference assay. These data strongly suggest that RD-114 virus is polytropic and resistance to RD-114 virus in certain cell lines is due to receptor interference but not polymorphism of the RD-114 receptors. In addition, we determined the amino acid sequences of the envelope region of RD-114-like viruses produced from MCC, FER and CRFK cells. The sequences were identical with the authentic RD-114 virus. Because many feline cell lines are used to manufacture live attenuated vaccines for companion animals, attention should be paid to contamination of the RD-114 virus in vaccines.