Detection and characterization of porcine endogenous retrovirus in porcineplasma and porcine factor VIII

The pig genome contains porcine endogenous retroviruses (PERVs) capable of infecting human cells. Detection of infectious retrovirus in porcine periph eral blood mononuclear cells and endothelial cells suggested to us that pig plasma is likely to contain PERV, Both PERV env sequences and viral revers e transcriptase (RT) activity were detected in all plasma samples isolated from four NIH minipigs. To detect infectious virus from plasma, we performe d a culture assay using three cell lines of feline, swine, and human origin that had previously been shown to be permissive for PERV, Infectious virus was successfully cultured from all four NIH minipig plasmas on the swine c ell line ST-IOWA. Using RT-PCR with env-specific primers, we could detect e xpression of PERV class C envelope in the supernatant of ST-IOWA cells that had been exposed to each pig plasma. We next examined a pig plasma derivat ive, Hyate:C (porcine factor VIII), and found evidence of PERV particles, s ince all six lots examined were positive for PERV RNA and RT activity. Howe ver, infectious virus could not be detected in clinical lots of Hyate:C, su ggesting that the manufacturing process might reduce the load of infectious virus to levels below detectable limits of the assay, Detection of infecti ous virus in porcine plasma confirms and extends the previous findings that certain porcine cells express PERV when manipulated in vitro and clearly d emonstrates that there are porcine cells that express infectious PERV const itutively in vivo.