SUSCEPTIBILITY OF THE SF9 INSECT-CELL LINE TO INFECTION WITH ADVENTITIOUS VIRUSES

Sf9, the insect cell line commonly used for gene expression by recombi nant baculovirus (BV), can be infected by St, Louis encephalitis (SLE) virus, a flavivirus, resulting in a persistent, productive, and cytop athic infection, while retaining the ability to be infected with a rec ombinant baculovirus (rBV). We now demonstrate using double immunofluo rescence that single cells are dually infected with SLE virus and rBV. Fourteen additional viruses including additional flaviviruses, other arbovirus classes, vesicular stomatitis virus (VSV), and herpes simple x virus, type 1 (HSV-I) failed to produce a cytopathic effect (CPE) in Sf9 cells. Plaque assays indicated infectious virus was present for s everal weeks postinoculation for Yellow fever (YF), Dengue types 1 and 2 (DEN-1 and DEN-2), Gumbo limbo (GL), Eastern equine encephalomyelit is virus (EEE), Western equine encephalomyelitis virus (WEE), HSV-1, a nd VSV viruses. For HSV-1, GL, EEE, WEE and VSV, but not for YF, DEN-1 or DEN-2 viruses, this could be attributed solely to survival in the Sf9 cell culture media. Of the 14 viruses tested, only HSV-1 could be detected after 2 weeks in serum-free media. The data indicate that sev eral viruses which are pathogenic for humans are stable for long perio ds of time at 27 degrees C in the serum-containing media used for cult ivation of Sf9 cells. YF, DEN-1 and DEN-2 viruses may replicate in Sf9 cells at extremely low levels. This suggests that adventitious agents which do not produce obvious CPE or interfere with rBV infection or r ecombinant protein expression could contaminate Sf9 cell cultures or m edia.