- Volume 42, Issue 1, 1979

Lymphocytic choriomeningitis virus was purified from cell culture fluid by density gradient centrifugation in colloidal silica. The specific infectivity increased 5000-fold and the recovery of infectivity was about 10%.

Mice were inoculated in the left hind footpad with street rabies virus, and 24 h later various types of rabies vaccine were administered intramuscularly in the right leg. The vaccines alone were ineffective in reducing mortality, but when an interferon inducer, polyriboinosinic acid-polyribocytidylic acid complexed to poly-l-lysine (polyICLC), was given along with the vaccines, a marked reduction resulted. The polyICLC-vaccine combination was effective even when it was injected 5 days after infection, suggesting that effective postexposure treatment in man might be successful when given at a comparable late time.

Equilibrium density gradient centrifugation in CsCl confirms that DNA synthesized after vaccinia virus infection of HeLa cells is homogeneous in buoyant density and thus in base composition and is similar in this respect to bulk HeLa cell DNA. In contrast, rate sedimentation in alkaline sucrose gradients distinguishes two main classes of virus-induced DNA, neither of which can be equated with cell DNA synthesized in the same cultures prior to infection. The slower sedimenting class of virus-induced DNA co-sediments with DNA from purified virus particles: the second class sediments faster than pre-labelled cell DNA. Heterogeneity of virus-induced DNA does not result from fragmentation of radioactively labelled DNA, virus-mediated breakdown of cell DNA or association with either proteins or polyamines. Both slow and fast sedimenting classes of virus-induced DNA contain sequences complementary to all restriction endonuclease Hind III-specific fragments of the virus genome. The multiple species of DNA synthesized after infection are distinguished further by the effect of ethidium bromide. At a concentration which prevents the formation of infectious progeny virus, this compound inhibits selectively the de novo synthesis of that class of virus-induced DNA which sediments faster in alkaline sucrose gradients.