- Volume 64, Issue 8, 1983

Rabbits and rhesus monkeys were injected with 3 × 105 units of human gamma interferon (IFN) prepared in human leukocyte suspensions. Circulating IFN was detected up to 4 h after intravenous administration. Intramuscular injection maintained a relatively stable serum IFN level of about 50 units/ml for 7 to 9 h. The results in both species were similar. Little or no circulating IFN was detected after subcutaneous injection of 3 × 105 units, but 1.5 × 106 units maintained about 50 units per ml of serum for 30 h. Pharmacokinetically, human gamma IFN resembled human alpha interferons rather than human beta IFN.

After intracerebral inoculation of adult C3H mice, the ‘docile’ strain of lymphocytic choriomeningitis (LCM) virus multiplied to high titre in several visceral organs. Although the virus content of lung, liver, spleen and brain was high, these mice did not die but became long-term carriers of the virus. Injection of mice with the same dose of the ‘aggressive’ strain of LCM virus resulted in much lower virus titres in these organs; nevertheless, 100% of the mice died within 7 to 9 days. The results presented here show that mice infected with the ‘aggressive’ virus do not die if treated with anti-interferon globulin. Under these conditions the titres of ‘aggressive’ virus were as high in the different organs as in mice injected with the ‘docile’ virus. These results are consistent with the hypothesis that inhibition of LCM virus multiplication in various organs by interferon results in a lethal disease. The possible mechanisms underlying this seemingly paradoxical phenomenon are discussed.

Processing of cricket paralysis virus capsid protein precursors in vitro was resistant to the effects of a number of protease inhibitors. Leupeptin was effective in preventing cleavage of capsid protein precursors, suggesting that the virus-specified protease may be a serine protease. Virus capsid proteins were produced more rapidly in vitro when rabbit reticulocyte lysate was supplemented with an extract of Drosophila melanogaster cells. This suggests that cellular proteases may be involved in rapid processing of high molecular weight capsid protein precursors.

An icosahedral RNA virus isolated from Pseudoplusia includens is described. Purified virus preparations contained particles 40 nm in diam. with a sedimentation coefficient of 190S and a density of 1.33 g/ml. The virus consisted of 13 to 14% nucleic acid with a base ratio of A:25.8%, U:20.9%, G:30.8%, C:22.5%. Polyacrylamide gel electrophoresis demonstrated that the mol. wt. of the single-stranded RNA is 1.9 × 106 and the mol. wt. of the major polypeptide is 55 000. The virus is not serologically related to the Trichoplusia ni and Antheraea eucalypti RNA viruses.

Maize stripe virus (MStpV) and rice stripe virus (RSV) were compared serologically, chemically and physically. Cross-reactions in agar gel double-diffusion and microprecipitin tests, and neutralization of MStpV infectivity by antiserum to either virus showed that MStpV and RSV are serologically related. Both viruses sedimented slowly and in a heterodisperse manner in rate-zonal sucrose gradients, and both had similar buoyant densities in CsCl. Large amounts of a low molecular weight non-capsid protein were found in plants infected with either virus. Only limited maize-to-maize transmission of RSV was obtained with Peregrinus maidis (Ashmead), the MStpV vector. This transmission, however, resulted in symptoms similar to those induced by MStpV. MStpV and RSV appear to be members of the same virus group.

The particles of two serologically unrelated viruses, Solanum nodiflorum mottle (SNMV) and lucerne transient streak (LTSV), contain linear single-stranded RNA-1 (mol. wt. approx. 1.4 × 106), and linear and circular RNA molecules of mol. wt. approx. 1.2 × 105 (RNA-2). SNMV RNA-2 is reported to be part of the virus genome, but LTSV RNA-2 is a satellite-like RNA which is not necessary for the replication of LTSV RNA-1 or for the production of virus particles. When inoculated alone, SNMV RNA-2 did not infect plants but when inoculated with LTSV RNA-1 it replicated, modified the symptoms induced by LTSV and was packaged in particles with the serological specificity of LTSV. Thus, SNMV RNA-2 behaves like a satellite RNA in its interactions with LTSV. LTSV cultures containing LTSV RNA-2 or SNMV RNA-2, or lacking RNA-2, were distinguishable by reactions in some plant species but their particles were indistinguishable serologically, in sedimentation rate and in buoyant density in CsCl.

The addition of actinomycin D (25 µg/ml) or cordycepin (1 mm) to protoplast cultures immediately after inoculation with particles of tobacco mosaic, tobacco rattle, tobacco ringspot or potato leafroll viruses resulted in a decrease in the proportion of protoplasts becoming infected, as judged by staining with fluorescent antibody to virus particles. A delay of a few hours between the inoculation and the addition of either inhibitor largely or completely eliminated this effect. In contrast, infection was unaffected by the addition of actinomycin D when the protoplasts were inoculated with RNA preparations from tobacco mosaic or tobacco rattle viruses.