Genetic Recombination between Vaccinia Virus Strains Distinct in Hemagglutinin Production and Plaquing Efficiency

Abstract

Oda (1965) reported the rescue of dermovaccinia (strain Dairen I) abortive infection by ncurovaccinia virus (strain IHD-T) in mouse fibroblastic L cells. The present study, however, provided no evidence for such, but gave evidence for the occurrence of genetic recombination between the viruses in L and HeLa cells. HeLa and L cells were infected simultaneously with strain Dairen I which produces hemagglutinin (H+) and replicates well in HeLa cells but only poorly in L cells, and strain IHD-T which is H-and multiplies well in both cells. Sixty-eight of 225 and 24 of 114 clone preparations from the mixed infection yields in L and HeLa cells, respectively, were mixtures of H+ and H-viruses. The remaining 157 and 90 clones contained only one type of virus, H+ or H-, and varied widely in the plaguing efficiency for L cells. This contrasted with the results from parent viruses. An interpretation is that the plaguing efficiency is controlled by multiple genes and genetic recombination between the two vaccinia viruses with differing plaguing efficiencies results in occurrence of recombinants demonstrating a variety of plaguing efficiency. Hemagglutinin production was an all-or-none character, no intermediates being found, and can readily be tested at the particle level by the plaque-hemadsorption technique. These points render hemagglutinin production as a suitable marker for the genetic studies in contrast to the polygenic plaguing efficiency.

Unmasking of Growth of Dermovaccinia Strain Dairen I in L Cells by Acid Treatment of Cells after Virus Adsorption

“…plaques on L monolayers. This is in contrast to our previous experience with the original DI strain in which 27 clones were tested in the same manner, and none formed plaques on L monolayers [1]. This observation suggests that the selection for viruses better adapted to L cells is operating, and agrees with the data of Tagaya et al who showed a heterogeneity of viral population of strain DI regarding the infectivity for L cells by clonal analysis using the immunofluorescence technique [9].…”

“…But the effect of washing is limited, and usually fails to reveal the slight growth of strain DI in L cells, as shown in this and previous studies [1,5]. The antiserum treatment is not available for this system since L cell sheets are destroyed to a considerable extent by the repeated washing required for the removal of the antiserum used [1].…”

“…Inactivation of Virus at Low pH A mixture of DI and IHD-T viruses, instead of individual virus suspensions, was used for the experiment, since the differential assay of the two viruses can readily be made by the plaque-hemadsorption method [1]. DI plaques become surrounded by a hemadsorption zone but IHD-T plaques do not when treated with fowl erythrocytes.…”

“…The viruses and the technique of infectivity assay and cell culture were the same as used in the previous study [1]. Strain DI of egg-adapted dermovaccinia virus was used, but also strain IHD-T of neurovaccinia virus was included in the study because, unlike strain DI, it grows well in L cells.…”

“…replicates poorly in L cells, and one can show titer rises only with difficulty [1,5,6,8]. Reduction by some means of residual active virus after virus adsorption would be effective to reveal its poor growth.…”