Immunochemical studies of Sindbis virus variants

Characterization of a Sinbis virus variant with altered host range

A variant of Sindbis virus which is much more infectious for mouse cells than the standard virus has been examined for biochemical properties which might be responsible for this biological difference. The variant has a much enhanced ability to adsorb to mouse plasmacytoma (MOPC 315) cells, but when these cells were pretreated with heparin, they were able to adsorb the standard virus almost as well as the variant. This suggested that there was a surface charge difference between variant and standard virus. Differential elution of the viruses from hydroxyapatite and the results of isoelectric focusing of the virion glycoproteins substantiate this interpretation. Both viral glycoproteins E1 and E2 from the variant were more negatively charged than those of the standard virus but we were unable to find changes in tryptic peptides of the variant. Differences were found in stability of the two virus strains to heat and proteolytic enzymes.

Isolation of a Sindbis virus variant by passage on mouse plasmacytoma cells

A variant of Sindbis virus has been isolated by growing a stock of virus, previously passaged on chicken embryo cells, in mouse plasmacytoma (MOPC 315) cells in suspension culture. An indirect immunofluorescence test and infective center assay showed that only a small fraction of cells could be infected by the stock wild-type virus, but that the population of virus accumulating after a few passages on the mouse cells had host-range properties distinct from the stock virus. The mouse-passaged virus retained its virulence for the original host and back-passaging of this virus on chicken cells did not change its newly acquired properties. Thus, this variant appears to be a genetically distinct form of Sindbis that adsorbs to and grows much better than the stock virus on several types of mouse cells including cultures of mouse macrophages.