Physical changes of Wesselsbron virus occurring during attenuation in foetal lamb kidney cells

Summary

Two strains of Wesselsbron virus, one having undergone 12, the other 110 (attenuated strain) passages in foetal lamb kidney (FLK) cells were examined by means of a number of physical techniques.

Low passage virus was found to have densities of 1.225 and 1.238 g/ml when propagated in suckling mouse brain (SMB) and FLK cells, respectively, in caesium chloride density gradient centrifugation. High passage virus was found to consist of particles of two densities, 1.14 and 1.25 g/ml, irrespective of the cell system from which they were derived and a third component of buoyant density 1.35 g/ml emerging out of treatment of virus derived from SMB with lecithinase-C fromClostridium welchii and in untreated virus derived from FLK cells. Density differences and differences in the electrophoretic mobilities of two zone electrophoretic components are discussed in terms of differences in particle size as determined by ultrafiltration and confirmed by electron microscopy. A probable cause of these physical differences is the presence or absence of lipids. This is discussed.

Heat inactivation of Wesselsbron virus was biphasic, the attenuated strain being more heat labile. The attenuated strain had also lost the ability to agglutinate goose red blood cells.

That attenuation of Wesselsbron virus by passaging in FLK cells in tissue culture had resulted in accompanying physical changes was clearly evident.