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Abstract
The neutralization of Bryan standard strain Rous sarcoma virus (bs-RSV) followed first-order kinetics after 15 min. incubation. No non-neutralizable fraction was observed when about 105 focus-forming units of representatives of subgroup A and subgroup B viruses were neutralized by homologous sera.
The antigenicity of a strain of bs-RSV was changed by growth on relatively resistant cells. The antigenicity of an A subgroup bs-RSV ‘pseudotype’ was changed by semi-cloning the virus. Both changes of antigenicity were expressed by a change of slope and a reduction of titre on cross-neutralization by the parent virus antiserum.
Antisera to a number of subgroup A leukosis viruses were examined for neutralization of the homologous bs-RSV ‘pseudotype’ and other subgroup A ‘pseudotypes’. The slopes of the neutralization curves for the heterologous systems differed from those of the homologous system. Neutralization indices derived from single points on the neutralization curves, because of the slope differences, did not show consistent cross-neutralization relationships of the viruses tested. When the slope differences were taken into account by comparing areas under the curves, the homologous system had an index at least 20% greater than the heterologous systems.
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