The differential immunogenicity of plant viral protein and nucleoproteins

Abstract

The empty protein shell (T) from turnip yellow mosaic virus (TYMV) preparations was less immunogenic in rabbits and mice than the infectious virus nucleoprotein (B 1), measured by levels of circulating precipitating antibodies. T was less immunogenic than B 1 in mice when introduced either intraperitoneally, intravenously or into the foot pad. The difference in antibody levels persisted throughout the time course of the primary response. A similar difference was found between T and B 1 in the secondary response in rabbits and mice. The precipitating antibodies elicited by T and B 1 in mice were identical as judged by double diffusion tests in agar. Isolated TYMV RNA did not augment the immunogenicity of T. Artificial empty protein shells produced from intact B 1 were no more immunogenic than natural T. TYMV nucleoprotein particles containing the full complement of viral RNA, but which were not infectious for Chinese cabbage, were as immunogenic as infectious B 1. In the primary response B 1 was eliminated from the blood stream of mice more rapidly than T, following intraperitoneal injection. Intact tobacco mosaic virus (TMV) and reconstituted TMV were more immunogenic in mice than TMV protein subunits or protein rods without RNA, considering only antibodies reacting with the intact virus. Although the role of the viral RNA in enhancing the immunogenicity of TYMV protein is not yet understood, it may have its effect at some early stage in the immune response.