[Immunochemical and electron microscopic analysis of the high-molecular structures in the tick-borne encephalitis...

High-molecular structures of tick-borne encephalitis virus were sedimented by centrifugation from virus-containing culture fluid and separated by sucrose concentration gradient centrifugation into 3 main fractions: rapidly sedimenting virions, the fraction sedimenting at a moderate rate, represented by "stellate" structures, and the fraction found on the top of the gradient and represented by structures similar in size and shape to virions, designated slowly sedimenting virions. The latter are first described in the paper. In immunodiffusion, the rapidly sedimenting virions form 1 of the 2 precipitation bands closer to the antigen-containing well, and in immunoelectrophoresis give 2 precipitation bands, anodic and cathodic, which fuse, indicating immunological identify of the 2 subpopulations of rapidly sedimenting virions. The slowly sedimenting virions in immunodiffusion form one of the 2 precipitation bands closer to the antigen well, and in immunoelectrophoresis form the cathodic precipitation band. The material sedimenting in the gradient at a moderate rate gives in immunodiffusion one precipitation band, the 3rd from the antigen well, and in immunoelectrophoresis forms a separate anodic precipitation band. This high-molecular non-virion antigen is found in small amounts also in fractions containing the rapidly sedimenting and slowly sedimenting virions. It is at least partially antigenically identical to previously studied low molecular non-virion ("soluble") antigen of tick-borne encephalitis virus.