[Characteristics of the capsular antigen preparations isolated from a broth culture of Yersinia pestis strain EV].

The physico-chemical and immunobiological study of the preparation of capsular antigen, isolated by a high-yield method from the culture fluid of Y. pestis grown in nutrient broth at 37 degrees C and practically free from the admixture of polysaccharide and nucleic acids, has been made. The study has revealed that this capsular antigen is protein with a molecular weight of 1.65-1.69 X 10(6) D and sedimentation constant equal to 13.4S; its viscosity is 220 ml/g and its isoelectric point is at pH 4.1. The preparations have been found to possess immunogenic and allergenic properties and to be capable of sensitizing formulated, tannin-treated sheep red blood cells to plague antiserum.