Abstract
The live plague vaccine strain Y. pestis EV line NIIEG widely used for human and animal immunisation proves a high level of specific immunity against both bubonic and pneumonic plague. We constructed an EV NIIEG mutant in the acyltransferase gene lpxM that resulted in the production of a less toxic penta-acylated lipid A of lipopolysaccharide (LPS) of Y. pestis, tested the synthesis and immunoreactivity of the major known antigens involved in virulence and eliciting immunity against plague, and also evaluated the protective properties of the lpxM derivative.The expression of antigens was determined by dot-ELISA, immunoblotting, the indirect hemagglutination test, electron microscopy (capsule), and fibrinolytic and plasma-coagulase activities (plasminogen activator Pla). Stumulation of TNF-alpha production with different types of LPS was revealed by using the J774 macrophage-like cell line. The antibody immune response, followed by immunisation, was estimated by ELISA. Protective efficacy was evaluated in mice and guinea pigs by subcutaneous challenge with the wild-type Y. pestis 231.In comparison with the parental strain, the lpxM mutant was found to produce a reduced amount of capsular antigen F1, multifunctional virulence factor LcrV and murine toxin Ymt as well as had an altered activity of Pla. Moreover, this mutant possessed a modified cell surface as jusjed by the immunoreactivity with monoclonal antibodies to different carbohydrate epitopes and by the resistant phenotype to the plague diagnostic bacteriophage L-413C. The penta-acylated LPS of Y. pestis revealed a reduced capacity of stimulating TNF-alpha in vitro. Immunisation with the lpxM mutant provided an enhanced protection over the original Y. pestis EV NIIEG in both mice and guinea pigs. Thus, the pleiotropic effect of the lpxM mutation led to the construction of the live plague candidate vaccine strain with improved characteristics toward safety, reactogenicity and protective properties.
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