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pH6 Antigen in Plague Vaccine


Investigation of pH6 Antigen Role in Live Plaque Vaccine Immune-Genesis

Tech Area / Field

  • BIO-CGM/Cytology, Genetics and Molecular Biology/Biotechnology
  • BIO-MIB/Microbiology/Biotechnology
  • MED-VAC/Vaccines/Medicine
  • BIO-CHM/Biochemistry/Biotechnology

3 Approved without Funding

Registration date

Leading Institute
State Research Center for Applied Microbiology, Russia, Moscow reg., Obolensk


  • State University of New York at Stony Brook / Center for Infectious Diseases, USA, NY, Stony Brook

Project summary

Yersinia pestis, a causative agent of plague, is one of the most virulent microorganisms. At the same time, Yersinia pestis is considered to be a convenient model to study the fundamental problems of pathogenicity. The virulence of plague microbe is determined by a wide spectrum of characteristic features referred to as "determinants of virulence" (Burrows T., 1962; Brubaker,1972,1984). The ability of bacterial cells to absorb exogenous dyes and hemin (Pgm trait), to grow at 37 oC depending on the presence of Ca+2 ions in the medium (Cad trait), to synthesize VW antigens, "murine" toxin and capsule antigen F1 (Tox and Fra) as well as to perform concomitant synthesis of pesticine, fibrinolysin and plasmocoagulase (Pst, Fb, and Cg), or the ability to produce endogenous purines (Pur+) (Veinblat, 1974; Kutyrev et al., 1989), the socalled purine independence, belong to “classic” determinants. Recently, a number of additional virulence determinants has been identified. Outer membrane proteins (Yop's) (Brubaker,1984), adhesion pili (pH6 antigen) (Fosberg et al., 1997, 1998, 1999), adenylate cyclase, neuraminidase (Kutyrev et al.,1989), and sidero-binding proteins (Carniel et al., 1992) are among them.

F1 is the major immunogenic component of Y. pestis, whose synthesis is determined by pFra plasmid (60-65 Md) (Kutyrev et al.,1989). Expression of Y. pestis capsule F1 antigen is mediated by caf1M gene product, which has a homology with molecular chaperones of the other gram-negative bacteria (Holmgren et al.,1989; Bertin et al., 1993). "Chaperones" are a group of proteins united under a common name, whose function is to unfold proteins prior to translocation through the membrane and to catalyze the folding of proteins with the formation of tertiary structure (Rotman, Kornberg, 1986; Elis G., 1987). Capsule antigen is the major surface immunogen of Y. pestis. Of indubitable interest is to find out peculiarities of the interaction of proteins coded by fra-operon with immune response mediators, particularly with human interleukin-1 playing a key role in the development of immune process.

pH6 antigen was first described by Ben-Efraim in 1961 as an antigen synthesized by Y. pestis at a temperature close to body temperature of mammals and pH values close to pH of lysosomes in macrophages or abscesses. It was found that pH6 antigen expression is a necessary prerequisite of plague microbe virulence, although its role in the pathogenesis remains unclear (Linder et al., 1992). pH6 antigen was shown to be cytotoxic for macrophages (Bichowsky-Slonimsky, Ben-Efraim, 1963), suggesting its involvement into the macroorganism-microbe interactions. Linder et al (1990) studied in detail the molecular organization of pH antigen. It has been demonstrated that the protein is synthesized in a form of subunits with a molecular weight of 15 kDa, which readily aggregate into macromolecular complexes. The synthesis of pH6 antigen is coded by psa-operone having a chaperone-like structure similar to that of fra-operone for F1 antigen. Elimination of the gene coding for pH6 antigen from the chromosome of virulent plague microbial cells leads to a loss of virulence (Cherepanov et al., 1991; Panfertsev et al., 1991; Linder et al., 1993; Zav’alov V. et al., 1996). It has been demonstrated that pH6 antigen "covers" the plague microbe cells as FI capsule (Fosberg et al., 1997) and interacts with plasma lipoproteins membranes within macrophages (Makoveichuk E, et al., 2003).

Thus, in different periods of the existence within a macroorganism, plague microbe has two capsules determined by chaperone-like operons. It is also planned to clarify in what way and where one capsule is replaced for another one, and if this process correlates with (is dependent on, is involved into, contribute to) the infection of macrophage subpopulations and influences the next stages of plague vaccine immune-genesis. The main goal of this project is to elucidate the role of pH6 antigen at the initial stages of infectious process induced by the cells of live plague vaccines. All project tasks and methodical approaches for them solving were detail discussed with collaborators James Bliska from Department of Molecular Genetics and Microbiology, Center for Infectious Diseases (SUNY Stony Brook, USA) and Ake Forsberg from Department of Molecular Genetics and Microbiology, FOA (FOA, Umea, Sweden).